Chem Ark Scheme Jun 07 As

Mark Scheme (FINAL) Summer 2007

GCE

GCE Chemistry (6241/01)

Edexcel Limited. Registered in England and Wales No. 4496750 Registered Office: One90 High Holborn, London WC1V 7BH

General Guidance on Marking Examiners should look for qualities to reward rather than faults to penalise. This does NOT mean giving credit for incorrect or inadequate answers, but it does mean allowing candidates to be rewarded for answers showing correct application of principles and knowledge. Examiners should therefore read carefully and consider every response: even if it is not what is expected it may be worthy of credit. Crossed out work should be marked UNLESS the candidate has replaced it with an alternative response. 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 2 3 4 5

/ means that the responses are alternatives and either answer should receive full credit. ( ) 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. [ ] words inside square brackets are instructions or guidance for examiners. Phrases/words in bold indicate that the meaning of the phrase or the actual word is essential to the answer. 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.

EXPECTED ANSWER 1.

(a)

(b)

79 35

ACCEPT

REJECT

MARK

Br : 44 neutrons (1)

81 35 Br

: 35 protons(1)

81 35 Br

: 36 electrons(1)

Na 2s2 2p6 3s1 (1) Br 2s2 2p6 3s2 3p6 3d10 4s2 4p5 (1) Ignore repeat of 1s2

(c)

They have the same (number of protons and) electron(ic) configuration Same (number of protons and)electronic structure Same (number of protons and)electron arrangement same (number of protons and)number of electrons MUST MENTION ELECTRONS

(d)

Mass spectrometer

(e)

(78.93 x 50.54) + (80.91 x 49.46) (1) 100 = 79.91(1) 2nd mark consequential on transcription error data used Correct answer with no working scores 2 Answer to 4 S.F. with NO units but allow g/mol-1

3

Allow subscripts and ignore capital letters Allow 4s2 3d10 4p5 Allow p as pxpypz with 2 in each

Allow variations of spelling

2

‘Just‘ Same number of protons ‘Just’ same number of electron shells same number of outer electrons same number of electrons in outer shell Correct answer followed by reference to outer shell scores (0) Mass spec

1

1

2

(f)

EXPECTED ANSWER Between the atoms: Covalent(1)

ACCEPT

Between the molecules :Induced dipole-(induced) dipole OR dispersion OR London OR van der Waals OR instantaneous OR Temp dipole - (1) (forces)

Variations on van der Waals such as de and walls, vdW

(g)

Brown OR orange OR red

Any combination of these colours

(h)

Yellow OR Orange OR any combination IGNORE words such as ‘bright’ or ‘persistent’ or ‘lasting’ or ‘golden’ or ‘intense’

(i)

(j)

2Na + Br2→ 2NaBr 1 mark for balanced equations IGNORE state symbols Metallic

(k)

Ionic

/ electrovalent(1) .. .. .. [Na]+ [ :Br:]- OR [:Na:]+ [:Br:].. .. .. 1 mark for correct charges 1 mark for electrons Penalise wrong symbol only once Allow dots or crosses If choose to give inner shell electrons they must be correct

REJECT

MARK 2

Dipole-dipole OR ‘JUST’ intermolecular forces ID-ID 1

1

½ or multiple 2Na+Br- For 2NaBr

Charge could be on central atom e.g. Na+ [ ] not necessary If charges omitted can score electrons mark provided not covalent i.e. sig gap between Na & Br Arrow to show transfer of an electron on its own does not score as this does not answer the question

Na+ + Br-

1

Metal

1

Anything that looks covalent scores zero.

3 Question total 18 marks

2

(a)

(i)

(ii)

(b)

(i)

(ii)

EXPECTED ANSWER 4LiNO3 →2Li2O + 4NO2 + O2 Species (1) Balance(1) Not stand alone conditional on correct species 2CsNO3 → 2CsNO2 + O2 Correct balanced equation

ACCEPT Or fractions/ multiples

There must be a comment about both barium and calcium to score both marks Barium would react to produce a (colourless)/(clear) solution does not give a ppt./ clear (1)

Allow Ba and Ca in argument Barium hydroxide dissolves

Calcium would go cloudy /give (white) ppt.(1) E.g. Calcium would go cloudy but barium (goes) clear (2) Insoluble/ solid/layer / coating of barium sulphate formed (1) allow equn with BaSO4(s) Must say what the coating is since question says use information in table Which prevents acid getting to surface (of barium) (1) 2nd mark conditional on 1st need some idea that a substance is formed that generates a barrier to further reaction

REJECT

Or fractions/ multiples

If candidate uses word ppt must be clear that this is on the surface of the barium or causes interference

MARK 2

1

Goes colourless

2

Other colours BaSO4 unreactive Barium disappears Any reference that implies barium all used up or was a very small piece or acid not in excess or reaction over scores zero References to other layers such as oxide/hydroxide

2

(c)

Insoluble

1

(d)

Ca(s) + 2H+(aq) → Ca2+(aq) + H2(g) 1 mark for equation 1 mark for state symbols

2 state symbol mark for correct molecular equation Ca(s)+2HCl(aq) →CaCl(aq) +H2 (g) Scores (1) Question total 10 marks

3

(a)

(i)

(ii)

(b)

(i)

EXPECTED ANSWER Enthalpy/heat/ energy required/change to remove 1 electron(1) from each of one mole(1) of gaseous atoms (of an element)(1) Ignore references to gaseous electrons O+(g) → O2+(g) + e(-) Or O+(g) - e(-) → O2+(g) State symbols required

ACCEPT X(g) → X (g) + e 2 marks for the change and the state but not the mol Isolated atoms in place of gaseous

There is a large increase after the removal of 6 electrons(1)

Large increase before removal of 7th electron (Big) jump between 6 and 7

+

REJECT If incorrect equation given after correct def -1 mark

MARK

3 E ( for element) in place of O

1

2

(Group) 6 (1) Stand alone

(ii) (c)

(Need to look at diagram for annotation) Sulphur / S / S8 (1) Not CQ

S8+ 1 mark ‘S8’ 1 mark ‘+’ Stan alone

1 32

S8

+

2

Question total 9 marks

4

(a)

(i)

EXPECTED ANSWER Answer must identify ions as sodium ions / Na+ and chloride / ClAnswer must describe structure. Ignore any references to the bonding. Examples 6 sodium ions / Na+ around each chloride ion (1) and 6 chloride ions /Cl- around each sodium ion (1) OR Cubic structure(1) With alternating sodium and chloride ions (1)

ACCEPT A correctly labelled diagram to support text for both marks A diagram showing just Na+ & Cl- can score 1 mark

REJECT Any mention of atoms loses the mark that relates to ions Any reference to covalency loses the mark that relates to ions

Reference to oppositely charged ions without saying what they are scores max 1

Chlorine ions

If diagram drawn ignore relative sizes

Closely packed does not mean cubic

OR Two interlocking cubic lattices(1) of sodium and chloride ions(1) OR Cube (1) With alternating sodium and chloride ions(1)

MARK

2

OR Cubic lattice (1) With alternating sodium and chloride ions(1) OR 6:6 co-ordinate lattice(1) of sodium and chloride ions(1)

(ii)

Layers/Planes/Sheets (1) (interlocking) hexagons of carbon atoms (in which each carbon bonded to three other carbon atoms) (1) nb Hexagonal layers of carbon atoms (2)

Correct labelled diagram to support text for both marks Discussion based on electrons being sp2 hybridised

Max 1 mark if bonding between layers wrongly identified Ref to any number other than 3 scores max

2

(b)

EXPECTED ANSWER Weak /induced dipole-(induced) dipole/ dispersion/ London/ van der Waals forces between layers(1)

ACCEPT

REJECT Wrong intermolecular forces e.g. Hydrogen bond

MARK 2

Allows layers to slide over each other /layers break off(on to the paper) (1) Stand alone mark (c)

(i)

(in molten sodium chloride, (Na+ and Cl- )) ions can move (to carry current)

(ii)

electrons can move (1)

Not just ions move Not NaCl ions Free electrons Mobile electrons Sea of electrons Delocalised ions/electrons

1

1 Question total 8 marks

5

(a)

(b)

EXPECTED ANSWER Any statement that means the number gets less Eg Decrease (in oxidation number of an element) Reduction of ON Lowering of ON ON becomes more negative ON becomes less positive (i) 2NaBr + 3H2SO4 → 2 NaHSO4 + SO2 + Br2 + 2H2O OR 2NaBr + 3H2SO4 → 2 NaHSO4 + …SO2 + … Br2 + 2H2O OR 2NaBr + 3H2SO4 → 2 NaHSO4 + 1SO2 + 1Br2 + 2H2O (ii)

H2SO4 : +6 / 6 / VI / 6+ HSO4-: +6 / 6/ VI / 6+ SO2 : +4/4/IV / 4+ H2S : -2 / -II / 2All four correct 2 marks Any 3 correct 1 mark

(iii)

Change in ON of S increases down (halide) group (1) Link all three changes to actual numbers with halide (1) Consequential on answers to part(ii)

ACCEPT

REJECT ‘Just’ Gain of electrons

MARK 1

1

Correct answer referring to only two halides scores 1 mark

Superscript + e.g S6+

2

If ref to halogens lose second mark

2

Question total 6 marks

6

(a)

EXPECTED ANSWER The number of atoms in 12g of 12C (2) The number of atoms in 1 mole of 12C (2)

(b)

(i)

1.907 g of Z contains 2.87 x 1022 1.907 x 6.02 x 1023/ 2.87 x 1022 is 1 mol(1) = 40.(0) (1) No units but allow 40 g/mol IGNORE s.f. in answer

(ii)

Allow 39.7 for 2 marks this is rounding 0.04767 to 2 sig figs in calc Allow 38.14 for 1 mark as this is rounding to I sig fig. Correct answer with some working (2) Ar / Argon Consequential on (i) but must be nearest group 0

ACCEPT Number of atoms in 1 mole (1) of atoms / stated monatomic substance (1) OR Number of molecules in 1 mole (1) of molecules / stated molecular substance (1) OR Number of electrons in 1 mole (1) of electrons (1) OR Number of particles in 1 mole (1) max

REJECT If answer just quotes the number it does not score it is in the question. Number of particles in 1 mole of a substance

MARK 2

Moles of Z = 2.87 x 1022 / 6.02 x 1023 = (0.04767) (1) Atomic mass = 1.907/moles = 40.(0) (1)

2

1

EXPECTED ANSWER (c)

(i)

Amount hydrogen peroxide produced = 3.09 = 0.09088 (moles) 34 (1) Amount of potassium superoxide = 0.09088 x2 (moles) (1)

ACCEPT 34g of H2O2 requires 2 x 71g of KO2 (1) 3.09g requires

REJECT

MARK 3

2 × 71 × 3.09 34

(1) or (2) if this is start line =12.9g (1) mass of potassium superoxide = 0.09088 x2 x 71 = 12.9g (1) / 13g incl unit but ignore S.F. (note = 6.45 g scores 2 marks)

If round 0.09088 to 0.09 can score 2 marks for 12.78

Correct answer with some working scores 3 marks (ii)

Volume of oxygen = 3.09 x 24 = 2.18 dm3 (1) IGNORE s.f. & do

2.2

1

34

not penalise lack of units twice Allow error carried forward. i.e if omit to x2 in part (i) only penalise it in part (i) not here Question total 9 marks

Mark Scheme (FINAL) Summer 2007 GCE

GCE Chemistry (6242/01)

Edexcel Limited. Registered in England and Wales No. 4496750 Registered Office: One90 High Holborn, London WC1V 7BH

General Guidance on Marking Examiners should look for qualities to reward rather than faults to penalise. This does NOT mean giving credit for incorrect or inadequate answers, but it does mean allowing candidates to be rewarded for answers showing correct application of principles and knowledge. Examiners should therefore read carefully and consider every response: even if it is not what is expected it may be worthy of credit. Crossed out work should be marked UNLESS the candidate has replaced it with an alternative response. 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 2 3 4 5

/ means that the responses are alternatives and either answer should receive full credit. ( ) 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. [ ] words inside square brackets are instructions or guidance for examiners. Phrases/words in bold indicate that the meaning of the phrase or the actual word is essential to the answer. 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.

Quality of Written Communication Questions which involve the writing of continuous prose will expect candidates to: • show clarity of expression • construct and present coherent arguments • demonstrate an effective use of grammar, punctuation and spelling. Full marks will be awarded if the candidate has demonstrated the above abilities. Questions where QWC is likely to be particularly important are indicated (QWC*) in the mark scheme BUT this does not preclude others.

EXPECTED ANSWER 1.

(a)

titanium OR Ti

(b)

2ClOR Cl-

→

Cl2 + 2e-

→

½ Cl2 + e-

ACCEPT graphite /C

REJECT

2Cl- - 2e- → Cl2 OR Cl- - e- → ½ Cl2

MARK (1)

(1)

there does not have to be a negative charge on the e IGNORE state symbols (c)

(d)

(e)

oxidation because chloride (ions)/Cl-/chlorine ions lose electrons OR oxidation because chloride (ions)/Cl-/chlorine ions lose 2 electrons OR oxidation because chloride (ions)/Cl-/chlorine ions lose 1 electron OR oxidation because ox no. chlorine/Cl goes up( by 1) OR oxidation because ox. no chlorine/Cl goes from -1 to 0 Cations

Na+ / sodium (ions)

OR positive (ions)

OR H+/hydrogen (ions)

Hydrogen / H2

H2 + 2OHOR H2+ OH-

OR sodium hydroxide / NaOH / hydroxide ions/OH— OR both of these

chlorine/Cl/Cl2/it loses electrons

(1)

just ‘loss of electrons’

(1)

H 2H+ + 2e- → H2

(1)

(f)

EXPECTED ANSWER 2NaOH + Cl2 + H2

2NaCl + 2H2O → OR NaCl + H2O → NaOH + ½Cl2 + ½ H2

ACCEPT 2Cl + 2H2O → 2OH- + Cl2 + H2

REJECT

MARK (2)

water purification OR swimming pools OR cleaning anything OR anything else

(1)

-

Or half the above equation

all species correct (1)

(g)

balancing (1) only if all species correct treatment of (drinking) water OR to kill bacteria in water/swimming pools OR sterilisation of water OR as a disinfectant OR in production/manufacture/making of any one of: PVC bleaches herbicides insecticides/pesticides HCl/hydrochloric acid/hydrogen chloride named solvents bromine titanium paper chloroethene poly(chloroethene)

as a bleach OR in bleach

Total 8 marks

EXPECTED ANSWER 2

(a)

ACCEPT

(i)

REJECT “Fl” for fluorine

MARK (1)

(ii)

C-F bond is stronger/ they are stronger/the bonds are stronger OR C-F higher bond energy/ enthalpy OR they have a higher bond energy/enthalpy

UV (photon) too low energy to break C-F bond

C-F or C-Cl as an ionic bond OR C-Cl bond is weaker OR any reference to difference in polarity or difference in electronegativity OR references to hydrogen bonding/van der Waals forces

(1)

(iii)

EXPECTED ANSWER neutral particles with an unpaired electron OR neutral species with an unpaired electron OR atoms/molecules with an unpaired electron (1)

(i)

Cl H

F

C C

C C

H H

F (1)

F F (1)

brackets are not required If extension bonds are missing from both, give total 1 mark if all other atoms and bonds are correct

REJECT ions/elements/substances with…….

MARK (2)

“unbonded electron/ free electron/ lone electron/ single electron” instead of “unpaired electron” Higher frequency than visible light

uv radiation (1) stand alone OR uv light OR sunlight (b)

ACCEPT

more than one repeat unit may be drawn but one repeat unit must then be clearly labelled or indicated by brackets, but only penalise this once

homolytic fission OR description of atoms taking electron from covalent bond OR just “high frequency light” -C=COR “Fl” for fluorine

(2)

(ii)

EXPECTED ANSWER PVC (1) electrical insulation pipes gutters/drainpipes window frames / door frames flooring waterproof clothing/waterproof footwear artificial leather (for clothing, handbags etc) rigid drink bottles toys fixtures for interiors of aeroplanes car seats / dashboards fencing / railings / decking / gates roofing membrane cladding (for houses) / fascia boards wallcovering credit cards PTFE (1) burette taps non-stick coating on saucepans plumbers tape Goretex lining ski coating cable insulation catheter tubing sewing thread / fibres (for socks) / hosiery tubing and piping in the semiconductor industry wiper blades leashes and collars harnesses / belts bicycle lubricants as a fabric protector coating for machine parts weatherproofing outdoor signs

ACCEPT

REJECT packaging buckets bowls plastic bags clothing for either polymer

MARK (2)

Total 8 marks

3.

(a)

EXPECTED ANSWER Ignore missing hyphens or addition of commas in both names propan-2-ol (1) alcohol (1) ignore secondary / 2y / 2o

ACCEPT

2-propanol OR propane-2-ol

3-methylpentane (1) alkane (1) ignore branched (b)

MARK (4)

2-hydroxypropane primary OR tertiary OR OH 2-ethylbutane

(i)

Molecules where the double bond is not shown OR trans isomer OR CHCl=CHCl (1)

(ii)

REJECT

(2)

CH2=CCl2 (1)

1,2-dichloroethene OR structure (cis or trans) (1)

as it has different atoms/functional groups on both (π bonded) C OR restricted/limited rotation about C=C OR the π bond restricts rotation (1) 2nd mark conditional on the correct identification

“both” if both cis and trans of 1,2 isomer and no 1,1 isomer is drawn in (i) no rotation about C=C/ π bond

(2) No free rotation about C=C/ π bond

Just “each carbon has the same two groups”

Ignore “each carbon has the same two groups” in combination with any correct answer. (c)

(d)

(i)

electrophilic addition

(ii)

nucleophilic substitution

C5H10

(1) Nuclearphilic substitution

(1)

(1) Total 11 marks

4.

(a)

EXPECTED ANSWER Correct answer 73.1 g with some working (2)

ACCEPT 73.05 g / 73.06 g / 73 g

REJECT

MARK (2)

There are several ways of achieving this e.g. (molar mass) CH4 = 16 (g mol-1) OR (molar mass) CH4 = 12+4 (g mol-1) (1) 1000× 16 = 73.1 g (1) 219

OR 219 kJ is produced from 16 g of CH4 (1) 1000 kJ is produced from 1000 x 16 = 73.1 g (1) 219 OR Number of moles CH4 = 1000 = 4.57 (1) 219 The mass of CH4 = 4.57 x 16 = 73.1 g (1) 2nd mark is consequential on their molar mass Ignore sig figs in final answer BUT units essential

80 g max 1

EXPECTED ANSWER

ACCEPT

(b)

REJECT Activation energy hump shown as straight lines

or

CH4 + (2)Cl2

and

Reactants and products

C + (4)HCl at correct levels (1)

∆H correct / -219 (1)

double headed arrow

-∆H

activation energy hump (does not need to be labelled) (1) Explanation: Q W C

Reaction/it has a high activation energy (1) IGNORE reactants/methane and chlorine are kinetically stable in combination with high activation energy uv provides energy to break Cl-Cl bonds (1) OR Cl radicals are produced in the presence of uv IGNORE any references to thermodynamic stability

UV provides the reactants with energy to overcome the Ea

MARK (5)

(c)

(i) Q W C

(ii) Q W C

EXPECTED ANSWER Stand alone marks

ACCEPT

REJECT

MARK

(2)

Lower yield / less hydrogen produced (1) IGNORE any reference to rate More (gaseous) molecules on rhs / fewer (gaseous) molecules on lhs (1)

Equilibrium move left / reverse reaction favoured, if no reference to yield

Higher yield / more hydrogen produced (1) - if this is only explained in general terms of increasing rate of the reaction, do not award the mark

If forward reaction is exothermic (0 out of 2)

(2)

(Forward) reaction is endothermic / absorbs heat (1) (iii)

No effect

(1) Total 12 marks

5.

(a) Q W C

EXPECTED ANSWER enthalpy / energy / heat change when 1 mol of a substance (1)

ACCEPT Heat / energy / enthalpy released Both “element and compound” instead of substance

REJECT Energy etc required “Reactant” instead of substance

is burnt in excess/burns completely in air/oxygen (1)

Complete combustion with air/oxygen OR Reacts completely with air/oxygen

Reacts with oxygen

conditions of 1 atm/ 100 kPa/101 kPa pressure and specified temperature/298 K (1) (b)

(i)

MARK (3)

Room temperature

Bottom box 2CO2(g) + 3H2O(l) balance and state symbols (1)

(3)

Left arrow label 2∆HcC + 3∆HcH2 OR (2x-394)+(3x-286) (kJ) units not essential OR -788-858 OR -1646 kJ (1) right arrow label ∆HcC2H5OH OR -1371 (kJ) (1) (ii)

∆HfC2H5OH = (2x-394) + (3x-286) –(-1371) (1) = -275 (kJ mol-1) (1) OR 1 mark for their left hand arrow minus their right hand arrow 1 for correct consequential sign and answer

(2) Wrong unit negates last mark (but allow kJ)

EXPECTED ANSWER (c)

Step 1 I2 / iodine (1) (moist red) phosphorus (1) IGNORE any solvent or heat Step 2 KCN /potassium cyanide OR NaCN / sodium cyanide (1)

ACCEPT

REJECT

PI3 (1)

Iodide PI5

CN—/ cyanide ions

cyanide / HCN

MARK (3)

IGNORE any solvent or heat Total 11 marks

6.

(a)

EXPECTED ANSWER → 4NO + 6H2O

(i)

4NH3 + 5O2

(ii)

Platinum OR Pt (1) IGNORE Rh OR rhodium

(iii)

(lowered rate because) particles / molecules have less (kinetic) energy (1)

Q W C

ACCEPT Multiples or half

REJECT

Rb OR rubidium in combination with Pt/platinum

fewer molecules have energy > Ea (1)

MARK (1) (1)

(3)

fewer (of the) collisions have energy > Ea fewer successful collisions per unit time

smaller proportion of collisions result in reaction/are successful OR fewer of the collisions result in reaction/are successful (1)

just “Fewer successful collisions”

IGNORE the effect on the yield “fruitful”/”effective” instead of successful (b)

cool NO/ the mixture (1)

(4)

(then) react with (excess) air / oxygen (1)

add/mix with (excess) air /oxygen

to form NO2/N2O4 OR nitrogen dioxide/dinitrogen tetroxide (1)

2NO+O2 Æ 2NO2/N2O4 (or half this) scores 2nd and 3rd marks

react with water OR 4NO2+ 2H2O+O2 Æ 4HNO3 OR 3NO2 + H2O → 2HNO3 + NO OR 3N2O4 + 2H2O → 4HNO3 + 2NO OR 2NO2+ H2O Æ HNO3 + HNO2 any equation on its own must be correct

(1)

dissolves/absorbed into/mixes with/ pass into water if there is an attempted equation to show a reaction with NO2/N2O4 + H2O on LHS and HNO3 on RHS

oxidised if air/oxygen not mentioned

EXPECTED ANSWER (c)

making any one of: fertilisers explosives nylon flares rocket propellants dyes ammonium nitrate

ACCEPT

REJECT any item from the ‘making’ list on its own OR in fertilisers etc

MARK (1)

OR in metal processing Total 10 marks

Mark Scheme (FINAL) Summer 2007 GCE

GCE Chemistry (6243/02)

Edexcel Limited. Registered in England and Wales No. 4496750 Registered Office: One90 High Holborn, London WC1V 7BH

General Guidance on Marking Examiners should look for qualities to reward rather than faults to penalise. This does NOT mean giving credit for incorrect or inadequate answers, but it does mean allowing candidates to be rewarded for answers showing correct application of principles and knowledge. Examiners should therefore read carefully and consider every response: even if it is not what is expected it may be worthy of credit. Crossed out work should be marked UNLESS the candidate has replaced it with an alternative response. 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 2

/ means that the responses are alternatives and either answer should receive full credit. ( ) 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. Quality of Written Communication Questions which involve the writing of continuous prose will expect candidates to: • show clarity of expression • construct and present coherent arguments • demonstrate an effective use of grammar, punctuation and spelling. Full marks will be awarded if the candidate has demonstrated the above abilities. Questions where QWC is likely to be particularly important are indicated (QWC) in the mark scheme BUT this does not preclude others.

1.

(a)

(b)

2

(a) Q W C

(b)

A

EXPECTED ANSWER ammonium sulphate / (NH4)2SO4 /

(NH4+)2SO42-

B

ammonia / NH3 (1)

C

barium sulphate / BaSO4 / Ba2+SO42- (1)

D

potassium bromide / KBr /K+Br- (1)

E

bromine / Br2 (1)

F

sulphur dioxide / sulphur(IV) oxide / SO2 (1)

ACCEPT Correct oxidation numbers e.g. barium (II) sulphate(VI)

(1)

3

Sequence must be chemically correct to score Add ≥ 50 cm3 (distilled) water (1)

Filter (mixture) (1)

Any volume ≥ 47.6 cm Ignore additional processes (e.g. evaporate to dryness) Mix, shake or warm (above room temp if a temperature is stated)

Wash residue (to remove excess solution) (1)

decant solution

Stir (to dissolve sodium carbonate) (1)

Re-crystallisation method scores max 3 orange instead of yellow Sodium gives yellow flame calcium gives (brick) red flame Use of ‘burning’ for flame test

Flame test (on residue) gives (brick) red colour (only) or gives no yellow colour

REJECT For each: -any incorrect name -any incorrect formula. -any incorrect ion or incomplete charges if given. -incorrect oxidation number For each: -any incorrect name -any incorrect formula. -any incorrect or incomplete ion charges if given. - incorrect oxidation number Sequence without water

Crimson, carmine

MARK (3)

(3)

(Total 6 marks) (4)

(1)

Total 5 marks

1

3

(a)

EXPECTED ANSWER Test: (excess) (dilute) nitric acid / HNO3 (1)

ACCEPT concentrated

Inference: chlorine / Cl (1) (b)

(c)

Observation: misty / steamy

MARK (2)

Cl- / chloride ion / Cl2 (1)

Inference:

hydrogen chloride / HCl (1)

Observation

stays orange / (1)

Inference

tertiary / 3o (1) stand alone

(d)

REJECT Any other reagent including any other acid.

White / cloudy

White smoke

(2)

Hydrochloric acid / acidic Does not turn (from orange to) green OR no change in colour

No reaction, OR no change OR no observation OR incorrect colour green remains green)

(2)

(e.g.

CH3 CH3CCl(CH3)CH3 CH3

C

CH3 (CH3)3CCl

Cl Must be tertiary; halogen consequential on inference in 3(a)

Formula with X or OH in place of halogen Correct name

(1)

Full structural formula showing all atoms separate. Total 7 marks

2

4

(a) Q W C

EXPECTED ANSWER IGNORE filling burette, use of pipette and other preliminaries even if there are errors.

ACCEPT

Add NaOH (quickly) to 20 - 23 cm3 (1)

Idea of NaOH addition fast intially then slow down near end point can score first mark

REJECT

MARK (4)

Slowly does not score drop by drop mark

Drop by drop (near end point) OR until one drop changes colour (1) stand alone

(b)

Swirl / rinse in drops solution in neck of flask (1)

Mix or shake or swill

Colourless to pink (1) both required

Colourless to red or Colourless (solution) starts to turn pink

Colourless to purple or magenta Clear to anything

(i)

Bottom of meniscus reasonably close to midway.

Inverted meniscus

Line with bottom of meniscus mid-way between 23.60 and 23.70. (1)

Straight horizontal line

Clear indication of correct volume (e.g. arrow to 23.65)

3

Non-horizontal lines

(1)

(ii)

EXPECTED ANSWER Ticks on titres 2 and 3 (1)

ACCEPT Ticks in 2 & 3 with cross in 1 Correct answer with no ticks (2)

23.55 (cm3) (1) not consequential

(c)

In (i) and (ii) penalise 1SF on the first occasion only. ACCEPT ≥ 2SF in (i) and (ii) (i) 25 x 0.0500 = 0.00125 (moles) 1000 (ii) Answer to (i) x 2 = 0.00250 (moles) (iii)

0.00250 x 1000 = 0.106 (mol dm-3) 3sf only 23.55 Consequential on b(ii) and c(ii)

REJECT Inclusion of titre 1 in calculation of mean scores zero

MARK (2)

Only one decimal place

0.001250 or 0.0013

(1)

0.0025; CQ on 2 i)

(1)

Correct answer (3 sf) no working

0.106 if 1000 omitted in (c)(i) and (iii) (0)

(1)

Total 10 marks

4

5

(a)

EXPECTED ANSWER In (a)(i), (ii) and (ii) penalise 1SF on the first occasion only. ACCEPT ≥ 2SF (i) Mass methanol burnt = 0.34 (g) (1)

ACCEPT

REJECT

MARK

(2)

0.34 = 0.0106 (1) 32

0.011, 0.01063, 0.010625 CQ on incorrect calculation of mass Correct answer with some working (2)

(ii)

Temperature rise = 43.5 – 22 (= 21.5) (o C) (1)

(2)

(Heat energy =) 21.5 x 4.18 x 50 = 4.49 (kJ) (1) 1000

CQ on incorrect calculation of temp. Correct answer with some working (2)

The temperature rise mark can be scored from the heat energy expression (iii)

Answer (ii) = 4.49 Answer (i) 0.0106

(1)

CQ on (i) and ii)

= ― 422.9 (kJmol―1) [calculator stored value] OR = − 423.6 (kJmol―1) [using rounded values] (1) minus sign and value both required

Answers in the range ―420 to ―424 Correct answer with some working (2)

If the final answer is incorrect the 2nd mark is only accessible if energy is divided by moles in first part of calculation

5

Answer in Joules

(2)

(b)

(i)

(ii)

EXPECTED ANSWER 1.0 x 100 = (±)4.65 % 21.5 IGNORE SF

ACCEPT

(21.5 + 1.0 =) 22.5 (oC) OR (44 – 21.5)=22.5 (oC) OR

REJECT

MARK (1)

All other values

(1)

Balance faulty or spills or Methanol reacts

(1)

104.5 ⎞ ⎛ ⎜ 21.5 x ⎟ = 22.5 (oC) 100 ⎠ ⎝ CQ on % error in b(i) if this is used to calculate the temperature (c)

(i)

Evaporation (of methanol/alcohol)

Turns to vapour OR methanol volatile

(ii)

Carbon (1)

Soot

Any other substance

(2)

Lower/less exothermic (1) ignore references to incomplete combustion Total 11 marks

6

6

(a)

(i)

EXPECTED ANSWER Apparatus I (heating under) reflux (1) Apparatus II

(b)

(expansion of vapour will) build up pressure

(i)

Reaction is vigorous OR exothermic OR (very) fast or violent (One or both of) the liquids flammable OR ethanol is flammable OR iodoethane is flammable OR ethanol and iodoethane are flammable

(iii)

To allow reaction to reach completion OR reaction is slow OR reaction has high activation energy.

(iv)

The lower range is 70 to 71 The upper range is 72 to 74 e.g. 70 to 74 oC OR 71 to 73 oC OR 70 to 73 oC

REJECT

MARK (2)

Fractional distillation

distillation (1)

(ii)

(ii)

ACCEPT

Prevent explosion

To maximise yield

Dangerous OR to prevent vapour escaping

(1)

Dangerous

(1)

Substances or Reactants are flammable

(1)

(1)

(1)

7

(c)

EXPECTED ANSWER In (i), (ii) and (ii) penalise 1SF on the first occasion only. ALLOW ≥ 2SF

ACCEPT

REJECT

MARK

(i)

20.0 = 0.0787 (moles) 254

0.079 / 0.07874

(1)

(ii)

1 mol I2 → 2 mol C2H5I (1)

mole ratio implied in method OR Mass method e.g. 127g I forms 156g C2H5I 20g I forms 20x156 127 = 24.6 (g) (2)

(2)

Answer to (i) x 2 x 156 = 24.6 / 24.55 / 24.57 (g) (1) Correct answer with some working scores (2) If answer to c (i) not multiplied by 2 the 2nd mark only accessible if there is some attempt to work out a mole ratio or state a mole ratio in first part of calculation N.B. 156 x 20 will give the correct final value (0) 127 (iii)

16.7 24.6

x 100 = 67.9 / 67.98 / 68.0 (%)

CQ on (ii)

Yield > 100 %

(1)

Total 11 marks

8