Chemarkschemejun06-asa2

GCE Edexcel GCE Chemistry (8080/9080)

Summer 2006

Mark Scheme

Edexcel is one of the leading examining and awarding bodies in the UK and throughout the world. We provide a wide range of qualifications including academic, vocational, occupational and specific programmes for employers. Through a network of UK and overseas offices, Edexcel’s centres receive the support they need to help them deliver their education and training programmes to learners. For further information please call our Customer Services on 0870 240 9800, or visit our website at www.edexcel.org.uk.

Summer 2006 Publications Code UA017774 All the material in this publication is copyright © Edexcel Ltd 2006

Contents Unit 6241/01 .............................................................................................................................................1 Unit 6242/01 .............................................................................................................................................7 Unit 6243/01A Practical Test Group 1 ..................................................................................................15 Unit 6243/01B Practical Test Group 2 ..................................................................................................21 Unit 6243/01C Practical Test Group 3 ..................................................................................................29 Unit 6243/02 ...........................................................................................................................................35 Unit 6244/01 ...........................................................................................................................................41 Unit 6245/01 ...........................................................................................................................................51 Unit 6246/01A Practical Test Group 1 ..................................................................................................65 Unit 6246/01B Practical Test Group 2 ..................................................................................................73 Unit 6246/01C Practical Test Group 3 ..................................................................................................81 Unit 6246/02 ...........................................................................................................................................89

Using the mark scheme The mark scheme gives you: • an idea of the types of response expected • how individual marks are to be awarded • the total mark for each question • examples of responses that should NOT receive credit. Candidates must make their meaning clear to the examiner to gain the mark. Make sure that the answer makes sense. Do not give credit for correct words/phrases which are put together in a meaningless manner. Answers must be in the correct context. 1 / means that the responses are alternatives and either answer should receive full credit. 2 ( ) means that a phrase/word is not essential for the award of the mark, but helps the examiner to get the sense of the expected answer. 3 [ ] words inside square brackets are instructions or guidance for examiners. 4 Phrases/words in bold indicate that the meaning of the phrase or the actual word is essential to the answer. 5 ecf/TE/cq (error carried forward) means that a wrong answer given in an earlier part of a question is used correctly in answer to a later part of the same question.

8080/9080 Chemistry Summer 2006

ii

Unit 6241/01 1

..2s22p2 OR 1s22s22p2 OR (1s2)2s22px12py1 ALLOW capitals and subscripts

(1 mark)

(b)

large gap/jump between 4th and 5th ionisation energies (so fifth in inner shell)

(1 mark)

(c)

4 pairs of electrons around C atom (1) all Ione pairs shown (1) Mark independently

(a)

xx x x

x x x

xx

x

Cl x xo

x

xx

x

Cl o C o Cl x

xx

x x

xo

xx

x

Cl x

xx

ALLOW all dots/crosses Any attempt at an ionic diagram (0) (d)

(i)

(2 marks)

High energy/fast/gun electrons hit/strike OR bombarded by electrons (1) Removes/knocks out electron (1) OR equation eg X → X+ + e (−) IGNORE state symbols If knock out is mentioned, hit/strike is not required in 1st mark

(e)

(ii)

magnetic field/magnet/electromagnet/magnetic plates

(i)

mass of one atom (of the isotope) (1) relative to 1/12th of the mass of (1) a carbon -12 atom (1)

(2 marks) (1 mark)

OR 2nd and 3rd marks can be awarded as follows: On a scale where a 12C atom (1) has a mass of 12 (NOT grams) (1) Word “atom” need only be mentioned once Word “mass” need only be mentioned once If define R.A.M……max1

(3 marks)

(ii)

162 IGNORE units

(1 mark)

(iii)

(atoms with) same no. of protons (1) NOT same atomic number “different number of electrons” loses 1st mark but IGNORE “same number of electrons” different number of neutrons (1) NOT different mass number Penalise incorrect reference to number of electrons

(iv)

same number of electrons

IGNORE “same number of protons”

OR same electronic configuration/pattern/structure NOT same number in outer orbit

8080/9080 Chemistry Summer 2006

(2 marks)

1

(1 mark) Total 14 marks

2

(a)

(i)

Covalent

(1 mark)

(ii)

Induced-dipole(-induced dipole)/dispersion/London/v der Waals/vdw Temporary or instantaneous can be used instead of induced NOT “dipole” forces NOT permanent dipole NOT dipole-dipole

(iii)

(1 mark)

polymer has stronger/more vdw/intermolecular forces (1) ALLOW dipole forces because it has more electrons/larger electron cloud/more contact area (1) NOT larger molecules/surface area

(b)

so more energy/heat needed to overcome/break these forces OR so more energy/heat needed to separate these molecules (1) NOT breaking bonds 3rd mark is NOT stand alone strong attraction between Mg ions/Mg2+/cations/metal ions (1) NOT electrostatic forces/metallic bonds and delocalised/sea of electrons (1) Mark independently

(c)

(3 marks)

(2 marks)

Ionic/electrovalent (1) diagram shows alternating cations and anions in planar arrangement (1) 2nd mark

OR labelled “blobs” – minimum labelling is “Na/sodium ion” and “chloride ion” in 3-D structure/at least 2 (part) layers shown (1) 2nd and 3rd marks Na+

ClNa+

ClNa+

Cl-

ClNa+

(2)

OR ClCl-

Na+

ClNa

and

+

Cl-

ClCl-

Na+ Cl

Na+

-

Na+

Na+ +

Na

(2) If only one of them given (1)

(3 marks) Total 10 marks

8080/9080 Chemistry Summer 2006

2

3

(a)

(i)

Red/brick-red/orange-red (1) NOT ‘Orange’ on its own (2 marks)

Yellow (1) ALLOW orange (ii)

electrons promoted (by heat/flame to a higher level) (1) NOT electrons excited fall back down/return (1) (3 marks)

emit light (1) (b)

(i)

(ii)

(c)

(d)

2Na + 2H2O → 2NaOH + H2 OR ½ this OR multiples of this IGNORE state symbols

(1 mark) (1 mark)

Na2O + H2O → 2NaOH OR ½ this OR multiples of this IGNORE state symbols

Bubbles/fizz/effervescence (1) float/move about (on surface) (1) melts/forms sphere (1) gets smaller/disappears (1) burns with yellow flame (1) IGNORE dissolves OR gets hot IGNORE explodes/ignites

IGNORE gas/fumes Any two

(2 marks)

KO2 OR O2K

(1 mark) Total 10 marks

8080/9080 Chemistry Summer 2006

3

4

(a)

(i)

-1/-I, 0 -1/-I, 0 minus can be either side, sub or superscript iodine no’s correct chlorine no’s correct

(ii)

(1) (1)

(2 marks)

chlorine oxidation number goes down/goes from 0 to -1, so reduced (1) iodine oxidation number goes up/goes from -1 to 0, so oxidised (1) Mark consequentially on (a)(i)

(iii)

(2 marks)

moles NaI= 30.0 = 0.2 (1) 150 moles I2 = 0.1 (1) mass of I2 = 0.1 x 254 = 25.4 (g) (1) OR 300g NaI (1) => 254g I2 (1) 30.0 x

254 = 25.4(g) (1) 300

Correct answer with some working (3) Use of atomic numbers 2 max Penalise wrong units (iv) (b)

(i)

vol = 0.1 x 24 = 2.4 (dm3) If not 2.4, check for consequential on (a)(iii)

(2 marks)

I(g) → I+(g) + e(−)

OR

I(g) – e(−) → I+(g)

species (1) state symbols (1) – award state symbols mark only if species correct and in correct place, or if wrong halogen used If I2 OR ½I2 (0) (iii)

(1 mark)

black/grey/grey-black (1) NOT blue-black NOT purple IGNORE shiny/silvery Solid (1)

(ii)

(3 marks)

(2 marks)

nuclear charge increases/more protons (1) (but) more shielding/screening OR extra shells between outer shell/valence/electrons and nucleus (1) outer electron further from nucleus/iodine’s outer electron in higher energy level/shell (therefore less energy). (1) ACCEPT “electron being removed” instead of “outer” (3 marks) Total 15 marks

8080/9080 Chemistry Summer 2006

4

5

(a)

(i)

4 pairs of electrons /2 Ione pairs and 2 bond pairs (1) so electron pairs arranged tetrahedrally OR Arranged to give maximum separation/minimum repulsion (1)

(ii)

103 – 105

(°)

(2 marks)

(1) (2 marks)

lone pair repulsion> bond pair repulsion (1) (b)

(i)

trigonal planar diagram (1) e.g two opposite wedges gets (1) three wedges of two types gets (1) one wedge only gets (0) IGNORE name 120

(ii)

(iii)

(iv)

(°)

B and Cl have different electronegativities / Cl more electronegative than B OR different electronegativities explained Dipoles (or vectors) cancel/symmetrical molecule/centres of positive and negative charges coincide IGNORE polarity cancels

(1 mark)

(1 mark)

Induced-dipole(-induced dipole)/dispersion/London/v der Waals/vdw Temporary or instantaneous can be used instead of induced NOT “dipole” forces NOT permanent dipole NOT dipole-dipole

(c)

(2 marks)

marked on diagram (1) – stand alone

(1 mark)

14.9 = (0.481) 31

85.1 = (2.40) 35.5

0.481 = 1 0.481

2.40 = 5 , so PCl5 (1) 0.481

(1)

(2 marks)

Use of atomic number max 1

Total 11 marks Paper Total: 60 Marks

8080/9080 Chemistry Summer 2006

5

8080/9080 Chemistry Summer 2006

6

Unit 6242/01 1.

(a)

(b)

(i)

(aqueous) sodium hydroxide ALLOW formula

(1 mark)

(ii)

Cryolite/Sodium aluminofluoride/Na3AlF6

(1 mark)

(iii)

Melting temperature/point is too/very high NOT “too much energy is required”

(1 mark)

Al3+ + 3e(−) Æ Al IGNORE state symbols

(1 mark)

(i) (ii)

liberated oxygen OR 2O2− Æ O2 + 4e(−) (1) If say O2 is liberated but equation wrong, give the mark, ignoring the equation Oxidises/reacts with carbon anodes OR burns away (1) The carbon can come from an equation Either C + O2 Æ CO2 OR C + 2O2− Æ CO2 + 4e(−) OR C+ O2− Æ CO + 2e(−) OR 2C+ O2 Æ 2CO

(c)

Use Cans (1) Aeroplanes (1) Saucepans (1) Cooking foil (1) Car bodies/engines (1) Power cables (1) NOT electrical wiring - though this can score the second mark Window/greenhouse frames (1)

Bicycle frames/parts (1)

(1)

(3 marks)

Property Does not corrode OR non-toxic (1) Low density OR high strength:weight ratio (1) NOT ‘light’ Good conductor of heat OR non-toxic (1) Good conductor of heat OR non-toxic (1) Does not corrode OR Does not oxidise OR low density (1) High conductivity OR low density (1) Does not corrode OR easily extruded (1) NOT ‘do not rust’ as synonym for ‘corrode’ Low density (1) (2 marks) Total 9 marks

8080/9080 Chemistry Summer 2006

7

2

(a) Primary

Isomer CH3CH2CH2CH2OH (1) OR C2H5CH2CH2OH OR (CH3)2CHCH2OH (1)

Complete oxidation CH3CH2CH2COOH (1) (CH3)2CHCOOH (1)

O

NOT C3H7CH2OH etc

CH3CH2CH2 C

NOT OHCH2CH2CH2CH3

OH

(1) ALLOW C2H5CH2COOH OR

O (CH3)2CHC

OH

ALLOW (CH3)2CH COOH -CO2H allowable for COOH C2H5 allowable for CH3CH2Secondary

CH3CH2CH(OH)CH3 (1)

O CH3CH2CCH3

Tertiary

(1) ALLOW CH3CH2COCH3 None (1) ALLOW “No structure”

(CH3)3COH (1)

MUST be stated eg n/a OR no product OR repeat the test alcohol formula ie (CH3)3COH NOT just a line Stand alone mark Incorrect alcohol repeated 0 (out of 2) The oxidation products are stand alone marks If three carbon alcohols shown, correct oxidation products only score (6 marks)

8080/9080 Chemistry Summer 2006

8

(b)

(i)

1(-)iodopropane

(1 mark)

(ii)

Moist/wet/damp/aqueous/aq IGNORE any reference to heat

(1 mark)

(iii) (c)

(i)

PI3 ALLOW PI5 NOT names Ethanol/propanone/aqueous ethanol/alcohol (1) heat (1) OR warm (under reflux) OR boil under reflux ALLOW ‘reflux’ If a temperature is stated must be between 30 ° and 80 ° C

(ii)

(iii)

(1 mark)

(2 marks)

CH3CH2CH2CN ALLOW C2H5CH2CN NOT C3H7CN Cyanide group can be –C≡ N but not –N≡ C – if bond shown it must be correct

(1 mark)

nucleophilic substitution

(1 mark) Total 13 marks

8080/9080 Chemistry Summer 2006

9

3

(a)

Fine powder because it has larger surface area (1) so more collisions per unit time OR greater collision frequency (between the peroxide and the catalyst) (1) OR ‘more active sites’ OR ‘more likely for collisions to occur’ NOT ‘more successful collisions’. NOT ‘more collisions’ on its own

(b)

(i)

(2 marks)

Axes labels (1) ie y-axis = Number/“N” /fraction of molecules x-axis = (kinetic) energy/E NOT potential energy Start at or going towards origin, asymmetric, asymptotic to x-axis, T1 line correct shape (1) T2 line peak lower (1) and to the right (1) T2 line must only cross T1, line once, otherwise max (1)

(4 marks)

(ii)

Ea shown well to the right of both peaks (1) larger area for T2 shown on diagram and related to number of collisions/molecules with E ≥ Ea (1) – need to refer to shading Greater proportion of successful collisions OR more of the collisions are successful (1) ACCEPT more successful collisions per unit time NOT ‘more successful collisions’ alone

(3 marks)

(iii) Ea (cat) at a lower energy than Ea (1) – check diagram, it is enough to draw it on the diagram Greater proportion of molecules have energy greater than the new activation energy OR relates areas to frequency of successful collisions (1)

(2 marks)

Total 11 marks

8080/9080 Chemistry Summer 2006

10

4

(a)

Heat/enthalpy/energy change per mole of substance/compound/product OR heat/enthalpy/energy change for the formation of 1 mol of substance/ compound/product (1) “heat released” and “heat required” not allowed unless both mentioned NOT molecule from its elements in their standard states (1) at 1 atm pressure and a stated temperature/298 K (1) NOT “room temperature and pressure” NOT “under standard conditions”

(b)

(i)

(∆H = - 306 – (- 399)) = (+) 93 (kJ mol – 1 ) ALLOW kJ Incorrect units lose mark otherwise

(ii)

(3 marks)

(1 mark)

The equilibrium moves to right hand side OR amount of dissociation increases (1) Because the (forward) reaction is endothermic (1) Needs to be consistent with (i) If (i) has a negative answer (exothermic) equilibrium moves to left hand side (1) Because (forward) reaction is exothermic (1) If answer to (i) is +93 or 93 but state that this is exothermic If reaction moves to left hand side (1) If reaction moves to right hand side (0)

(iii)

(2 marks)

add chlorine (1) which drives equilibrium to the left (1) OR increase the (total) pressure (1) because there are fewer (gas) molecules on left hand side (1) OR add PCl3 (1) Which drives equilibrium to the left (1)

(2 marks) Total 8 marks

8080/9080 Chemistry Summer 2006

11

5

(a)

(i)

(ii)

(b)

÷Ar to give 1.06, 2.13 and 1.06 (1) DO NOT ALLOW 1, 2, 1 for this mark (divide by smallest to) to give CH2Br (1) CH2Br on its own 1 (out of 2)

(2 marks)

CH2Br mass = 94 (1) (which is half 188) so MF is C2H4Br2 (1) C2H4Br2 on its own 1 (out of 2)

(2 marks)

(iii)

HOCH2CH2OH / CH2OHCH2OH ALLOW (CH2OH)2

(iv)

BrCH2CH2Br / CH2BrCH2Br ALLOW CH3CHBr2 only if in (iii) they have CH3CH(OH)2. No other consequential marking allowed

(1 mark)

(1 mark)

Strength of bonds C-I < C-Br < C-Cl (1) Must be bonds to carbon. C-I bond is weakest because C- I bond longest OR I largest atom (1) NOT ion so Ea for the reaction with the iodide is lower (1) NOT kinetically more stable The marks can be awarded for the inverse argument based on the C-Cl bond being the strongest because Cl is the smaller atom. The 3rd mark is stand alone If electronegativity differences are used then they must be used correctly; so if electronegativity difference is said to increase rates in the same way as bond strength then 2 max

(3 marks) Total 9 marks

8080/9080 Chemistry Summer 2006

12

6

(a)

(i)

(ii)

Concentrated/saturated sodium chloride OR concentrated/saturated brine NOT sodium chloride on its own NOT aqueous sodium chloride alone on its own

(1 mark)

anode 2Cl− Æ Cl2 + 2e(−) (1) OR halved ALLOW -2e(−) on LHS Cathode 2H2O + 2e(−) ÆH2 + 2OH− OR 2H+ + 2e(−) Æ H2 (1) OR halved IGNORE state symbols NOT Cl for ½ Cl2 NOT H for ½ H2. If these equations are interchanged then (1) if they are otherwise correct.

(iii)

Water sterilisation/treatment NOT purification Manufacture of anaesthetics Bleaching Bleach manufacture Specified solvent manufacture Papermaking Manufacture of HCI/hydrochloric acid Extraction of bromine from sea water Manufacture of titanium Manufacture of herbicides or insecticides.

Any one

NOT swimming pools on its own NOT PVC manufacture (iv)

(2 marks)

(1 mark)

Permits passage of sodium ions/cations (1) Does not allow Cl−/anions through (1) OR selectively permeable (1) NOT semi-permeable allows Na+ /does not allow Cl− to pass (1) NOT ‘prevents hydrogen and chlorine from reacting’ NOT ‘prevents chlorine and sodium hydroxide from reacting’

8080/9080 Chemistry Summer 2006

13

(2 marks)

(b)

Skeleton (1) - This must show a 2-carbon repeat unit although number of C’s does not matter Continuation bonds (1) - This is allowable if hydrogens are missed, or if a long chain is shown. IGNORE any n

H H C C

ACCEPT

CH2CHCl

H Cl brackets not needed here

(2)

ACCEPT

H H H H C C C C H Cl H Cl repeat unit

(c)

(d)

(2 marks)

If C=C bond shown then (0) resistant to chemical attack OR not biodegradable NOT “does not decompose” NOT rigidity

(1 mark)

produces toxic/poisonous/acidic fumes ALLOW HCI instead of “fumes” NOT chlorine If a list is given and one item is wrong then (0)

(1 mark) Total 10 marks Total for paper: 60 marks

8080/9080 Chemistry Summer 2006

14

Unit 6243/01A Practical Test Group 1 Penalise SF once on the whole paper. Write “SF” to show where the penalty has been applied. Indicate “SF” on the front cover grid next to the question. 1.

(a)

(i)

Observation Milky/cloudy/white ppt (1) Inferences Carbon dioxide/CO2 (1) “carbonate or hydrogencarbonate” both needed (1) ACCEPT correct formulae If both formula and name given, both must be correct

(ii)

(3 marks)

Add solid to hot water (1) hydrogencarbonate gives gas, carbonate no reaction (1) OR heat solution with phenolphthalein (1) carbonate pink in cold, hydrogencarbonate colourless in cold/goes pink on heating (1) OR Add calcium/magnesium/barium ion solution or Ca2+/Mg2+/Ba2+ solution or soluble compounds of calcium/magnesium/barium (1) White ppt with carbonate, no ppt with hydrogencarbonate (1) OR Measure/find/determine pH of solution (1) pH < 10 hydrogencarbonate, pH > 10 carbonate (1) If only one ion in inference, no marks for (ii) If no final inference given, can still get 2 marks for (ii)

(b)

Lilac/mauve (flame) (1) ALLOW purple potassium ion (1) ALLOW K+/ K / potassium

(c)

(2 marks)

(2 marks)

litmus turns blue (1) ammonia/NH3 (1) nitrate/NO3− OR nitrite/NO2− (1) - Any mention of ammonium negates 3rd mark If name and formula given, both must be correct

(3 marks) (Total 10 marks)

8080/9080 Chemistry Summer 2006

15

2.

(a)

Table 1

Check subtractions and averaging arithmetic, correcting if necessary. All volumes recorded to 0.05 cm3 (1) ALLOW one slip but withhold this mark if any readings are in the wrong boxes. ALLOW 0, 0.0, 0.00 as initial volume NOT 50 as initial volume All subtractions correct (1) [99top RHS of Table 1]

Mean titre

For correct averaging of chosen values/choosing identical values and for recording the average correct to 2 or 3 dps or to nearest 0.05 cm3 (1) - unless already penalised [9 by the mean in space or near the dotted line in paragraph below]

Accuracy

If the candidate has made an arithmetical error in the Table 1 volumes used in the mean or in averaging the examiner must calculate a new average. • For an averaging error simply calculate a new value using the candidate’s chosen titres. • If a wrongly subtracted titre has been used in the mean then choose any two identical titres or take an average of the closest two titres. Calculate the difference between the candidate’s mean titre and that of the examiner or supervisor. Record the difference on the scripts as d = Examiner’s titre = 22.60 cm3 [or comparison with Supervisor’s value (International only). Examiner to write “SR = titre value” on each script] Award marks for accuracy as follows.

Difference d = Mark

8080/9080 Chemistry Summer 2006

±0.20

±0.30

±0.40

±0.60

±0.80

±1.00

>1.00

6

5

4

3

2

1

0

16

Range

Award a mark on the range of titres used by the candidate to calculate the mean. The range(r) is the difference between the outermost titres used to calculate the mean. If the examiner has corrected titres because of incorrect subtraction then award the range mark on the corrected titres used by the examiner to re-calculate the mean.

Range(r) of titres used in mean / cm3 Mark

±0.20

±0.30

±0.50

>0.50

3

2

1

0

Examiner to show the marks awarded for accuracy and range as d= value

9

r = value

6 max

9 3 max

Then the mark out of 12 written in margin.

(b)

(i)

(ii) (iii)

(12 marks)

25 x 0.0450 OR 1.125 x10-3 (mol) 1000 Mark is for the process IGNORE SF IGNORE units

(1 mark)

answer to (i) x 2 Mark is for the process

(1 mark)

answer to (ii) x 1000 mol dm-3 titre Mark is for the numerical answer to 3 or 4 SF

(1 mark) (Total 15 marks)

8080/9080 Chemistry Summer 2006

17

3.

(a)

Table 2 All data to 1 dp ONLY (1) correct temperature change for data recorded (1) Temperatures Accuracy mark based on corrected (if necessary) subtraction Exp 1: 3.0 − 4.0

o

(2); 2.0 − 5.0

o

(1); outside limits (0)

Exp 2: 7.0 − 8.0

o

(2); 6.0 − 9.0

o

(1); outside limits (0)

Exp 3: 9.5 − 10.5 o (2); 8.5 − 11.5 o (1); outside limits (0)

(8 marks)

International Centres ONLY: Temperatures - Accuracy mark based on corrected (if necessary) subtraction ± 0.5 of Supervisor (2) ± 1.5 of Supervisor (1) Outside limits (0) for each temperature (b)

∆T must be plotted (i)

y-scale linear from zero to cover at least half the vertical distance (1) All plotting points (even on a linear scale which does not start at zero) ± ½ a square on the y axis but volume spot on (1) Best line through origin (1)

(ii)

∆y and ∆x marked OR triangle drawn with ∆V of at least 10 cm3 (1)

(3 marks)

Correct values irrespective of size of triangle (1) Calculation ∆y (1) – mark is for the process, can be left as a ∆x fraction

(iii)

8080/9080 Chemistry Summer 2006

Check the graph, if all three ticks awarded on graph carry mark over to margin in (ii).

(3 marks)

Substitution into equation to find enthalpy change Mark is for final answer which must have a negative sign and be no more than 3 SF (unless SF already penalised) IGNORE units

(1 mark)

18

25.0 cm3 (of R) (1)

(iv)

because the total volume for each experiment has to be 60 cm3/the same/constant (1) – stand alone If Vtotal is miscalculated, but recognition of same/constant total volume allow 2nd mark

(2 marks) (Total 17 marks)

4.

Read through all of the plan first P

9

T

9

Mix two (or more) pairs (1) Record/measure temperature change (1) If no change (1) pair of acids (1) Correct identification of alkali

9 i4

If candidate pre-supposes which is which zero (out of 4) here, but marks for second part are still available.

E

9

R

9

∆

9

Mix equal volumes of each acid and alkali (1) Repeat/done with each acid (1) – stand alone Record/measure ∆T (1) – dependent on E9 being awarded Bigger change is for sulphuric acid (1) – dependent on E9 mark being awarded The second four marks are independent of the first four. 9 4w

If the second part is correctly done

(8 marks) END of GROUP 1

8080/9080 Chemistry Summer 2006

19

Materials Each candidate will require: (a)* 1 g of a mixture of potassium hydrogencarbonate and potassium nitrate (approximately 50% of each by mass), labelled M. The identity of this must not be disclosed to candidates; (b)* 125 cm3 of aqueous ethanedioic acid concentration 0.0450 mol dm–3 labelled Ethanedioic acid solution S; (c)* 125 cm3 of aqueous sodium hydroxide concentration 0.10 mol dm–3 labelled Solution P. The concentration of this must not be disclosed to candidates; (d)* 100 cm3 of aqueous sodium hydroxide concentration 1.0 mol dm–3 labelled Solution Q; (e)* 120 cm3 of aqueous sulphuric acid concentration 1.0 mol dm–3 labelled Solution R; (f) 10 cm3 of limewater; (g) 2 cm3 of aqueous hydrochloric acid; concentration approximately 1 mol dm–3; (h) 2 cm3 of aqueous sodium hydroxide; concentration approximately 1 mol dm–3; (i) aluminium foil, approximately 1 cm square; (j) red litmus paper; (k) phenolphthalein indicator; (l) distilled water.

8080/9080 Chemistry Summer 2006

20

Unit 6243/01B Practical Test Group 2 Penalise SF once on the whole paper. Write “SF” to show where the penalty has been applied. Indicate “SF” on the front cover grid next to the question. 1.

(a)

yellow (flame) (1) ALLOW Orange sodium ion (1) ALLOW Na+ / Na / sodium

(b)

(i)

(ii)

(2 marks)

white ppt (1) NOT misty/cloudy chloride/Cl− (1) ALLOW AgCl/silver chloride NOT chlorine ALLOW inference from misty/cloudy

(2 marks)

Add dilute/aq ammonia (1) ppt dissolves (1) OR Leave in UV/ daylight (1) Goes purple/black (1) OR Add conc. sulphuric acid to (solid) N (1) Steamy/misty/white fumes (1) NOT white smoke If chlorine given in (i) allow sensible description of ppt dissolving in dilute/aqueous ammonia.

(c)

Melts / bubbles/decomposes (1) re-lights splint / splint glows more brightly (1) IGNORE “pop” oxygen / O2 (1) nitrate / NO3− (1) NOT nitrite ALLOW chlorate NOT bromate

(2 marks)

(4 marks) (Total 10 marks)

8080/9080 Chemistry Summer 2006

21

2.

(a)

Table 1

Check subtractions and averaging arithmetic, correcting if necessary. All volumes recorded to 0.05 cm3 (1) ALLOW one slip but withhold this mark if any readings are in the wrong boxes. ALLOW 0, 0.0, 0.00 as initial volume NOT 50 as initial volume All subtractions correct (1) [99top RHS of Table 1]

Mean titre

For correct averaging of chosen values/choosing identical values and for recording the average correct to 2 or 3 dps or to nearest 0.05 cm3 (1) - unless already penalised [9 by the mean in space or near the dotted line in paragraph below]

Accuracy

If the candidate has made an arithmetical error in the Table 1 volumes used in the mean or in averaging the examiner must calculate a new average. • For an averaging error simply calculate a new value using the candidate’s chosen titres. • If a wrongly subtracted titre has been used in the mean then choose any two identical titres or take an average of the closest two titres. Calculate the difference between the candidate’s mean titre and that of the examiner or supervisor. Record the difference on the scripts as d = Examiner’s titre = 24.65 cm3 [or comparison with Supervisor’s value (International only). Examiner to write “SR = titre value” on each script] Award marks for accuracy as follows.

Difference d = Mark

8080/9080 Chemistry Summer 2006

±0.20

±0.30

±0.40

±0.60

±0.80

±1.00

>1.00

6

5

4

3

2

1

0

22

Range

Award a mark on the range of titres used by the candidate to calculate the mean. The range(r) is the difference between the outermost titres used to calculate the mean. If the examiner has corrected titres because of incorrect subtraction then award the range mark on the corrected titres used by the examiner to re-calculate the mean.

Range(r) of titres used in mean / cm3 Mark

±0.20

±0.30

±0.50

>0.50

3

2

1

0

Examiner to show the marks awarded for accuracy and range as d= value

9

(b)

r = value

6 max

9 3 max

Then the mark out of 12 written in margin.

(12 marks)

25 x 0.0480 OR 1.20 ×10-3 (mol) 1000 Mark is for the process IGNORE SF IGNORE units

(1 mark)

(ii)

answer to (i) x 2 Mark is for the process

(1 mark)

(iii)

answer to (ii) x 1000 mol dm-3 titre

(i)

Mark is for the numerical answer to 3 or 4 SF

(1 mark) (Total 15 marks)

8080/9080 Chemistry Summer 2006

23

3.

(a)

Table 2 All data to 1 dp ONLY (1) correct temperature change for data recorded (1) Temperatures Accuracy mark based on corrected (if necessary) subtraction Exp 1: 3.0 − 4.0

o

(2); 2.0 − 5.0

o

(1); outside limits (0)

Exp 2: 6.0 − 7.0

o

(2); 5.0 − 8.0

o

(1); outside limits (0)

Exp 3: 8.5 − 9.5 o (2); 7.5 − 10.5 o (1); outside limits (0)

(8 marks)

International Centres ONLY: Temperatures - Accuracy mark based on corrected (if necessary) subtraction ± 0.5 of Supervisor (2) ± 1.5 of Supervisor (1) Outside limits (0) for each temperature (b)

∆T must be plotted (i)

y-scale linear from zero to cover at least half the vertical distance (1) All plotting points (even on a linear scale which does not start at zero) ± ½ a square on the y axis but volume spot on (1) Best line through origin (1)

(ii)

∆y and ∆x marked OR triangle drawn with ∆V of at least 10 cm3 (1)

(3 marks)

Correct values irrespective of size of triangle (1) Calculation ∆y (1) – mark is for the process, can be left as a ∆x fraction

(iii)

8080/9080 Chemistry Summer 2006

Check the graph, if all three ticks awarded on graph carry mark over to margin in (ii).

(3 marks)

Substitution into equation to find enthalpy change Mark is for final answer which must have a negative sign and be no more than 3 SF (unless SF already penalised) IGNORE units

(1 mark)

24

(iv)

42.5 cm3 (of W) (1) because the total volume for each experiment has to be 60 cm3/ the same/constant (1) – stand alone If Vtotal is miscalculated, but recognition of same/constant total volume allow 2nd mark

(2 marks)

(Total 17 marks)

8080/9080 Chemistry Summer 2006

25

4.

Read through all of the plan first P

9

T

9

Mix two (or more) pairs (1) Record/measure temperature change (1) If no change (1) pair of acids (1) Correct identification of alkali

9 i4

If candidate pre-supposes which is which zero (out of 4) here, but marks for second part are still available.

E

9

R

9

∆

9

Mix equal volumes of each acid and alkali (1) Repeat/done with each acid (1) – stand alone Record/measure ∆T (1) – dependent on E9 being awarded Bigger change is for 2 M HCl (1) – dependent on E9 being awarded The second four marks are independent of the first four. 9 4w

If the second part is correctly done

(8 marks) END of GROUP 2

8080/9080 Chemistry Summer 2006

26

Materials Each candidate will require: (a)* 1 g of a mixture of sodium chloride and sodium nitrate (approximately 50% of each by mass), labelled N. The identity of this must not be disclosed to candidates; (b)* 125 cm3 of aqueous ethanedioic acid concentration 0.0480 mol dm–3 labelled Ethanedioic acid solution T; (c)* 125 cm3 of aqueous sodium hydroxide concentration 0.10 mol dm–3 labelled Solution U. The concentration of this must not be disclosed to candidates; (d)* 100 cm3 of aqueous sodium hydroxide concentration 1.0 mol dm–3 labelled Solution V; (e)* 120 cm3 of aqueous sulphuric acid concentration 1.0 mol dm–3 labelled Solution W; (f) 2 cm3 aqueous nitric acid; concentration approximately 0.5 mol dm–3; (g) 2 cm3 of aqueous silver nitrate; concentration approximately 0.05 mol dm–3; (h) phenolphthalein indicator; (i) distilled water.

8080/9080 Chemistry Summer 2006

27

8080/9080 Chemistry Summer 2006

28

Unit 6243/01C Practical Test Group 3 Penalise SF once on the whole paper. Write “SF” to show where the penalty has been applied. Indicate “SF” on the front cover grid next to the question. 1.

(a)

(i)

(Red litmus) turns blue (1) white ppt (1) ammonia/NH3 (1) Ammonium ion (1) (5 marks)

“Group 2 (cation)” OR list of at least two group 2 cations (1) (ii)

white ppt (1) not misty/cloudy but allow inference sulphate/SO42− (1) allow BaSO4/Barium sulphate IGNORE HSO4−

(iii)

(2 marks)

white ppt (1) magnesium / Mg2+ confirmed (1) Calcium (0) “Calcium/magnesium” (0)

(b)

(2 marks)

(NH4)2SO4 OR MgSO4 If both are given BOTH must be correct; no consequential marking;formula must follow inferences; allow MgSO4 from two ions in (iii)

(1 mark)

(Total 10 marks)

8080/9080 Chemistry Summer 2006

29

2.

(a)

Table 1

Check subtractions and averaging arithmetic, correcting if necessary. All volumes recorded to 0.05 cm3 (1) ALLOW one slip but withhold this mark if any readings are in the wrong boxes. ALLOW 0, 0.0, 0.00 as initial volume NOT 50 as initial volume All subtractions correct (1) [99top RHS of Table 1]

Mean titre

For correct averaging of chosen values/choosing identical values and for recording the average correct to 2 or 3 dps or to nearest 0.05 cm3 (1) - unless already penalised [9 by the mean in space or near the dotted line in paragraph below]

Accuracy

If the candidate has made an arithmetical error in the Table 1 volumes used in the mean or in averaging the examiner must calculate a new average. • For an averaging error simply calculate a new value using the candidate’s chosen titres. • If a wrongly subtracted titre has been used in the mean then choose any two identical titres or take an average of the closest two titres. Calculate the difference between the candidate’s mean titre and that of the supervisor. Record the difference on the scripts as d = Comparison with Supervisor’s titre [Examiner to write “SR = titre value” on each script] Award marks for accuracy as follows.

Difference d = Mark

8080/9080 Chemistry Summer 2006

±0.20

±0.30

±0.40

±0.60

±0.80

±1.00

>1.00

6

5

4

3

2

1

0

30

Range

Award a mark on the range of titres used by the candidate to calculate the mean. The range(r) is the difference between the outermost titres used to calculate the mean. If the examiner has corrected titres because of incorrect subtraction then award the range mark on the corrected titres used by the examiner to re-calculate the mean.

Range(r) of titres used in mean / cm3 Mark

±0.20

±0.30

±0.50

>0.50

3

2

1

0

Examiner to show the marks awarded for accuracy and range as d= value

9

r = value

6 max

9 3 max (12 marks)

Then the mark out of 12 written in margin.

(b)

(i)

(ii) (iii)

25 x 0.0480 [or conc from centre] 1000 Mark is for the process IGNORE SF IGNORE units

OR 1.20 ×10-3 (mol)

answer to (i) x 2 Mark is for the process

(1 mark) (1 mark)

answer to (ii) x 1000 mol dm-3 titre Mark is for the numerical answer to 3 or 4 SF

(1 mark) (Total 15 marks)

8080/9080 Chemistry Summer 2006

31

3.

(a)

Table 2 All data to 1 dp ONLY (1) correct temperature change for data recorded (1) International Centres ONLY: Temperatures - Accuracy mark based on corrected (if necessary) subtraction ± 0.5 of Supervisor (2) ± 1.5 of Supervisor (1) Outside limits (0) for each temperature

(b)

(8 marks)

∆T must be plotted (i)

y-scale linear from zero to cover at least half the vertical distance (1) All plotting points (even on a linear scale which does not start at zero) ± ½ a square on the y axis but volume spot on (1) Best line through origin (1)

(ii)

(3 marks)

3

∆y and ∆x marked OR triangle drawn with ∆V of at least 10 cm (1) Correct values irrespective of size of triangle (1) Calculation ∆y (1) – mark is for the process, can be left as a ∆x fraction

(iii)

(iv)

Check the graph, if all three ticks awarded on graph carry mark over to margin in (ii).

(3 marks)

Substitution into equation to find enthalpy change Mark is for final answer which must have a negative sign and be no more than 3 SF (unless SF already penalised) IGNORE units

(1 mark)

37.0 cm3 (of W) (1) because the total volume for each experiment has to be 60 cm3/ the same/constant (1) – stand alone If Vtotal is miscalculated, but recognition of same/constant total volume allow 2nd mark

(2 marks)

(Total 17 marks)

8080/9080 Chemistry Summer 2006

32

4.

Read through all of the plan first P

9

T

9

Mix two (or more) pairs (1) Record/measure temperature change (1) If no change (1) pair of alkalis (1) Correct identification of acid

9 i4

If candidate pre-supposes which is which zero (out of 4) here, but marks for second part are still available.

E

9

R

9

∆

9

Mix equal volumes of each acid and alkali (1) Repeat/done with each alkali (1) – Record/measure ∆T (1) – dependent on E9 being awarded Bigger change is for 2 M KOH (1) – dependent on E9 being awarded The second four marks are independent of the first four. 9 4w

If the second part is correctly done

(8 marks) End of Group 3

8080/9080 Chemistry Summer 2006

33

Materials Each candidate will require: (a) 0.5 g of a mixture of ammonium sulphate and magnesium sulphate, (approximately 50% of each by mass), labelled W. The identity of this mixture must not be disclosed to candidates; (b) 125 cm3 of aqueous sulphuric acid concentration 0.0480 mol dm–3, labelled Solution X; (c) 125 cm3 of aqueous sodium hydroxide of concentration 0.1 mol dm–3 labelled Solution Y. The concentration of this solution must not be disclosed to candidates; (d) 100 cm3 of sulphuric acid of concentration 1.0 mol dm–3 labelled Solution B; (e) 100 cm3 of sodium hydroxide of concentration 1.0 mol dm–3 labelled Solution A; (f) red litmus paper; (g) phenolphthalein indicator; (h) distilled water; (i) 5 cm3 of aqueous sodium hydroxide; concentration 1.0 mol dm–3 for Question 1; (j) 2 cm3 of aqueous barium chloride; concentration 0.05 mol dm–3; (k) 2 cm3 of aqueous hydrochloric acid; concentration 1.0 mol dm–3; (l) 8 cm3 of sodium hydrogencarbonate; concentration 0.5 mol dm–3.

8080/9080 Chemistry Summer 2006

34

Unit 6243/02 1

(a)

Gas ammonia/ NH3 Cation ammonium/ NH4+ If formula given must be correct Anion Sulphate / SO42− Formula of A (NH4)2SO4 IGNORE names

OR Hydrogen sulphate /HSO4− OR NH4HSO4

ALLOW (NH4)2CO3 or (NH4)2SO3 consequential on anion (b)

(4 marks)

Cation Sodium/ Na+ Gas Oxygen/ O2 Anion Cl−/ Chloride NOT chlorine or Cl Compound B Sodium chlorate OR sodium chlorate(III) / (V)/ (VII) OR NaClO3 / NaClO2 / NaClO4

ALLOW sodium chlorate(I) ALLOW NaClO/ NaOCl

ALLOW correct name or formula for B based on consequential cation, provided it gives a flame test. ALLOW correct name or formula for B based on consequential bromide anion.

(4 marks)

If chlorine given, can still get mark for B. If both name and formula of B given, they must agree Total 8 marks

8080/9080 Chemistry Summer 2006

35

2

(a)

(b)

Carbon dioxide lime water goes cloudy / milky/ white ppt (1) IGNORE lighted splint extinguished Sulphur dioxide (potassium) dichromate((VI))/chromate((VI)) (1) goes green (1) ALLOW goes blue OR (potassium) permanganate/ manganate((VII)) (1) goes colourless (1) IGNORE any reference to litmus going red Route I add solution of any soluble Group II compound (to both) (1) CO32− white precipitate (1) HCO3− no precipitate (1) White precipitate on boiling (1) Penalise once if an insoluble group II compound is used or solution not mentioned.

(3 marks)

Route II Use pH detection - pH meter/pH paper/ UI paper/ UI solution/ named indicator pKin >9 /phenolphthalein (1) CO32− pH 11-14 or correct colour (1) HCO3− pH 7-9 or correct colour NOT pH 7 alone (1) Boil/ heat pH changes to 11-14/ rises/ increases (1) Max 3 marks routes Boil/heat (1) NOT warm CO32− no CO2 (1) HCO3− correct test for CO2 NOT bubbles (1) OR pH detection, as for Route II above, and boil (1) CO32− no change (1) HCO3− rises NOT changes (1)

Notes • Allow magnesium ions/calcium ions/barium ions • If use magnesium/calcium max (3) • No marks for tests for CO2 with acid • Addition of any acid followed by tests on this solution (0) • Addition of acid followed by tests on a fresh solution, IGNORE acid

4 marks) Total 7 marks

8080/9080 Chemistry Summer 2006

36

3

(a) (b) (c)

Cannot be weighed as it is a gas ALLOW “measure” instead of “weigh”

(1 mark)

Solution will not be 250 cm3/ will not know exact volume/ standard solutions contain mols per dm3 of solution.

(1 mark)

(i)

2 and 3 (1) as these are within 0.2 cm3 of each other/ No.1 is too far away from the others/closest/most similar/concordant/ No. 1 is a rough titration (1) NOT consistent/better agreement

(ii)

30.4(0) (cm 3) consequential on part (i)

(2 marks) (1 mark)

(iii) 25.00 x 0.0500 = 1.25 x10-3 (mol) 1000

(1 mark)

(iv)

2 x (iii)

(1 mark)

(v)

Value from (iv) x 1000 / mean titre from (ii) (1) [Should be 2.5 x 10-3 x 1000 / 30.40] = 0.0822 mol dm-3 (1) – value, units and 3 sig figs NOTE • the value must be reasonable ie between 0.01 and 0.1 • if ‘1000’ omitted in parts (iii) and (v), penalise once only

8080/9080 Chemistry Summer 2006

37

(2 marks)

Total 9 marks

4

(a)

To make sure the decomposition/ reaction is complete / all the carbon dioxide has been given off. Reference to burning (0) NOT “maximum CO2”

(1 mark)

IGNORE significant figures in (b) and (c) (b)

(c)

(i)

2.2(0) (g)

(1 mark)

(ii)

2.20 = 0.05(00) mark is for ÷ 44 44

(1 mark)

(iii)

0.05(00)

(1 mark)

(iv)

5.75 0.0500

(v)

115 - (12 + 48) = 55 Consequential BUT answer must be sensible

(1 mark)

Molar mass error = 115 x 0.91 100 Consequential on (b)(iv) ALLOW a range of 2 x error

(1 mark)

(i)

(1) = 115 (g mol-1)

(1 mark)

= (±) 1(.05) (1)

(ii)

114 to 116 Consequential on (i)

(1 mark)

(iii)

54 to 56 Consequential on (ii)

(1 mark)

“Could be Mn or Fe” Consequential on (iii) MUST be metals and must give all possible in range

(1 mark)

(iv)

Total 10 marks

8080/9080 Chemistry Summer 2006

38

5

(a)

C=C / carbon carbon double bond (1) ALLOW alkene NOT just “double bond” -OH/ hydroxyl/ OH (1) NOT hydroxide NOT OH− NOT alcohol

(b)

(2 marks)

Isomers of C4H8O – these could be Unsaturated alcohols butanal or methylpropanal butanone Saturated cyclic alcohols Unsaturated ethers ALLOW cis-trans isomers Any carbon carbon double bonds must be shown NOTE penalise skeletal formulae with no H atoms once only (2 marks) Total 4 marks

8080/9080 Chemistry Summer 2006

39

6

(a)

(i)

To act as solvent/allow mixing /to dissolve halogenoalkanes/ increase miscibility

(ii)

It makes sure all solutions are the same temperature / heated equally

(1 mark)

(1 mark) (iii)

Too slow at room temp OR High activation energy OR (covalent) bond (energy) too strong to break at room temperature NOT to increase rate of reaction (1 mark)

(b)

Chlorine/ chloride: white, bromine/ bromide: cream and iodine/ iodide: yellow(1) Add ammonia (1) Cl: ppt soluble in dil ammonia Br: ppt soluble in conc ammonia ALLOW partial in dilute I: ppt insoluble in conc ammonia

(c)

(1)

(3 marks)

Use equal amounts (1) OR 1-bromo-2-methylpropane, AND 2-bromobutane, AND 2-bromo-2-methylpropane (1) – stand alone ALLOW names or structures IGNORE incorrect names if structures are correct at 60 OC / heat to same temp (between 40 and 75oC) (1) add (equal volume of) silver nitrate(solution) to each (1) observe time for ppt to be produced / order in which ppts form (1) Shortest time equivalent to fastest rate/vice versa (1) If add NaOH, only first 3 marks available

(6 marks)

If use KMnO4/K2CrO4/K2Cr2O7 allow halogenoalkane names mark only IGNORE statements of the expected result even if wrong Total 12 marks Total for paper: 50 marks

8080/9080 Chemistry Summer 2006

40

Unit 6244/01 1.

(a)

(i)

(ii)

(b)

(i)

(ii)

2Al + 3Cl2 → Al2Cl6 NOT AlCl3 IGNORE state symbols

(1 mark)

covalent (1) ALLOW polar covalent NOT giant covalent NOT partially covalent dative (covalent)/co-ordinate (1) SiCl4 + 2H2O → SiO2 + 4HCl ALLOW SiCl4 + 4H2O → Si(OH)4 + 4HCl ALLOW SiCl4 + 4H2O → H4 SiO4 + 4HCl ALLOW SiCl4 + 3H2O → H2 SiO3 + 4HCl

(2 marks)

(1 mark)

Fume cupboard (1) as HCl is irritant/harmful (1) NOT consequential on (b)(i) OR use small quantities/add slowly/with cooling (1) due to (highly) exothermic reaction (1) NOT “vigorous” These marks are freestanding within the answer pairs

(c)

(i) (ii)

Tetrahedral/tetrahedron/triangular (based) pyramid NOT pyramid

(2 marks) (1 mark)

lone pair on oxygen in water (1) ALLOW omission of oxygen or water THEN Either cannot attack C atom (1) because C atom too small / Cl atom too large (1) OR C (atom) has no low energy d/2d orbitals (1) ALLOW “no available d orbitals” So cannot form (dative covalent) bond (1) OR C (atom) has no low energy d/2d orbitals (1) ALLOW “no available d orbitals” C-Cl broken first (1) (3 marks)

If “no 3d orbitals” 2 max

8080/9080 Chemistry Summer 2006

41

(d)

oxidising (agent)/oxidant/can be reduced

(e)

tin is more stable in +4 than +2 oxidation state (1) MUST have comparison

(1 mark)

so Sn(IV) does not oxidise Cl−/HCl OR Sn(IV) not oxidising OR Sn(IV) not reduced (by Cl−/HCl) (1) OR SnO2 reacts as a base (therefore reaction II) ALLOW ions OR (reaction I does not work) because Sn(IV) more stable than Sn(II) (1) because energy required to promote (s) electrons is less than energy gained from bond formation (1) (2 marks)

If “reaction I more likely” (0)

Total 13 marks

8080/9080 Chemistry Summer 2006

42

2

(a)

(i) (ii)

CHI3 IGNORE correct name

(1 mark)

methyl ketone / CH3CO- (1) if also include CH3CH(OH) OR ethanol OR ethanal then (0)

(1 mark)

(iii) structure: (double bond must be shown)

O (CH3)2CHC

CH3

(1)

methylbutanone OR 3-methylbutan(-2-)one (1) ALLOW 2-methylbutan(-3-)one Name only scores on a correct structure NOT consequential on structure (b)

(i) (ii)

(c)

(d)

aldehyde(s) IGNORE carbonyl

(1 mark)

copper(I) oxide/Cu2O /cuprous oxide NOT copper oxide

(1 mark)

any strong acid ALLOW HCl/conc H2SO4 NOT hydrogen chloride ACCEPT name or formula If other reagents with the acid eg K2Cr2O7 (0) (i)

(1 mark)

effervescence/fizzing/bubbles NOT gas evolved NOT CO2 evolved OR solid dissolves/disappears NOT solution formed

(ii)

(2 marks)

(1 mark)

CH3(CH2)3COOH + NaHCO3 → CH3(CH2)3COONa + H2O + CO2 correct formula of pentanoic acid (1) balanced equation (1) ALLOW CH3(CH2)3CO2H and CH3(CH2)3CO2Na ALLOW –COO−Na+ but not ⎯ O ⎯ Na RCOOH + NaHCO3 → RCOONa + H2O + CO2 - Scores 2nd mark IGNORE R OR R.COOH + HCO3¯ → RCOO¯ + H2O + CO2

(2 marks) Total 10 marks

8080/9080 Chemistry Summer 2006

43

3

(a)

(i) (ii)

(b)

(i) (ii)

- lg (0.05) = 1.3(0) IGNORE sig figs from this point on in this question

(1 mark)

[OH−] = 1 x10-14 / 0.05 = 2 x10-13 (mol dm-3) OR via pOH Correct answer with no working (1)

(1 mark)

Ka = [H2PO4−][H3O+]/[H3PO4] NOT using H+ instead of H3O+

(1 mark)

[H3O+] = 10-1.20 = 0.063 (mol dm-3) (1) 0.0632 NOT consequential on (b)(i) 0.500 – 0.063 (1) = 9.08 x10-3 (1) mol dm-3 (1) = 9.11 x10-3 if [H3O+] not rounded

Ka =

ALLOW Ka = 0.0632 (1) 0.500 = 7.94 x10-3 (1) mol dm-3 (1) = 7.96 x 10-3 if [H3O+] not rounded ALLOW consequential marking on numerical errors Correct answer with units and some working (4) (4 marks) (c)

(i) (ii)

(d)

Assign the terms ‘acid/base’ (1) link the pairs (1)

(2 marks)

presence of H+ from the first dissociation keeps equilibrium to left /suppresses ionisation

(1 mark)

Bromocresol green (1) pKin/range/colour change (of indicator) lies in vertical section OR For alternative indicators pKin/range/colour change (of indicator) lie outside vertical section (1)

(2 marks) Total 12 marks

8080/9080 Chemistry Summer 2006

44

4

(a)

(i)

enthalpy/heat/energy change/produced [NOT “required”] when one mole of gaseous ions (1) are dissolved in excess water/ to infinite dilution (1)

(ii)

(2 marks)

Bonds formed / attraction between (1) cation and δ- O/lone pair (in water) OR anion and δ+ H (in water) (1) (2 marks)

If bond between anion and cation (0) (b)

as magnesium has a much smaller ion (than barium ion) (1) and has same charge OR charge shown (1) so stronger attraction between ions (1) ALLOW stronger bonds between ions “charge density” scores 1 (out of first 2 marks) IGNORE references to polarisation and covalency of the ions

(c)

(i)

(3 marks)

cycle: for each labelled arrow joining correct species. Lattice Energy Mg(OH) 2(s)

Mg2+(g) (+) 2OH−(g)

∆Hsolution

∆Hhydration

Mg2+(aq) (+) 2OH-(aq)

Species and stoichiometry (1) State symbols (1) Labels appropriate to direction of arrows (1) ALLOW numerical values ALLOW cycles using −LE (ii)

∆Hsolution = − LE + ∑∆Hhydration

OR numbers (1)

+5 kJ mol-1 (1) Consequential on candidate’s cycle eg calculation from cycle with one OH− giving +555 kJ mol-1 (2) BUT correct answer with working (2) even if the (c)(i) cycle is wrong

8080/9080 Chemistry Summer 2006

(3 marks)

45

(2 marks)

(d)

Calculation of ∆Hsolution of Ba(OH)2 as -55 kJ mol-1 OR LE down by 675 but ∆Hhydration down by 615 ALLOW LE down but ∆Hhydration down by less (1) ∴ ∆Hsolution is more exothermic (1) ∴ solubility is greater (1) 2nd mark dependent on 1st 3rd mark dependent on 2nd

(3 marks)

ALLOW consequential marking if ∆Hsolution less exothermic Total 15 marks

8080/9080 Chemistry Summer 2006

46

5.

(a)

(i)

chiral carbon marked as one to right of −C6H4−

(ii)

Has non-superimposable mirror images OR no plane/centre of symmetry NOT four different groups about the C atom on its own NOT asymmetric C atom

(b)

(i)

(ii) (d)

(2 marks)

PCl5 /PCl3 /SOCl2 OR names (1) phosphorus(V) oxide /pentoxide /P4O10/P2O5 (1) Nucleophilic substitution

(2 marks) (1 mark)

bromine (1) NOT bromine water (aqueous) sodium hydroxide/ potassium hydroxide (1) OR LiAlH4 (1) then acid/water (1) OR H2 (1) Ni/Pt/Pd (1) OR Na (1) ethanol (1) 2nd reagent depends on the 1st Incorrect 2nd reagent negates 1st mark

(e)

(1 mark

rotate (the) plane (of plane) polarised (monochromatic) light (1) (equally) in opposite directions (1) OR pass polarised light through sample (1) rotate the plane (equally) in opposite directions (1)

(c)

(1 mark)

(i)

O

(2 marks)

O

R C OCH2CH3 / R C OC2H5 Double bond must be shown Full structural formula must have H’s (ii)

reaction with A is faster/does not need a catalyst/does not need heating (1) and gives higher yield/not reversible/not equilibrium/goes to completion (1)

8080/9080 Chemistry Summer 2006

(1 mark)

47

(2 marks)

(f)

Any named strong acid solution (1) ALLOW formulae with indication of state NOT (conc) H2SO4 NOT sulphuric acid heat under reflux (1) – NOT stand alone but can score if (conc) H2SO4 given as the acid ALLOW “heat/reflux” OR Any named strong aqueous alkali (heat) (1) ALLOW formulae with indication of state Then add named strong acid (1) (2 marks)

ALLOW formulae

Total 14 marks

8080/9080 Chemistry Summer 2006

48

6.

(a)

Kc = [H2]2 [S2] [H2S]2 MUST be square brackets

(1 mark)

(b) Number of moles at equilibrium

H2S (0.350)

Concentration

0.0175

H2 0.150 (1) 0.0075

S2 0.075 (1) 0.00375

(1) ie ÷ 20 Kc = [0.0075]2[0.00375] [0.0175]2 = 6.9 x 10-4 (1) award only if concentration used

mol dm-3 (1)

ALLOW consequential marking on (a) and numerical errors PENALISE anything other than 2SF in final answer Units consequential on the Kc expression used (c)

(5 marks)

Kc does not change (1) Change in pressure increases value of numerator more than denominator/quotient bigger, so no longer at equilibrium (1) ALLOW fewer (gas) molecules on LHS Equilibrium shifts to restore equality (of quotient) with Kc OR Equilibrium shifts to LHS (1) (3 marks)

If Kc changes max 1 (d)

(i)

no change

(1 mark)

(ii)

Increases If reason given, must be correct

(1 mark) Total 11 marks Total for paper 75 Marks

8080/9080 Chemistry Summer 2006

49

8080/9080 Chemistry Summer 2006

50

Unit 6245/01 1.

(a)

(i)

Yellow/orange precipitate (allow red/any shades of red)

(ii)

(1 mark)

NO2 H H

H

H N O2

C C C N N H H C

N

(1)

H C

N

Must be formed by C atom from the C = O group

(2 marks)

rest of molecule correct (1) (b)

Hydrogen nuclei OR hydrogen atoms OR hydrogen(s) OR protons (1) in (three) different environments (may be shown by diagram) (1) Ratio 2:1:1 (1) Any reference to fragments or bonds scores zero

8080/9080 Chemistry Summer 2006

51

(3 marks)

(c)

(i)

EITHER H2C

(1)

CH C

O (:) CH2

O

CH

C

CN

(1) for intermediate

H

H

(1) (: )CN (1) O (:) CH2

CH

C

H

OH

CN

CN

CH2

H

CH

C

CN

H

+ (:) CN Lone pairs not essential. Arrow may start from minus of O

• • • • • • •

8080/9080 Chemistry Summer 2006

The intermediate is not consequential on their first step The minus of the cyanide ion can be on either the C or the N The arrow can start from the minus of –CN in step 1 (but not from the minus of CN-) and can start from the minus of O- in step 2 The arrow from the bond must not go past the O atom Lone pairs not essential Single step addition of HCN scores zero Autoionisation of C=O can only score the last two marks ie max 2

52

OR (1) H2C

O(:)

CH C

CH 2

O

CH

H

C

CN

(1) for intermediate

H

(1)

(:)CN

(1) O (:) CH 2

CH

OH

H

C

CH 2

CN

CH

• • • • (ii) (d)

CN

H

H

• • •

C

The intermediate is not consequential on their first step The minus of the cyanide ion can be on either the C or the N The arrow can start from the minus of –CN in step 1 (but not from the minus of CN-) and can start from the minus of O- in step 2 The arrow from the bond must not go past the O atom Lone pairs not essential Single step addition of HCN scores zero Autoionisation of C=O can only score the last two marks ie max 2

(1 mark)

Nucleophilic addition Stand alone

(i) H

H

H

C

C

(4 marks)

O H

C

H

H

C

C

O C

H

(δ+)

H

H

H

(1) for intermediate

(δ-)

(:) Br

Br

(1) for both arrows H H

C

H C

H

O

H O

H

C

C

C

C H

H

H

H

Br

(3 marks)

(:) Br

(1) for arrow Note: If Br is on the wrong carbon atom, only third mark available (ii)

Electrophilic addition Stand alone

8080/9080 Chemistry Summer 2006

(1 mark)

53

(e) QWC*

•

C = O is a polar bond OR O more electronegative than C (1)

•

C = C has high electron density OR C = C is electron rich (1) IGNORE “C=C is non-polar” and references to ∏ bond

•

Cδ+ can be attacked by a nucleophile OR (C in) C = O can be attacked by nucleophile (3 marks) OR C = C attacked by electrophile (1) Total for question: 18 marks

8080/9080 Chemistry Summer 2006

54

2

(a)

3d [ Ar ]

4s

↿ ↿ 3d

[ Ar ]

(1) 4s

↿ ↿

(1)

(2 marks)

Allow instead of ↿ and instead of ⇂ (b)

Forms ion(s) which have a partially OR an incompletely filled d-(sub)shell OR dorbital(s)

(c)

(i)

Dative (covalent) OR co-ordinate (1) Covalent (1)

(2 marks)

(ii)

[ Ni ( H 2 O) 6 ] 2+ + 2 NH 3 → [ Ni (OH ) 2 ( H 2 O) 4 ] + 2 NH 4+

(iii)

OR [ Ni ( H 2 O ) 6 ] 2+ + 2 NH 3 → Ni (OH ) 2 + 4 H 2 O + 2 NH 4+ OR [ Ni ( H 2 O ) 6 ] 2 + + 2OH − → [ Ni (OH ) 2 ( H 2 O ) 4 ] + 2 H 2 O OR [ Ni ( H 2 O ) 6 ] 2 + + 2OH − → Ni (OH ) 2 + 6 H 2 O IGNORE state symbols IGNORE missing square brackets in any formula + H removed (by NH3 OR OH-)(1)

(iv) (v)

(1 mark)

From (H2O) ligands (1) NOT just from “complex” Ligand exchange OR ligand replacement OR ligand substitution [ Ni (OH ) 2 ( H 2 O ) 4 ] + 6 NH 3 → [ Ni ( NH 3 ) 6 ] 2 + + 2OH − + 4 H 2 O

(1 mark)

(2 marks)

(1 mark)

OR

Ni (OH ) 2 + 6 NH 3 → [ Ni ( NH 3 ) 6 ] 2 + + 2OH − Allow formation of [ Ni ( NH 3 ) 4 ]2 + OR [ Ni ( NH 3 ) 4 ( H 2 O) 2 ] 2 + cation formed (1) (2 marks)

balancing equation (1)

8080/9080 Chemistry Summer 2006

55

(d) QWC*

d-orbitals split (in energy) by ligands (1) ALLOW d-sublevel absorbs light (in visible region) (1) NOT “uv light” electron is promoted OR electron moves to a higher energy level (1)

(3 marks)

Any mention of emission of light can only score 1st mark Total for question: 14 marks

8080/9080 Chemistry Summer 2006

56

3

(a)

(b)

Rate of decrease OR rate of change in concentration of reactants OR rate of increase OR rate of change in concentration of products. OR change in concentration of reactants with time OR change in concentration of products with time (1) NOT just ‘amount’ Sum of the powers to which the concentrations are raised in the rate equation OR number of species involved in (up to and including) the rate determining step OR sum of partial orders if illustrated with a general rate equation (1) ‘Sum of the partial orders’ alone does not score. (i)

(ii) (iii)

(2 marks)

Both orders correct (1) EITHER Expt 1 + 3: double [A], doubles rate so order 1 (1) Expt 1 + 2: double [B], four x rate so order 2 (1) OR Double [A] keeping [B] constant doubles rate so order 1 (1) Double [B] keeping [A] constant four x rate so order 2 (1) Omission of experiment number or keeping a concentration constant to be penalised ONCE only (1) Rate = k [A] [B]2. Mark consequentially on (i) k =

rate [A] [B]2

= =

(1 mark)

0.00200 0.100 x (0.100)2 2(.00) (1) mol-2 dm6 min-1 (1)

Consequential on their rate equation in (ii) Use of experiment 2 or experiment 3 can score max (1)

8080/9080 Chemistry Summer 2006

(3 marks)

57

(2 marks)

(iv)

}

A + B → AB rds

AB + B → AB2 fast

AB2 + B → AB3 OR B + B → B2 rds

A + B2 → AB2

}

fast

AB2 + B → AB3

(1) for first two equations (1)

(1) for first two equations (1)

OR slow / rds

A + 2 B → AB2 fast

AB2 + B → AB3

(1) (1)

(3 marks)

Identifying slow(est) OR rate determining step by appropriate notation (1) SN1 or SN2 scores zero

8080/9080 Chemistry Summer 2006

58

(c)

(i) 3.0

1 10 3 −1 x K T 3.1

3.2

3.3

-2.0 -3.0 log10 k -4.0

-5.0

(2 marks) All points plotted accurately (1) with best-fit straight line drawn (1) (ii) − 4.25 − (−3.10) 0.00330 − 0.00310 − 1.15 = 0.00020 = -5750 (K) (1) ALLOW = -5450 to -6050 (K) but MUST have a negative sign ALLOW if gradient is left as a correct fraction such as -1.15 0.00020

Gradient eg =

Ea

= (+)5750 x 2.30 x 8.31 = (+)110 kJ mol-1 / (+) 110000 J mol-1 (1) ALLOW = (+)104 to (+)116 kJ mol-1 (2 marks) IGNORE S.F. nd (2 mark consequential on gradient, but value of Ea must be in correct units) Total for question: 15 marks

8080/9080 Chemistry Summer 2006

59

4

(a)

(i)

White precipitate OR white suspension OR white solid (1 mark)

(ii)

2,4,6-tribromophenol (1) rest of equation if for formation of a tribromophenol (1)

C 6 H 5 OH + 3Br2 → C 6 H 2 Br3 OH + 3HBr

(2 marks)

scores (1)

(iii) O O

C

(1 mark) CH3

(iv)

(b)

(c)

C = O in ester must be shown C (atom) is (very) δ+ because Cl highly electronegative OR Cl electron withdrawing (1) IGNORE references to oxygen

(so C atom) susceptible to nucleophilic attack OR (so C atom) strongly electrophilic (1) IGNORE references to activation energy Sn and conc hydrochloric acid (accept conc HCl) OR Fe and conc hydrochloric acid (accept conc HCl) IGNORE any references to NaOH IGNORE references to Fe or Sn as a catalyst (i) • Sodium nitrite OR NaNO2 OR sodium nitrate(III) (1) NOT JUST HNO2 • Hydrochloric acid OR dilute sulphuric acid OR aqueous sulphuric acid ACCEPT HCl if qualified. Do not accept conc. sulphuric acid Only award the hydrochloric acid mark if NaNO2 or KNO2 or HNO2 given as co-reagent (ii) Below 0°C : reaction too slow (1)

(iii)

Above 5°C : product decomposes OR diazonium ion decomposes (1) NOT HNO2 decomposes

OR -Oinstead of –OH group

8080/9080 Chemistry Summer 2006

60

(2 marks) (1 mark)

(2 marks)

(2 marks)

(1 mark)

(iv) QWC*

Dissolve in minimum volume of boiling solvent OR dissolve in minimum volume of hot solvent(1) NOT JUST “small volume” [ALLOW any specified solvent including water] Filter hot OR filter through heated funnel (1) Cool or leave to crystallise (1) Filter (under suction) (1) Wash solid with cold solvent (and leave to dry) OR wash solid with small volume of solvent (and leave to dry) (1)

(5 marks)

Total for question: 17 marks

8080/9080 Chemistry Summer 2006

61

5

(a)

(i)

EITHER ∆Eθ = (+) 0.15 (V) OR Eθ (MnO4-/ Mn2+) more positive or greater than Eθ (Cl2/ Cl ); accept reverse argument (1) (so) MnO4- reacts with Cl- OR Cl- ions form Cl2 OR KMnO4 reacts with HCl (1) OR 2MnO4 - + 16H+ + 10Cl- →- 2Mn2+ + 8H2O + 5Cl2 (1) Eθ = (+) 0.15(V) (1)

(ii)

(b)

(i)

stated colour change of colourless to (pale) pink NOT purple OR stays (pale) pink OR pink to colourless OR first excess of (coloured) manganate((VII)) IGNORE “self-indicating” IGNORE references to Mn2+ (Multiply iron half-equation by five to) cancel out electrons OR balance electrons

(ii)

(2 marks)

(1 mark)

(1 mark)

−

Moles MnO4 = 0.0200 x 20.10 1000

−

= 0.000402 mol MnO4

(1)

2+

Moles Fe per 25.0 cm3 = 5 x 0.000402 2+ = 0.00201 mol Fe (1) Moles Fe2+ per 200 cm3 = 0.00201 x

2+ 200 mol Fe 25

= 0.01608 mol Fe Mass of FeSO4 . 7H2O Percentage purity

2+

(1)

= 0.01608 x 278 = 4.47g or via concentrations (1) = 4.47 x 100% 6.00 = 74.5% (1) ALLOW 74.7% / 75%

Correct answer + working (5) ALLOW 2 or more sig figs If start by dividing 6.00 , and final answer is incorrect, candidate can 278 access first three marks only. If third step omitted, answer 9.3% OR 9.33% OR 9.4%

8080/9080 Chemistry Summer 2006

62

(5 marks)

(c)

(i)

Eθ = + 1.46 - ( - 0.13) = ( + ) 1.59 (V) Correct answer alone (1)

(ii)

PbSO4 precipitated (1) [H+(aq)] not 1 mol dm-3 (1) [Pb2+ (aq)] not 1 mol dm-3 (1) the conditions (in the car battery) are not standard (1)

(1 mark)

any one of these (1 mark)

“ temperature non-standard” alone or “not 1 atm pressure” alone does not score Total for question: 11 marks Total for paper: 75 marks

8080/9080 Chemistry Summer 2006

63

8080/9080 Chemistry Summer 2006

64

1

Fe3+ /Fe(OH)3 /iron(III) hydroxide/iron(III) ions (1)

Any brown precipitate (1)

If “soluble in acid” (0), any inference (0)

Inference must follow any coloured ppt and insoluble in acid /HCl observation If a near miss for 2nd observation mark eg “did not dissolve”, inference mark may be allowed

Inference Sulphate/SO42−/BaSO4/barium sulphate (1) IGNORE HSO4− If word and formula given, both must be correct

2+

65

FeSO4 / FeSO4.7H2O – NOT stand alone, there must be a logical progression from inferences

insoluble in acid/HCl OR no change in acid/HCl (1)

Observations white ONLY precipitate (1)

8080/9080 Chemistry Summer 2006

(d)

(c)

Oxidised (1) – dependent on 1st inference mark

Insoluble in excess (1)

MUST be on addition of H2O2 NOT aerial oxidation

Inferences Fe(OH)2 /iron(II) hydroxide /Fe /iron(II) ions (1)

Observations Any green precipitate (1)

ACCEPT words or formulae

transition metal ion/compound OR any two from: Nickel/chromium(III)/copper/iron(II)/vanadium(III) ion/compound (1)

(b)

Inference

Observation any green (solution) (1)

(a)

Unit 6246/01A Practical Test Group 1

(1 mark)

(3 marks)

(6 marks)

(2 marks)

KCl

Lilac/mauve (1) ALLOW purple

Observation

Soluble in ammonia/colourless solution (1)

Observations Any white precipitate (1) NOT “cream” on its own

8080/9080 Chemistry Summer 2006

(g)

(f)

(e)

Inference

66

K /potassium ion /potassium / K (1)

+

Inference Chloride / Cl−/ AgCl (1) – both observations needed to get this mark

Total 18 marks

(1 mark)

(2 marks)

(3 marks)

2.

Observation

58 (1)

m/e value of molecular ion

Fruity/sweet/glue smell /any nail varnish (1) NOT pungent

8080/9080 Chemistry Summer 2006

(d)

(c)

Observation

(b)

Any red precipitate (1)

Observation Yellow/orange precipitate (1)

(a)

O

C2H5C O

H

67

Ester (1) (D is an) alcohol (1)

Inferences

(1) IGNORE any +ve charge, BUT a −ve charge (0) ALL Hs must be shown If ketone inferences in (b) credit propanone structure

CH3CH2C

H

Structural formula

If no red ppt/no change as observation, ALLOW inferences ketone/“not aldehyde”

Aldehyde / CHO / “not ketone” (1)

Inference

Inference Carbonyl / C=O / both “aldehyde and ketone” (1)

(3 marks)

(2 marks)

(2 marks)

(2 marks)

OR (Lucas test) Concentrated HCl + ZnCl2

68

Iodine + sodium hydroxide (solutions) OR potassium iodide + NaOCl OR Acidified dichromate ions/acidified potassium dichromate/H++Cr2O72− then

Fehlings or Tollens or Ammoniacal AgNO3 or Test for acidity or 2,4-DNP

“Primary or secondary”/ “1o or 2o”/◦ “not tertiary” (alcohol) (1) NOT Aldehyde

Inferences Redox /oxidation/Cr2O72− is reduced NOT just “reduction” (1)

CH3CH2CH2CH2OH (1) CH3CH(OH)CH2CH3 (1) ALLOW C2H5 NOT C3H7 N.B Missing carbon Hs should only be penalised once (ie either here or in (c))

8080/9080 Chemistry Summer 2006

(ii)

(i)

(f)

Structures (not necessarily full structural)

Observation (Orange to) green/blue-green/blue/brown (1)

(e)

(1 mark)

(2 marks)

(3 marks)

69

ALLOW observation marks for “near-miss” reagents in (ii) eg “iodoform test”, no “acidified”, no “then”

OR (From Lucas test) butan-2-ol goes cloudy first/quickly, butan-1-ol goes cloudy slowly/no cloudiness

OR Correct results from Fehlings/Tollens/test for acidity/2,4-DNP

Yellow precipitate with butan-2-ol isomer (1) No precipitate / No change with butan-1-ol isomer (1)

8080/9080 Chemistry Summer 2006

(iii)

(Total 17 marks)

(2 marks

3.

IGNORE “impurities” IGNORE “hard to judge bubbles” IGNORE “hard to read thermometer” IGNORE “distillation”

“Not enough temperature control”/heating too rapid

Temp of liquid may not be same as temp of water Inaccurate thermometer

70

Place thermometer directly in E /cool down more slowly Replace by more accurate thermometer / digital thermometer Repeat to obtain a second pair of readings

Consequential improvement (1)

Boiling temperatures are too close together

(ii)

Reason (1)

Identifying E as the ester with Table 2 boiling temperature closest to mean of candidate’s recorded temperatures. [Mean of candidate’s rising and falling temperatures, calculated by examiner, and recorded to 1 dp next to Table 2]

(i)

International Centres – Comparison with Supervisor’s mean temperature then ± 1 oC (2) ± 2 oC (1) Write mean used for comparison on script “S = …..” near Table 2

For either temperature 77 ± 1 oC (2) 77 ± 2 oC (1) [Put the ticks below the temperature used for accuracy mark]

For both temperatures within 2 oC of each other (2) within 3 oC (1) IGNORE decimal points here [Put the ticks above Table 1]

E is ethyl ethanoate: boiling point confirmed as 77 oC

8080/9080 Chemistry Summer 2006

(c)

(b)

(a)

(Total 8 marks)

(2 marks)

(1 mark)

(1 mark)

(4 marks)

4.

Two pairs will give a ppt, one pair will not (1) NH3 identified with reason (1)

AlCl3 and ZnCl2 both form white precipitates (1)

NH3 gives no precipitate (1)

Add excess NH3 (1) Filter/centrifuge off precipitate (1) (of Al(OH)3)

71

END of 6246/01A

If tested for NH3 by smell (0) or if assumed NH3 then may award final 2 marks IGNORE formulae throughout

Zn precipitate dissolves in NH3 OR Al precipitate does not dissolve in NH3 (1)

Add excess NH3 to both AlCl3 and ZnCl2 /to precipitates(1)

Clear explanation of mixing in pairs (there are three combinations eg A+B, A+C, B+C) (1) NOT assumption of identities

Alternative for 1st three marks

Add NaOH to each unknown (1)

8080/9080 Chemistry Summer 2006

(b)

(a)

Total 7 marks

(2 marks)

(5 marks)

Materials Each candidate will require: (a)* 1.0 g of hydrated iron(II) sulphate, FeSO4.7H2O, in a stoppered specimen tube labelled A. The identity of this compound is not to be disclosed to candidates; (b)* 1.0 g of potassium chloride, KCl, in a stoppered specimen tube labelled B. The identity of this compound is not to be disclosed to candidates; (c)* 3 cm3 of propanal in a stoppered test tube labelled C. The identity of this compound is not to be disclosed to candidates; (d)* 3 cm3 of butan-1-ol in a stoppered test tube labelled D. The identity of this compound is not to be disclosed to candidates; (e)* 1 cm3 of ethanoic acid in a stoppered test tube labelled ethanoic acid; (f)* 1 cm3 of ethyl ethanoate in a stoppered ignition tube labelled E. The identity of this compound is not to be disclosed to candidates; (g) 5 cm3 of aqueous sodium hydroxide; concentration approximately 0.5 mol dm–3; (h) 2 cm3 of aqueous nitric acid; concentration approximately 2.0 mol dm–3; (i) 5 cm3 of aqueous ammonia; concentration approximately 2.0 mol dm–3; (j) 5cm3 of aqueous hydrochloric acid; concentration approximately 2.0 mol dm–3; (k) 5 cm3 of aqueous sulphuric acid; concentration approximately 1.0 mol dm–3; (l) 5 cm3 of aqueous barium chloride; concentration approximately 0.2 mol dm–3; (m) 2 cm3 of aqueous silver nitrate; concentration approximately 0.05 mol dm–3; (n) 3 cm3 of approximately 10 vol aqueous hydrogen peroxide; (o) 5 cm3 of 2,4-dinitrophenylhydrazine solution. This may be prepared by adding 0.1 g of the solid reagent to a mixture of 45 cm3 of water and 5 cm3 of concentrated hydrochloric acid, stirring and filtering if necessary. Alternatively, centres may prepare this reagent using their own procedure providing the reagent gives a positive result with propanal;

8080/9080 Chemistry Summer 2006

72

1.

Inference

If “soluble in acid” (0), any inference (0)

If a near miss for 2nd observation mark eg “did not dissolve”, inference mark may be allowed

Inference must follow any coloured ppt and insoluble in acid /HCl observation

Inference Sulphate/SO42−/BaSO4/barium sulphate (1) IGNORE HSO4− If word and formula given, both must be correct

Inference Co(OH)2 / cobalt(II) compound / Co2+ (1)

Cobalt compound/ Co OR transition metal ion/compound (1) IGNORE Mn2+

2+

73

CoSO4 / CoSO4 .7H2O – NOT stand alone, there must be a logical progression from inferences

insoluble in acid/HCl OR no change in acid/HCl (1)

Observations white ONLY precipitate (1)

8080/9080 Chemistry Summer 2006

(d)

(c)

Observations Any blue precipitate (1)

(b)

turns pink/red (1)

Observation red/pink (solution) (1)

(a)

Unit 6246/01B Practical Test Group 2

(1 mark)

(3 marks)

(3 marks)

(2 marks)

Observation

NaI

Yellow (1) ALLOW orange

8080/9080 Chemistry Summer 2006

(h)

(g)

Observations Yellow/any brown solution (1) IGNORE precipitate

(f)

Blue/black/blue-black (1)

Observation Any yellow precipitate (1) NOT “cream” on its own NOT “white” on its own

(e)

Inference

74

Na+ /sodium ion /sodium /Na (1)

(I−) oxidised (1) to Iodine / I2 (1) OR 2I− → I2 + 2e− (2) Inference

Inferences

OR “Iodide/I−/AgI or bromide/Br−/AgBr” – BUT must follow correct “mixed” observation

Iodide/I−/AgI (1)

Total 18 marks

(1 mark)

(2 marks)

(4 marks)

(2 marks)

2.

Observation

58 (1)

m/e value of molecular ion

Fruity/sweet/glue smell /any nail varnish (1) NOT pungent

8080/9080 Chemistry Summer 2006

(d)

(c)

Observation

(b)

Silver mirror/black precipitate (1)

Observation Yellow/orange precipitate (1)

(a)

O

H C2H5C O

H

75

Ester (1) (J is an) alcohol (1)

Inferences

(1) IGNORE any +ve charge, BUT a −ve charge (0) ALL Hs must be shown If ketone inferences in (b) credit propanone structure

CH3CH2C

Structural formula

If no silver mirror/black ppt/no change as observation, ALLOW inferences ketone/“not aldehyde”

Aldehyde / CHO / “not ketone” (1)

Inference

Inference Carbonyl / C=O / both “aldehyde and ketone” (1)

(3 marks)

(2 marks)

(2 marks)

(2 marks)

Inferences is reduced

OR (Lucas test) Concentrated HCl + ZnCl2

76

Iodine + sodium hydroxide (solutions) OR potassium iodide + NaOCl OR Acidified dichromate ions/acidified potassium dichromate/H++Cr2O72− then

Fehlings or Tollens or Ammoniacal AgNO3 or Test for acidity or 2,4-DNP

“Primary or secondary”/ “1o or 2o”/◦ “not tertiary” (alcohol) (1) NOT Aldehyde

Redox NOT just “reduction” (1)

/oxidation/Cr2O72−

CH3CH2CH2OH (1) CH3CH(OH)CH3 (1) ALLOW C2H5 NOT C3H7 N.B Missing carbon Hs should only be penalised once (ie either here or in (c))

8080/9080 Chemistry Summer 2006

(ii)

(i)

(f)

Structures (not necessarily full structural)

Observation (Orange to) green/blue-green/blue/brown (1)

(e)

(1 mark)

(2 marks)

(3 marks)

77

ALLOW observation marks for “near-miss” reagents in (ii) eg “iodoform test”, no “acidified”, no “then”

OR (From Lucas test) propan-2-ol goes cloudy first/quickly, propan-1-ol goes cloudy slowly/no cloudiness

OR Correct results from Fehlings/Tollens/test for acidity/2,4-DNP

Yellow precipitate with propan-2-ol isomer (1) No precipitate / No change with propan-1-ol isomer (1)

8080/9080 Chemistry Summer 2006

(iii)

(Total 17 marks)

(2 marks

3.

IGNORE “impurities” IGNORE “hard to judge bubbles” IGNORE “hard to read thermometer” IGNORE “distillation”

“Not enough temperature control”/heating too rapid

Temp of liquid may not be same as temp of water Inaccurate thermometer

78

Place thermometer directly in K /cool down more slowly Replace by more accurate thermometer / digital thermometer Repeat to obtain a second pair of readings

Consequential improvement (1)

Boiling temperatures are too close together

(ii)

Reason (1)

Identifying K as the ester with Table 2 boiling temperature closest to mean of candidate’s recorded temperatures. [Mean of candidate’s rising and falling temperatures, calculated by examiner, and recorded to 1 dp next to Table 2]

(i)

International Centres – Comparison with Supervisor’s mean temperature (check questionnaire) then ± 1 oC (2) ± 2 oC (1) Write mean used for comparison on script “S = …..” near Table 2

For either temperature 79 ± 1 oC (2) 79 ± 2 oC (1) [Put the ticks below the temperature used for accuracy mark]

For both temperatures within 2 oC of each other (2) within 3 oC (1) IGNORE decimal points here [Put the ticks above Table 1]

K is methyl propanoate: boiling point confirmed as 79 oC

8080/9080 Chemistry Summer 2006

(c)

(b)

(a)

(Total 8 marks)

(2 marks)

(1 mark)

(1 mark)

(4 marks)

4.

Two pairs will give a ppt, one pair will not (1) NH3 identified with reason(1)

AgNO3 and Pb(NO3)2 both form white precipitates (1)

NH3 gives no precipitate (1)

OR add excess ammonia (1) Filter/centrifuge off precipitate (1) (of Pb(OH)2)

Add NaCl followed by NH3 (1) Filter/centrifuge off precipitate (1) (of PbCl2)

79

End of 6246/01B

If tested for NH3 by smell (0) or if assumed NH3 then may award final 2 marks IGNORE formulae throughout

Ag precipitate dissolves in NH3 OR Pb precipitate does not dissolve in NH3 (1)

Add NH3 to both precipitates/add excess NH3 to both solutions (1)

Clear explanation of mixing in pairs (there are three combinations eg A+B, A+C, B+C) (1) NOT assumption of identities

Alternative for 1st three marks

Add NaCl to each unknown (1)

8080/9080 Chemistry Summer 2006

(b)

(a)

Total 7 marks

(2 marks)

(5 marks)

Materials Each candidate will require: (a)* 1.0 g of hydrated cobalt(II) sulphate, CoSO4.7H2O, in a stoppered specimen tube labelled F. The identity of this compound is not to be disclosed to candidates; (b)* 1.0 g of sodium iodide, NaI, in a stoppered specimen tube labelled G. The identity of this compound is not to be disclosed to candidates; (c)* 3 cm3 of propanal in a stoppered test tube labelled H. The identity of this compound is not to be disclosed to candidates; (d)* 3 cm3 of propan-1-ol in a stoppered test tube labelled J. The identity of this compound is not to be disclosed to candidates; (e)* 1 cm3 of ethanoic acid in a stoppered test tube labelled ethanoic acid; (f)* 1 cm3 of methyl propanoate in a stoppered ignition tube labelled K. The identity of this compound is not to be disclosed to candidates; (g) 10 cm3 of aqueous sodium hydroxide; concentration approximately 0.5 mol dm–3; (h) 2 cm3 of aqueous nitric acid; concentration approximately 2.0 mol dm–3; (i) 5 cm3 of aqueous hydrochloric acid; concentration approximately 2.0 mol dm–3; (j) 5 cm3 of aqueous sulphuric acid; concentration approximately 1.0 mol dm–3; (k) 5 cm3 of aqueous barium chloride; concentration approximately 0.2 mol dm–3; (l) 3 cm3 of approximately 10 vol aqueous hydrogen peroxide; (m) 5 cm3 of 2,4-dinitrophenylhydrazine solution. This may be prepared by adding 0.1 g of the solid reagent to a mixture of 45 cm3 of water and 5 cm3 of concentrated hydrochloric acid, stirring and filtering if necessary. Alternatively, centres may prepare this reagent using their own procedure providing the reagent gives a positive result with propanal; (n) 5 cm3 of aqueous silver nitrate; concentration approximately 0.2 mol dm–3. This solution will be used in both a halide and a silver mirror test; (o) access to a bottle of concentrated sulphuric acid; (p) 60 cm3 of approximately 1.0 mol dm–3 aqueous sodium carbonate;

8080/9080 Chemistry Summer 2006

80

Observations white ONLY precipitate (1)

(c)

(d)

Observations Green precipitate (1) Insoluble in excess (1)

(b)

If “soluble in acid” (0), any inference (0)

Inference must follow any coloured ppt and insoluble in acid /HCl observation If a near miss for 2nd observation mark eg “did not dissolve”, inference mark may be allowed

Inferences Sulphate/SO42−/BaSO4/barium sulphate (1) IGNORE HSO4− If word and formula given, both must be correct

Inference Ni(OH)2 / nickel(II) hydroxide / Ni2+ / Nickel(II) compound (1)

ACCEPT words or formulae

Inference transition metal ion/compound OR any two from: Nickel/chromium(III)/copper/iron(II) vanadium(III) ion/compound (1)

81

NiSO4 / NiSO4.6H2O – NOT stand alone, there must be a logical progression from inferences

insoluble in acid/HCl OR no change in acid/HCl (1)

Observation any green (solution) (1)

(a)

8080/9080 Chemistry Summer 2006

1.

Unit 6246/01C Practical Test Group 3

(1 mark)

(3 marks)

(3 marks)

(2 marks)

8080/9080 Chemistry Summer 2006

(h)

(g)

Observations Yellow / any brown solution (1) IGNORE precipitate

(f)

KI

Lilac/mauve (1) ALLOW purple

Observation

Blue / black / blue-black (1)

Observations Any yellow precipitate (1) NOT “cream” on its own NOT “white” on its own

(e)

Inferences

-

Inference

OR

Inferences

82

K /potassium ion /potassium / K (1)

+

2I → I2 + 2e (2)

-

I- oxidised (1) to Iodine / I2 (1)

OR ”iodide”/I-/AgI or bromide /Br- /AgBr – BUT must follow correct “mixed” observation.

Iodide / I- / AgI (1)

(Total 18 marks)

(1 mark)

(2 marks)

(4 marks)

(2 marks)

(d)

Fruity/sweet/glue smell /any nail varnish (1) NOT pungent

Observation

58 (1)

m/e value of molecular ion

Observation Any red precipitate (1)

(b)

(c)

Observation Yellow/orange precipitate (1)

(a)

8080/9080 Chemistry Summer 2006

2.

83

O

H

C2H5C

O

H

Ester (1) (S is an) alcohol (1)

Inferences

(1) IGNORE any +ve charge, BUT a −ve charge (0) ALL Hs must be shown If ketone inferences in (b) credit propanone structure

CH3CH2C

Structural formula

If no red ppt/no change as observation, ALLOW inferences ketone/“not aldehyde”

Inference Aldehyde / CHO / “not ketone” (1)

Inference Carbonyl / C=O / both “aldehyde and ketone” (1)

(3 marks)

(2 marks)

(2 marks)

(2 marks)

8080/9080 Chemistry Summer 2006

(f)

(e)

(iii)

(ii)

(i)

CH3CH(OH) / 20 methyl alcohol and ethanol (1)

Triiodomethane/ iodoform/CHI3 (1)

Inferences

0.9

CH2

3.6

OH

5

(1)

84

ACCEPT acidified potassium dichromate(VI)/dichromate(VI) ions (1) orange to green (1)

Phosphorus pentachloride (1) allow formula Steamy / white / misty / fumes or gas / turns damp litmus red / gas which gives white smoke with ammonia (1) NOT white smoke

Butan-2-ol would have 5 peaks / no peak at CH shift value (1)

CH3

OR

3 peaks so 3 types of hydrogen atoms / protons(1) Peak “1” due to H in OH, peak “2” due to Hs in CH2, peak “3” due to Hs in CH3/ 5 peaks would be butan-2-ol (1)

H H

H C C O H

H H

Yellow precipitate (1)

Observation

(Total 17 marks)

(2 marks)

(2 marks)

(1 mark)

(3 marks)

(c)

(b)

(a)

8080/9080 Chemistry Summer 2006

3.

IGNORE “impurities” IGNORE “hard to judge bubbles” IGNORE “hard to read thermometer” IGNORE “distillation”

85

“Not enough temperature control”/heating too rapid

Inaccurate thermometer

Temp of liquid may not be same as temp of water

Place thermometer directly in X /cool down more slowly Replace by more accurate thermometer / digital thermometer Repeat to obtain a second pair of readings

Consequential improvement (1)

Boiling temperatures are too close together

(ii) Reason (1)

Identifying X as the ester with Table 2 boiling temperature closest to mean of candidate’s recorded temperatures. [Mean of candidate’s rising and falling temperatures, calculated by examiner, and recorded to 1 dp next to Table 2]

(i)

Comparison with Supervisor’s mean temperature then ± 1 oC (2) ± 2 oC (1) Write mean used for comparison on script “S = …..” near Table 2

For both temperatures within 2 oC of each other (2) within 3 oC (1) IGNORE decimal points here [Put the ticks above Table 1]

E is ethyl ethanoate: boiling point 77 oC

(Total 8 marks)

(2 marks)

(1 mark)

(1 mark)

(4 marks)

9

7

9

6

9

5

9

4

9

3

9

2

9

1

Effervescence with H2SO4 (1)

White precipitate with MgSO4 (1)

Add Na2CO3 to remaining two solutions (1)

Effervescence with Na2CO3 / BaCO3∴Na2CO3 identified (1)

86

Add HCl to each of remaining three solutions / add HCl to three white precipitates (1)

No change / no ppt with HCl (1)

(Total 7 marks) Total for Paper: 50 marks

White precipitates with Na2CO3, H2SO4, MgSO4 allow “white ppts with three solutions” if HCl clearly also identified(1)

Add aqueous barium chloride to each solution

8080/9080 Chemistry Summer 2006

4.

Materials Each candidate will require: (a) 1.0 g of hydrated nickel(II) sulphate, NiSO4.6H2O, in a stoppered specimen tube labelled P. The identity of this compound is not to be disclosed to candidates; (b) 1.0 g of potassium iodide, KI, in a stoppered specimen tube labelled Q. The identity of this compound is not to be disclosed to candidates; (c) 3 cm3 of propanal in a stoppered test tube labelled R. The identity of this compound is not to be disclosed to candidates; (d) 3 cm3 of ethanol in a stoppered test tube labelled S. The identity of this compound is not to be disclosed to candidates; (e) 1 cm3 of ethanoic acid in a stoppered test tube labelled ethanoic acid; (f) 1 cm3 of ethyl ethanoate in a stoppered ignition tube labelled X. The identity of this compound is not to be disclosed to candidates; (g) 10 cm3 of aqueous sodium hydroxide; concentration approximately 0.5 mol dm–3; (h) 2 cm3 of aqueous nitric acid; concentration approximately 2.0 mol dm–3; (i) 5 cm3 of aqueous hydrochloric acid; concentration approximately 2.0 mol dm–3; (j) 5 cm3 of aqueous barium chloride; concentration approximately 0.2 mol dm–3; (k) 2 cm3 of aqueous silver nitrate; concentration approximately 0.05 mol dm–3; (l) 5 cm3 of 2,4-dinitrophenylhydrazine solution. This may be prepared by adding 0.1 g of the solid reagent to a mixture of 45 cm3 of water and 5 cm3 of concentrated hydrochloric acid, stirring and filtering if necessary. Alternatively, centres may prepare this reagent using their own procedure providing the reagent gives a positive result with propanal; (m) 3 cm3 of approximately 10 vol aqueous hydrogen peroxide; (n) 3 cm3 of Fehling’s solution A and 3 cm3 of Fehling’s solution B. The solutions may be purchased or made up by the centre. The solutions should give a positive result with propanal; (o) access to a bottle of concentrated sulphuric acid; (p) 60 cm3 of approximately 1.0 mol dm–3 aqueous sodium carbonate;

8080/9080 Chemistry Summer 2006

87

8080/9080 Chemistry Summer 2006

88

Unit 6246/02 Section A 1

(a)

(i)

(ii) (b)

pink to colourless NOT clear OR pink is decolourised ALLOW pale red instead of pink NOT “pink goes” on its own NOT purple NOT Red NOT any of these in combination with pink NOT Magenta NOT Cerise

(1 mark)

8 – less than 11 - Any number or range within this range

(1 mark)

IGNORE SF in (b) (i)

initial no. moles NaOH = 1.00 x 25.0 = 0.0250 (1) 1000 no. moles HCl used = 0.100 x 8.80 = 8.80x10-4 (1) 1000 no. moles Na OH left in 25 cm3 = 8.80x10-4 OR indication of 1:1 ratio (1) no. moles NaOH left in 250 cm3 = 8.80x10-3 (1) no. moles NaOH used = 0.0250 – 8.80x10-3 = 0.0162 (1) 0.0162 with some working involving titre (5) Units not required BUT incorrect units eg mol dm-3 loses the 5th mark

(ii)

(5 marks)

no. moles hydrolysed = (b)(i) (1) = 8.1 x 10-3 2 EITHER mass of aspirin 8.1 x 10-3 x 180 = 1.458 g (1) % aspirin = 1.458 x 100 = 97.2 % (1) 1.50 OR Theoretical moles aspirin = 1.5 = 8.33 x 10-3 (1) 180 % aspirin = 8.1 x 10-3 x 100 = 97.2 % (1) 8.33 x 10-3 ALTERNATIVE METHOD Theoretical moles aspirin = 1.5 = 8.33 x 10-3 (1) Theoretical moles NaOH = 2 x 8.33 x 10-3 (1) = 0.01667 % aspirin = (b)(i) x 100 = 97.2 % (1) 0.01667 Mark consequentially but do not allow > 100 % (3 marks)

8080/9080 Chemistry Summer 2006

89

(c)

(2 marks) Total for question:12 marks

8080/9080 Chemistry Summer 2006

90

Section B 2

(a)

Molecular formula of D C5H10O2 (2) with some correct working / deduction eg C 58.8 x 102 = 5 100 12 H 9.8 x 102 = 10 100 1 O 31.4 x 102 = 2 100 16 OR Use % to find empirical formula (1) then use or refer to molar mass to deduce molecular formula (1) E Is propan-2-ol (1) ACCEPT name or formula IF name and formula given, both must be correct Must contain CH3CH(OH)/be a secondary 2-ol/methyl secondary alcohol, as it gives iodoform ppt. (1) Do not allow if methyl ketone included G Is Iodoform/CHI3 (1) – stand alone mark IF name and formula given, both must be correct F Is the sodium salt of the acid/sodium ethanoate (produced by hydrolysis of the ester) (1) (so is sodium ethanoate) with justification for number of carbon atoms eg must contain 5-3=2 carbon atoms (1) ACCEPT name or formula ALLOW 1 max (out of 2) if “ethanoic acid + reasoning for number of C atoms”

8080/9080 Chemistry Summer 2006

91

D is H O

H

H C C O C CH3 H

CH3

1-methylethylethanoate CH3COOCH(CH3)2

CH3CO2CH(CH3)2 (1)

ALLOW 2-propylethanoate

D is consequential on their unambiguous E + F NOT just “propylethanoate” unless correct formula given Equation CH3COOCH(CH3)2 + NaOH → CH3COONa + (CH3)2CHOH (1) NOT molecular formula for D Consequential on their D ALLOW CH3COOC3H7 for D and C3H7OH for E Candidates can identify D, E and F in the equation

8080/9080 Chemistry Summer 2006

92

(9 marks)

(b)

ALLOW correct names or formulae for reagents. If both given, both must be correct Condition mark only scores if correct or nearly correct reagents Step 1 CH3Cl / CH3COCl / any halogenoalkane/ any acylchloride (1) + (anhydrous) AlCl3 / Al2Cl6 / FeCl3 / Fe2Cl6 (1) ALLOW other halides except FeI3 If “RCl” plus correct condition ALLOW condition mark Intermediate methylbenzene/C6H5CH3 or other derived from their Freidel Crafts reagent (1) If step 1 uses “HCOCl” 4 max with -1 for each error. Step 2 KMnO4 /potassium manganate(VII)/ MnO4− (1) ALLOW “potassium manganate, KMnO4” NaOH/alkaline/OH−(aq) and heat/reflux (1) NOT warm ACCEPT specified temperature provided it is ≥ 100 °C Step 3 Acid/acidify / H+(aq)/named mineral acid (1) ALTERNATIVE Step 1 Br2 OR any halogen (1) FeBr3 etc (1) Intermediate bromobenzene (1) Step 2 Mg and dry ether (1) Step 3 (Solid) CO2 (1) Step 4 Acid/water (1)

(6 marks)

ALLOW any correct synthesis with –1 for each error or omission made. If synthesis does not work, mark as follows: Start at beginning and mark until incorrect. Then start at end and mark until incorrect. Then award whichever “route” through gives the highest mark.

8080/9080 Chemistry Summer 2006

93

(c)

HNO3 + H2SO4 → H2O + HSO4− + NO2+ - Can be shown in two stages OR HNO3 + 2H2SO4 → H3O+ + 2HSO4− + NO2+ (1)

1st curved arrow from benzene ring of electrons towards N of NO2+ ion (1) ALLOW the “+” anywhere on NO2 Intermediate correctly drawn, including positive charge (1) Curved arrow from C-H bond back into benzene ring (1) IGNORE if towards the “+” ALLOW HSO4− but arrow must start on O ALLOW arrow from negative charge ALTERNATIVE

1st curved arrow from double bond towards N of NO2+ ion (1) ALLOW the “+” anywhere on NO2 Intermediate correctly drawn, including positive charge (1) Curved arrow from C-H bond back into benzene ring (1) IGNORE if towards the “+”

(4 marks)

Total for question 19 marks

8080/9080 Chemistry Summer 2006

94

3

(a) QWC*

Temperature 975 – 1225 K OR 700-950 oC (1) ALLOW any number or range within these values (Forward) reaction is exothermic so the highest yield should be at low temperature (1) OR reverse argument Rate is too slow at low temperature, so compromise (1) NOT just “a compromise”, it must be related to rate Catalyst Platinum (and rhodium) to give a fast rate at lower T OR Pt etc…. speeds up conversion to NO and not combustion to N2 (1) ALLOW Pt etc increases rate / lowers Ea Pressure 2-10 atmospheres / 200 – 1000 kPa (1) – stand alone ALLOW any number or range within these values (Small) increase/very little difference in number of (gas) molecules/moles on r.h.s. so low pressure (1) - stand alone OR 2-10 atmospheres / 200 – 1000 kPa (1) ALLOW any number or range within these values To push gases through (1) – provided quoted or implied pressure

(b)

(i)

C4H4O62− + 5H2O2 + 2H+ → 4CO2 + 8H2O 1:5 ratio and no electrons in equation (1) Rest correct ie H+ and H2O cancel (1)

(6 marks)

(2 marks)

(ii) Rapid/fast effervescence (∴ rate has increased) (1) Colour change to green and back to pink/original colour (∴ alternative route/ not used up) (1) Do NOT allow if stated “it does not take part in reaction” NOT just “back to pink” NOT just “pink colour returns” They can change oxidation state easily/have variable oxidation states/can be illustrated (1)

8080/9080 Chemistry Summer 2006

95

(3 marks)

(iii) QWC*

axes both labelled correctly (1) eg percentage/fraction/number of molecules (with energy E) for y-axis eg energy/kinetic energy for x-axis NOT speed shape of graph (1) starts at the origin (and rises steeply) peak skewed to left asymptote (if line crosses the x axis do not award this mark) All 3 needed Do not award the mark if two or more curves are drawn for different temperatures.

Both activation energies shown well to the right of the peak (1) Comment on relationship of area under curve to number of particles with E≥Ea eg more of molecules/collisions have energy greater than or equal to the activation energy/have enough energy to result in a reaction (1) Therefore a higher frequency of collisions result in reaction OR more (of the) collisions result in reaction OR more successful collisions per unit time OR more of the collisions are successful OR greater proportion of the collisions are successful (1)– stand alone NOT just “ more successful collisions”

8080/9080 Chemistry Summer 2006

96

(5 marks)

(c) no. moles O2 = 100 24000 = 4.17 x 10-3

OR 24000 cm3 O2 from 2 mol H2O2 (1)

(1)

no. moles H2O2 = 2 x 4.17x10 = 8.33x10-3

-3

(1)

therefore 100 cm3 from 2 x 100 24000 = 8.33 x 10-3 mol (1)

Mark consequentially on moles of O2 volume H2O2 = 8.33x10-3 x 1000 0.5 16.7 cm3 (1)

8.33 x10-3 0.5 = 0.0167 dm3 (1)

Answer and unit required for third mark IGNORE s.f. Mark consequentially on moles of H2O2

(3 marks) Total for question: 19 marks

8080/9080 Chemistry Summer 2006

97

4

(a)

(i)

Fe2O3 + 3CO → 2Fe + 3CO2 (1)

∆H = (3 x –394) - (3 x –110) – (-822) = -30 (kJ mol-1) (2) Multiply by 3 twice (1) Correct answer with sign (1) ALLOW consequential calculation if wrong stoichiometry If O2 given as product 1 max on consequential calculation (ii)

(3 marks)

(i) is more likely because the rate of a reaction between a solid and a gas will be faster than that between two solids ALLOW (i) is more likely because it is exothermic (and (ii) is endothermic) OR products in (i) are more thermodynamically stable relative to reactants than in (ii) (1 mark)

Consequential on (a)(i) (b)

(i)

Kp = pH24 pH2O4

(1) “p’s” are essential NO [ ]

= 1.64 = 3.16 / 3.2 and no units (1) 1.24 Consequential on Kp expression provided no Fe or Fe3O4 included (ii) Q W C*

KP decreases (1) Because forward reaction release heat / exothermic OR reverse reaction absorbs heat / endothermic (1) Dependent on Kp decreases Do not allow 2ND mark if decrease is explained in terms of position moving to the left, UNLESS moving is a consequence of Kp decreasing.

(c)

(2 marks)

IGNORE state symbols X: 2H2O + O2 + 4e(−) → 4OH− (1)

OR ½ this OR multiples (1)

Y: Fe → Fe2+ + 2e(−) / Fe − 2e(−) → Fe2+ IF X and Y not identified 1 (out of 2) iron(II) hydroxide (1) ALLOW Fe(OH)2 / [Fe(OH)2(H2O)4]

8080/9080 Chemistry Summer 2006

(2 marks)

(1)

(3 marks)

98

(d)

covalent bonds labelled (1) dative bonds labelled OR shown as arrows (1) ALLOW dot and cross diagram (2) Structure with Fe-Fe bond does not score first two marks Tetrahedral (around Fe) (1) ALLOW good 3-D diagram dependent on 4 covalent/dative bonds around Fe If Al2Cl6 ALLOW max 2 (out of 3) Any mention of ionic 0 (out of 3)

(e)

(i)

(3 marks)

add (aqueous) sodium hydroxide / ammonia (1) ALLOW OH−(aq) red/brown/foxy red/red-brown/rust ppt/solid (1) OR add (aqueous) potassium hexacyanoferrate(II)/hexacyanoferrate(II) ions (1) (Prussian) blue ppt/solid (1) – ALLOW result for near miss spelling of reagent OR add (aqueous) potassium thiocyanate (1) blood red (solution) (1) NOT ppt

(ii)

(2 marks)

Fe3+ polarises the (OH bond in water) ligands (1) [Fe(H2O)6]3+ + H2O → [Fe(OH)(H2O)5]2+ + H3O+ OR in words eg deprotonation (of the ligand) by the (solvent) water (1) the H3O+ / H+(aq) ions make the solution acidic (1) – stand alone

(3 marks)

Total for question: 19 marks Total for paper: 50 marks

8080/9080 Chemistry Summer 2006

99

Further copies of this publication are available from Edexcel Publications, Adamsway, Mansfield, Notts, NG18 4FN Telephone 01623 467467 Fax 01623 450481 Email [email protected] Order Code UA 017774 Summer 2006 For more information on Edexcel qualifications, please visit www.edexcel.org.uk/qualifications Alternatively, you can contact Customer Services at www.edexcel.org.uk/ask or on 0870 240 9800 Edexcel Limited. Registered in England and Wales no.4496750 Registered Office: One90 High Holborn, London, WC1V 7BH