Edexcel Chemistry A2 (student Book) Examzone.pdf

1 of 3 Examzone – Answers to Student Book tests

Student Book Unit 4 Test 1 Mark scheme (Chapters 1.1 to 1.5)

1 a (i) Colorimeter / spectrophotometer (1); calibrate the colorimeter to correlate with the iodine concentration (1) (ii) Titration (1); with sodium thiosulfate (1) (iii) No need for quenching / ‘you can get the graph directly’ / difficulty of accurate timing (1) (5) b (i) Constant (1) (ii) Zero (1) (iii) I2 is not involved in it (1) or reaction between propanone and H1 is rate-determining step (iv) Two (1)

(4)

c (i) Iodoform / triiodomethane (1) CH3COCH3 1 3I2 1 4NaOH → CH3COONa 1 CHI3 1 3NaI 1 3H2O (2) (allow (1) for correct organic products) (ii) CH3

CH3

C O

C

(2)

OH

(iii) Potassium dichromate turns green with alcohol, not with ketone (1) any test that works is acceptable

(Total 15 marks)

2 a Halving [RX] halves the rate, so first order w.r.t. RX (1) Halving [OH2] halves the rate, so first order w.r.t. OH2 (1) explanation of either statement (1) So, rate 5 k[RX][OH2] (1)

(3)

26 5 ___________ ​  8 3 10    ​5 0.0215 (1) dm3 mol21 s21 (1) b k 5 ___________ ​  rate 2  ​    [RX][OH ] 0.01 3 0.04

(2)



(Total 5 marks)

3 a incompletely / partially / slightly dissociated (1) or dissociation varies with concentration allow poor proton donor or conjugate base strong

(1)

b (i) CH3CH2COOH ⇋ CH3CH2COO2 1 H1 or CH3CH2COOH 1 H2O ⇋ CH3CH2COO2 1 H3O1 (1) [CH3CH2COO2] [H3O1] [CH3CH2COO2] [H1] _______________________  ​or ​   ​(1) Ka 5 ____________________ ​               [CH3CH2COOH [CH3CH2COOH] Mark consequentially for second mark if acid is incorrect but must have H1 or H3O1 __________________ c   ​5 √ ​  1.30 3 1025 3   0.01 ​5

______

(ii) [H ] 5 √ ​  Ka 3 3.6 3 10 (mol dm ) (1) 1 24 pH 5 2log [H ] 5 2log(3.6 310 ) 5 3.4 (1) Any of: • any rounding should be consistent • assumes dissociation of acid is small / concentration of acid does not change (1) if made no assumptions i.e. solved quadratic and got correct answer (3) penalise arithmetic errors once only 1

218

(6)

24

(2)

23

(3)

Examzone – Answers to Student Book tests 2 of 3

Student Book Unit 4 Test 1 Mark scheme (cont.)

(iii) pH down means [H1] up (1) Dissociation endothermic (1) Equilibrium shifts in endothermic direction when temperature rises (1) mark consequentially

(3)

(Total 9 marks)

1   ​  (1) 4 a (i) pH 5 2log [H1] or log ​ _____ [H1] (ii) Kw 5 [H1] [OH2] (1)  accept [H3O1] instead of [H1]

(2)

b (i) [H1] 5 0.200 mol dm23; pH 5 0.70 (1) allow caveat or appropriate better chemistry, e.g. cannot be calculated because Ka not given if calculated as a monobasic acid they must explain why 214 5 2 3 10213 (mol dm23) (1); (ii) [OH2] 5 0.0500 mol dm23 ; [H1] 5 _________ ​ 1 3 10  ​    0.05 pH 5 12.7 (1) (3) not 13 allow calculation from pOH 5 1.3, allow even if called pH penalise 4 or more significant figures mark consequentially if answer higher than 7 but less than 15

c (i) maintains pH nearly constant if small amounts of acid or base added (1) accept resists change to pH [H1] [CH3COO2] __________ [H1] [salt]  ​5 ​   ​  (1) (ii) Ka 5 1.8 3 1025 5 ________________ ​          [CH3COOH] [acid] [H1] 5 1.8 3 1025 3 ______  ​5 4.91 3 1026 (mol dm23) (1) ​ 0.015  0.055 pH 5 2log 4.91 3 1026 5 5.3 (1) Mark consequentially if salt and acid wrong way up Incorrect if used 0.015 twice but would get final mark consequentially

(Total 9 marks)

5 a Reacts in both directions (1); at equal rates (1) must mention rates for second mark

(2)

b 70–200 atm (1); high pressure moves equilibrium to right (1) 350–550  °C (1); low temperature moves equilibrium to right (1) but rate too slow (1); (so use) iron or iron oxide catalyst (1) if no other marks awarded high pressure and low temperature (1) if both given c Makes it happen faster (1); no effect on equilibrium position (1) give mark if mentioned in part b

(4)

(max 5) (2)

(Total 9 marks)

219

3 of 3 Examzone – Answers to Student Book tests

Student Book Unit 4 Test 1 Mark scheme (cont.)

6 a Correct expression for Kp (1); no units or no square brackets

atm2 atm2

(1)

(2)

b (i) Mole fraction HI 5 0.78, H2 5 I2 5 0.11 (1) Partial pressure HI 5 1.56 atm (1); H2 5 I2 5 0.22 atm (1)

(3)

2 (ii) Kp 5 _____ ​ 1.562 ​  (1) (consequential on values in part b (i) and expression in part a) 0.22 5 50.28 or 50.3 or 50 (1) (2)

c (i) 2Na2S2O3 1 I2 → Na2S4O6 1 2NaI; species (1); balanced (1) balancing mark conditional on correct species ionic equation acceptable

(2)

(ii) Starch (1); blue/black to colourless (1) not white or clear in place of colourless

(2)

(iii) Ease of discernibility compared (1); Actual colour change for iodine / thiosulfate – i.e. yellow → colourless (1)

220

(2)

(Total 13 marks)

Examzone – Answers to Student Book tests 1 of 3

Student Book Unit 4 Test 2 Mark scheme (Chapters 1.6 to 1.7)

1 a Object and mirror-image are non-superimposable / contains a carbon atom with four different groups (1) (1) accept asymmetric molecule not asymmetric carbon atom or rotates the plane of polarised light b (i) Rotates (plane of polarisation of) plane-polarised (monochromatic) light or has a non-superimposable mirror image (1) not bends/twists light if they say ‘contains chiral carbon’ this must be explained or indicated on the diagram for (1) (ii)

CH2CH3 C CH3

CH2CH3

Br

Br

C H

H

CH3

Structure (1); correct mirror image (1) must be 3D drawing for (2) – if it is drawn flat only (1) if a correct mirror image of an incorrect but chiral compound then (1) – the chiral compound must be feasible to get this mark

(3)

c (i) A species with a lone pair of electrons to donate (1) not ‘seeks protons in nucleus’ or ‘nucleus loving’ or ‘has a negative charge’ (ii) CH3CH2CH(OH)CH3 (1) consequential alcohol on answer to part b (ii) the structure must be sufficiently clear to show butan-2-ol H H H H is OK H

C

C

C

C

H

H

OH H

H

(iii) Add PCl5 (1); (steamy) (acid) fumes / white gas (1) if PCl5(aq) then (0) any other suitable test and result acceptable e.g. sodium (1); bubbles (1) potassium dichromate(VI) (1); green (1) potassium manganate(VII) (1); brown/colourless (1) add carboxylic acid and conc. sulfuric acid (1); sweet smell (1) I2/NaOH or KI/NaClO (1); yellow ppt. (1) consequential on answer given to part c (iii)

(4)

d (i) hydrolysis / saponification (1) not substitution (ii) Yield falls; reaction with acid is an equilibrium (1)

(2)

e (i) Ethanoic acid (1) (ii) CH3COOH / CH3COO2 (1) (iii) HCl/H3O1 is a stronger acid (1) than ethanoic acid (1) or CH3COO2 strong base (1) whereas Cl2 weaker base (1)

(4) (Total 14 marks)

221

2 of 3 Examzone – Answers to Student Book tests

Student Book Unit 4 Test 2 Mark scheme (cont.)

2 a A – F – G – C – D – E – B (2) (1) if one letter out of sequence but rest correct; (0) if two or more letters out of sequence if adjacent pair inverted this is one error. b Little – to produce a saturated solution / to prevent loss of solid / because all solid will not crystallise / to prevent loss of yield. (1) Small – (if large volume used) solid would be lost/dissolved (1)

(2)

(2) (Total 4 marks)

3 a Reasoning/identification of peaks: 3 types of H ratio 6 : 1 : 1 or some correct reference to height of peaks (1) this related to structure of propan-2-ol in shift data (1)

(2)

b Yellow ppt. (1); hospital smell (1)

(2)

c

(1)

O CH3

CH3CH2 O

(1)

CH CH3

d Propene (1); dehydration/elimination (1)

(2) (Total 7 marks)

4 a (Wear) gloves / add slowly / cool while adding (1) if multiple answers correct and incorrect (0) not lab. coat / be careful not to spill on hands / do in a fume cupboard

(1)

b (i)

WATER OUT

WATER IN

HEAT

NOT arrow on its own

Flask (round or pear shaped only) 1 heat (1) Vertical condenser (double surface and water inlet and outlet) (1) not sealed, no gaps, joint shown between flask and condenser safe not distillation, if water in/out labelled they must be correct

222

(2)

Examzone – Answers to Student Book tests 3 of 3

Student Book Unit 4 Test 2 Mark scheme (cont.)

(ii) (Fractionally) distil (1) Collect fraction that distils over at about 56  °C / stated range 55–57  °C or 54–58  °C (1) a temperature value / range must be quoted not ‘collect fraction above 56  °C’ mark independently c PCl5 / SOCl2 (1); no steamy fumes / no gas which turns blue litmus red (1) or K2Cr2O7 1 H2SO4 (1); no colour change / stays orange (1) or KMnO4 1 H2SO4 (1); no colour change / stays purple (1) or Na (1); no bubbles / no effervescence (1) name or formula can be given ignore oxidation numbers unless they are incorrect results may be given as negative tests – or as ‘if propan-2-ol was present there would be steamy fumes’ result mark is dependent on correct reagent but may have result mark if minor error in reagent must be a chemical test – e.g. not ‘check that boiling point is 56  °C exactly’

(2)

(2)

(Total 7 marks)

223

1 of 3 Examzone – Answers to Student Book tests

Student Book Unit 5 Test 1 Mark scheme (Chapters 2.1 to 2.2)

1 a (i) 12 to 12.5 (or 0.5) (1) I2 1 2S2O322 → S4O6221 2I2 (1) allow S4O622 1 2I2 ⇋ I2 1 2S2O322 but not S4O622 1 2I2 → I2 1 2S2O322

(2)

(ii) 12 to 16 (or 4) (1) 4XCl2 1 2S2O322 1 5H2O → 8Cl2 1 2SO422 1 10H species (1); balanced (1) allow 8Cl2 1 2SO422 1 10H1 ⇋ 4Cl2 1 2S2O322 1 5H2O but not 8Cl2 1 2SO422 1 10H1 → 4Cl2 1 2S2O322 1 5H2O if the equations are given the wrong way round with an → but the oxidation number changes are given correctly for these equations as –0.5 and –4 then the 2 oxidation state marks can be given

(3)

b The colour change is not sharp / not easy to see (1); no suitable indicator (1) or bromine is volatile / is lost from the system (1); therefore results are not accurate / reliable (1)

(2)

(Total 7 marks)

2 a Potential / e.m.f. / voltage / half-cell of electrode (1); relative to (standard) hydrogen electrode (1); solutions of unit concentration (1); and gases at 1  atm / standard temperature (1)

(max 2)

b Voltmeter requires two connections / measure potential difference (1); and so another electrode is introduced into system (1)  allow ‘for redox has to have a source / sink of electrons’ (1)

(2)

c (i) Reaction in which a given species / substance / molecule / ion is simultaneously / both oxidised and reduced (1) not atom (ii) Ecell  for disproportionation is 11.23 V 2 (11.70 V) 5 20.47 V (1) or equivalent in words (1) (This is negative) so reaction does not occur (1) second mark is consequential on the first statement

(3) (Total 7 marks)

3 a (i) Cu 1 4H1 1 2NO32 → Cu21 1 2NO2 1 2H2O; species (1); balanced (1) or similar reaction with Zn or Ni balancing mark conditional on correct species (ii) Redox (1)

(3)

b (i) [Cu(H2O)6]21; [Ni(H2O)6]21; [Zn(H2O)6]21 or [Zn(H2O)4]21 3 correct (2); 2 correct (1); 1 correct (0) (ii) Cu(OH)2 (1); Ni(OH)2 (1) ignore any hydration if Zn(OH)2 is included then (21) (iii) [Zn(OH)4]22 or [Zn(OH)3]2 or ZnO222 (1) ignore any hydration in the first two, but the last must not include any hydration not [Zn(OH)6]42 224

(5)

Examzone – Answers to Student Book tests 2 of 3

Student Book Unit 5 Test 1 Mark scheme (cont.)

c (i) e.g. [Cu(H2O)6]21 1 2OH2 → Cu(OH)2 1 6H2O; species (1); balanced (1) balancing mark conditional on correct species H2Os on right-hand side must add up to 6 (ii) deprotonation or acid–base (1) not hydrolysis or precipitation

(3)

d NaOH to remove nitric acid (1); which would interfere with the redox reaction or would oxidise iodide ions or solution must be acidic to keep Cu21 ions in solution (1) Quality of language (1)

(3)

e (i) 2Na2S2O3 1 I2 → Na2S4O6 1 2NaI (1) or Na2S2O3 1 _​ 12 ​I2 etc. accept ionic equation Add starch when solution pale yellow (1) not towards the end point If added too soon gives ppt. or insoluble complex (1)

(3)

 ​  (1) (ii) No. of moles S2O322 5 __________ ​ 0.1 3 18.7   1000 relate to moles Cu21 (equation or statement) (1) no. of moles Cu21 5 1.87 3 1023 in 25 cm3 So no. of moles Cu21 5 1.87 3 1023 3 20 in 500 cm3 (1) mass Cu21 5 no. of moles in 500 cm3 3 63.5 g in 500 cm3 5 2.375 g (1) 2.375 3 ​ 100   5 25.0% (24.99) (1)  So, %Cu 5 ​ ____________    9.5 25.0% and some working scores (5) if reaction stoichiometry is incorrect then (max 4) (iii) Comment on relative magnitude of E   values (1) So, Cu21 should not oxidise I2 to I2 (under standard conditions) (1) relevance of insolubility of CuI (1) 4 Coloured ions / compounds (1) (not metals) complex ions / form complexes (1) paramagnetic ions / compounds (1) variable valency or oxidation state (1) catalytic activity (1) high melting or boiling temperature / high density (1) not part filled d-shells or just ‘paramagnetism’

(5)

(3)

(Total 25 marks)

(max 3) (Total 3 marks)

225

3 of 3 Examzone – Answers to Student Book tests

Student Book Unit 5 Test 1 Mark scheme (cont.)

5 a (i) Deprotonation (1) (ii) Ligand exchange / transfer / complex (ion) formation (1) b Cu(OH)2 (1) accept up to four water molecules in addition

(1)

c [Cu(NH3)4]21 (1) planar drawn (1); not tetrahedral or [Cu(NH3)4(H2O)2]21 (1) octahedral (1) or [Cu(NH3)6]21 (1) octahedral (1) allow any of 1 to 6 NH3 with 5 to 0 H2O to balance

(2)



(Total 5 marks)

6 a Not all d orbitals full / incomplete d orbitals (1) b dative (covalent), co-ordinate (1) and covalent (1) if ionic or metallic given with other types of bonding (21)

226

(2)

(1) (2) (Total 3 marks)

Examzone – Answers to Student Book tests 1 of 2

Student Book Unit 5 Test 2 Mark scheme (Chapters 2.3 to 2.5)

1 a Delocalised bonding in benzene (1) Benzene does not have three (localised) C Benzene ring has high stability (1) Less susceptible to addition (1)

C bonds (1) (max 2)

b (i) Concentrated acids (1); lower than 60  °C (1)

(2)

(ii) HNO3 1 2H2SO4 ⇋ NO2 1 2HSO3 1 H3O (1) or HNO3 1 H2SO4 ⇋ H2NO31 1 HSO42 or HNO3 1 H2SO4 ⇋ NO21 1 HSO42 1 H2O Sulfuric acid donates H1 to nitric acid (1)

(2)

(iii) (1) allow this mark also for

(2)

1

2

H�

H �

NO2

at end

NO2

NO2

�

� H�

(1) for plus charge and incomplete ring delocalisation or equivalent using Kekulé forms – intermediate should have two double bonds only (iv) Addition destroys delocalisation substitution does not (1)

(1) (Total 9 marks)

2 a Fume cupboard (1); gloves (1) safety requirements must be specific to question

(2)

b C6­H5NH­1 HCl → C6H5NH31Cl2 (1) must have correct charges ignore Cl2 if H1 on left-hand side

(1)

c (i) Too slow lower than 0  °C (1); product decomposes at higher than 5  °C (1) (ii) Exothermic (1); have to keep temperature below 5  °C (1)

(4)

d 

(2) N2�Cl� �

N

N

� HCl ignore HCl

reactants (1)

products (1)

allow N N or N N 1 but not N N or N N1 2 Cl not essential 1

1

(Total 9 marks)

3 a (i) Chlorine (1); sunlight / u.v. light (1); C6H5CH3 1 Cl2 → C6H5CH2Cl 1 HCl (1) the first condition mark can be awarded if u.v. light / sunlight is mentioned in part (ii) condition dependent on reagent allow C7H8 1 Cl2 etc. (ii) Fractional distillation (1); distil off methylbenzene and distil a sample of benzyl chloride / (chloromethyl) benzene at 179  °C (1) (5) b HCl (1); room temperature (1) CH3CH2CH2NH2 1 HCl → CH3CH2CH2NH31Cl2 (1)

(3) (Total 8 marks) 227

2 of 2 Examzone – Answers to Student Book tests

Student Book Unit 5 Test 2 Mark scheme (cont.)

4 a (i)

(ii)

H

CH3

C

C

Cl

H

H

CH3

C

C

(1) NH2

(1) N�H3(Cl�)

OH H

(iii)

H

CH3

C

CH

(2) NHCOCH3

OCOCH3

if two structures are given each one should have one of the groups acylated (2) if just the ring acylated then (1) – position does not matter if the ring and one group acylated (2) (iv)

(1)

COOH

allow the sodium salt – charges not necessary allow the anion (v)

H

CH3 C

(1)

(6)

C NH3� (HSO4�)

structure must be unambiguous allow the free amine not an ether or substitution of SO3H b (i) Fume cupboard / open window (1); gloves (1) (ii) Dissolve in minimum volume trichloromethane (1); boiling/hot solvent (1); hot filter (1) cool (1); filter and dry crystals (1) if give cool and filter (0) if nothing sensible given before (iii) Melting temperature (1); sharp or compare with known value (1)

(9)

(Total 15 marks)

5 a (i) Na in EtOH / LiAlH4 / hydrogen (1); not sodium borohydride Correct condition for reagent used (1); i.e. room temp or warm for Na in EtOH / dry ether for LiAlH4 / Pt or Ni catalyst for hydrogen C2H5CN 1 H2 → C2H5CH2NH2 (1) (3) using [H] or H2 acceptable but if using hydrogen gas must show as H2 (ii) Reagent: CH3COCl (1); at room temperature (1); C2H5CH2NH2 1 CH3COCl → C2H5CH2 NHCOCH3 1 HCl (1) 228

b The reaction is used in the synthesis of paracetamol (1)

(3) (1)

(Total 7 marks)