MARK SCHEME for the October/November 2015 series 9701 CHEMISTRY. 9701/11 Paper 1 (Multiple Choice), maximum raw mark 40

Transcription

1 CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 205 series 970 CHEMISTRY 970/ Paper (Multiple Choice), maximum raw mark 40 Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the October/November 205 series for most Cambridge IGCSE, Cambridge International A and AS Level components and some Cambridge O Level components. IGCSE is the registered trademark of Cambridge International Examinations.

2 Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Number Key Question Number Key C 2 C 2 A 22 D 3 B 23 B 4 A 24 C 5 C 25 D 6 D 26 A 7 B 27 D 8 D 28 B 9 B 29 B 0 B 30 B C 3 C 2 A 32 B 3 A 33 B 4 A 34 D 5 D 35 B 6 D 36 A 7 B 37 C 8 A 38 C 9 A 39 D 20 C 40 B Cambridge International Examinations 205

3 CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 205 series 970 CHEMISTRY 970/2 Paper (Multiple Choice), maximum raw mark 40 Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the October/November 205 series for most Cambridge IGCSE, Cambridge International A and AS Level components and some Cambridge O Level components. IGCSE is the registered trademark of Cambridge International Examinations.

4 Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Number Key Question Number Key B 2 B 2 C 22 D 3 D 23 A 4 A 24 A 5 D 25 C 6 A 26 D 7 C 27 B 8 C 28 C 9 B 29 A 0 C 30 A C 3 D 2 D 32 A 3 B 33 D 4 D 34 C 5 B 35 D 6 A 36 B 7 D 37 C 8 D 38 C 9 C 39 B 20 B 40 A Cambridge International Examinations 205

5 CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 205 series 970 CHEMISTRY 970/3 Paper (Multiple Choice), maximum raw mark 40 Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the October/November 205 series for most Cambridge IGCSE, Cambridge International A and AS Level components and some Cambridge O Level components. IGCSE is the registered trademark of Cambridge International Examinations.

6 Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Number Key Question Number Key C 2 C 2 A 22 D 3 B 23 B 4 A 24 C 5 C 25 D 6 D 26 A 7 B 27 D 8 D 28 B 9 B 29 B 0 B 30 B C 3 C 2 A 32 B 3 A 33 B 4 A 34 D 5 D 35 B 6 D 36 A 7 B 37 C 8 A 38 C 9 A 39 D 20 C 40 B Cambridge International Examinations 205

7 CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 205 series 970 CHEMISTRY 970/2 Paper 2 (AS Structured Questions), maximum raw mark 60 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the October/November 205 series for most Cambridge IGCSE, Cambridge International A and AS Level components and some Cambridge O Level components. IGCSE is the registered trademark of Cambridge International Examinations.

8 Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Mark Scheme Mark Total (a) regular arrangement / lattice of cations / positive ions surrounded by delocalised electrons [2] (b) (i) electrical conductor corrosion resistant low density ductile owtte [max2] (ii) Giant / lattice (iii) (electrical) insulator (c) (i) Simple covalent / covalent molecule Weak intermolecular forces / VdW forces OR little energy needed to break down / overcome intermolecular / VdW forces [2] (ii) Al Cl AlCl 3 [2] Cambridge International Examinations 205

9 Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Mark Scheme Mark Total (iii) pv = m M r RT mrt M = pv = = 267 r 3 6 OR pv = nrt n = pv RT = = [2] M.36 = r = (iv) Al 2Cl 6 [3] 2 (a) (i) The enthalpy change when one mole of a compound is formed from its element(s) [2] (ii) S(s) + ½O 2 (g) SO 3 (l) (b) (i) (3 436) = = = 88 (kj mol ) [3] (ii) Fe catalyst 200 atm ( )C [3] (iii) High T increases rate AND Low T improves yield owtte Chosen temp is a compromise High P favours / increases (both rate and) yield owtte pressure chosen limited by cost (of compression and thick walls ) [4] Cambridge International Examinations 205

10 Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Mark Scheme Mark Total (c) (i) 2NH 3 + H 3 PO 4 (NH 4 ) 2 HPO 4 (ii) (d) (i) (ii) NH 3 identified as base AND H 3 PO 4 identified as acid base accepts protons AND acid donates protons nitrates / fertilisers wash into rivers eutrophication / algal bloom / promote algal growth bacteria use up oxygen in decay process (oxides of nitrogen / NO x / NOs) cause acid rain [2] [3] 2NO 2 + H 2 O HNO 2 + HNO 3 OR 4NO 2 + 2H 2 O + O 2 4HNO 3 OR SO 2 + NO 2 SO 3 + NO AND SO 3 + H 2 O H 2 SO 4 3 (a) (i) structural isomers: (different molecules with) same molecular formula but different structural formulae chiral: has a carbon / C attached to 4 different groups / atoms / chains OR has no plane / line of symmetry / has non-superimposable mirror images (ii) CH 3 CH 2 CH(CH 3 )CH 2 CH 2 CH 3 3-methylhexane CH 3 CH(CH 3 )CH(CH 3 )CH 2 CH 3 / (CH 3 ) 2 CHCH(CH 3 )CH 2 CH 3 2,3-dimethylpentane [2] [2] [2] [4] (b) (i) C 7 H 6 + O 2 7CO 2 + 8H 2 O (ii) C 7 H 6 + 4O 2 7C + 8H 2 O Cambridge International Examinations 205

11 Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Mark Scheme Mark Total (iii) global dimming / PAN / smog / global warming (c) (i) (Free) Radical Substitution (ii) Cl 2 2Cl OR Cl 2 Cl + Cl C 7 H 6 + Cl C 7 H 5 + HCl C 7 H 5 + Cl 2 C 7 H 5 Cl + Cl C 7 H 5 + Cl C 7 H 5 Cl OR C 7 H 5 + C 7 H 5 C 4 H 30 Initiation; Propagation; Termination (used correctly) [5] [5] 4 (a) (i) CH 3 CH 2 OH + HCl CH 3 CH 2 Cl + H 2 O or CH 3 CH 2 OH + PCl 5 CH 3 CH 2 Cl + HCl + POCl 3 or CH 3 CH 2 OH + SOCl 2 CH 3 CH 2 Cl + HCl + SO 2 [+] [2] (ii) NaOH / KOH warm / heat / reflux AND aqueous [2] (b) (i) CH 2 =CH 2 / ethane / C 2 H 4 / CH 2 CH 2 (ii) White ppt / solid / suspension (iii) Ag + (aq) + Cl (aq) AgCl (s) (c) (i) CH 3 CHO / ethanal Cambridge International Examinations 205

12 Page 6 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Mark Scheme Mark Total (ii) CH 3 CH 2 OH higher bpt than CH 3 CHO ora due to hydrogen bonding in ethanol / stronger IMFs prevents further oxidation owtte [3] [] Cambridge International Examinations 205

13 CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 205 series 970 CHEMISTRY 970/22 Paper 2 (AS Structured Questions), maximum raw mark 60 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the October/November 205 series for most Cambridge IGCSE, Cambridge International A and AS Level components and some Cambridge O Level components. IGCSE is the registered trademark of Cambridge International Examinations.

14 Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Mark Scheme Mark Total (a) name of isotope type of particle charge symbol electron configuration 3 carbon-3 atom 0 6 C s 2 2s 2 2p 2 chloride(-37) anion Cl s 2 2s 2 2p 6 3s 2 3p 6 [5] [5] 34 sulfur-34 atom 0 6 S s 2 2s 2 2p 6 3s 2 3p 4 iron-54 cation (2 ) 26 Fe + s 2 2s 2 2p 6 3s 2 3p 6 3d 6 (b) (i) ability / tendency / power of an atom / nucleus to attract / pull electron(s) in a covalent bond / shared pair of electrons / bonding pair of electrons [2] (ii) Covalent overlap of orbitals OR shared pair(s) (of electrons) OR metallic positive ions / cations surrounded by delocalised electrons [2] (iii) Ionic/electrovalent (electrostatic) Attraction between oppositely charged / +ve and ve ions [2] (c) (i) similar strength / amount / number of intermolecular forces / induced dipole / van der Waals / VdW / London forces / LDF / dispersion forces [2] therefore similar energy needed Cambridge International Examinations 205

15 Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Mark Scheme Mark Total (ii) M HCl polar / has a dipole AND F 2 non-polar / has no dipole OR (permanent) dipole (-dipole) attractions / forces between HCl (molecules) AND induced dipole (-induced dipole) attractions / forces / LDFs between F 2 (molecules) M2 more energy needed for HCl than F 2 OR pd-pd forces stronger than id-id forces OR IMFs / VdWs in HCl stronger than in F 2 [2] (iii) Hydrogen bonding (between methanol molecules) Stronger than IMFs / van der Waals in other three / is the strongest intermolecular force [2] [7] 2 (a) M Heat (energy) change (or H prod H react ) measured at constant pressure OR enthalpy change when the amount/moles of reactants as shown in a (reaction) equation react together to give products M2 measured at standard conditions [2] (b) (i) q = (ii) amount = 0.025(0) (iii) 85.(0) Cambridge International Examinations 205

16 Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Mark Scheme Mark Total (iv) ( MgSO 4 (s) + 7H 2 O(l) MgSO 4.7H 2 O(s) ) 85.0 (kj mol ) (+)9.60 (kj mol ) MgSO 4 (aq) (v) H = 85.0 H = = 94.6 (kj mol ) 3 (a) (i) Na 2 O or Na 2 O 2 ; MgO; P 4 O 0 or P 4 O 6 ; SO 2 [7] [2] (ii) Na: Yellow / orange / gold flame / white solid / powder / smoke 4Na + O 2 2Na 2 O or 2Na + O 2 Na 2 O 2 S: Blue flame / (yellow) solid melts / turns red / amber / white fumes S + O 2 SO 2 [4] (b) (i) acidic P and S amphoteric Al and basic Na and Mg [2] (ii) acidic: covalent (bonding) basic: ionic (bonding) [2] Cambridge International Examinations 205

17 Page 5 Mark Schemee Cambridge International AS/ /A Level October/November 205 Syllabus 9709 Paper 222 Question Markk Scheme Mark Total (iii) Al 2 O 3 + 6HC6 Cl 2AlCl Al 2 O 3 + 6H 6 + 2Al H 2 O OR + 3H 2 2O Al 2 O 3 Al 2 O 3 Al 2 O 3 Al 2 O 3 Al 2 O 3 Al 2 O NaOH + 7HH 2 O 2NaOH + 3HH 2 O 2NaAl (OH) 4 (H 2 O) O 2 OR 2NaAl (OH) 4 ORR 2NaOH 2NaAlO2 + H 2 O ORR 2OH 2OH 2OH + 7H7 2 O 2[Al( 2 (OH) 4 (HH 2 O) 2 ] + 3H3 2 O 2[Al( 2 (OH) 4 ] OR 2AlO2 O 2 + H 2 O ORR [2] (c) sulfurr formss SOO 2 / SO 2 + / mixem es H 2 O H 2 SOS 3 or in wordss OR SOO 2 + / mixesm s H 2 2O ( a( acid) / or in words OR SOO 2 + / mixesm s H 2 2O + (/2O2) H 2 SO4 / or r in words [2] [4] 4 (a) (i) Nucleophilic Substitution (ii) Has a chiral centre / carbon ORR has a carbon / C attached to 4 different groups / atoms / chainss OR has no planee / line of o symmetryy (iii) [+ +] [2] (iv) Elimination Cambridgee International ExamE minations 205

18 Page 6 Mark Schemee Cambridge International AS/ /A Level October/November 205 Syllabus 9709 Paper 222 Question Markk Scheme Mark Total (v) [2] (vi) But--ene 2 Hs on one o of the double-bondedd groups on bothb h atomss / each atomm inn C= Css OR does not have 2 different =C [2] (b) (i) ammoniaa / N H 3 (ii) propanoyl chloride / C 2 H 5 COCl (iii) CH 3 CH(NHCOCC 2 H5)CH 5 H 3 (iv) Reduction LiAlHH 4 / NaBHN H 4 / H 2 and a Ni / tin andd concentrated HCl [2] (v) aluminiumm oxide Cambridgee International ExamE minations 205

19 Page 7 Mark Schemee Cambridge International AS/ /A Level October/November 205 Syllabus 9709 Paper 222 Question Markk Scheme Mark Total (vi) [4] M = correctt structure of Y and curly arrow fromm double bond to H M2 = dipole and curly arrow from H-Br bond to Br M3 = correctt intermediate M4 = Br with lone pairr and curly arrow from lone pair to C(+) C ) (vii) electrophilic addition (viii) secondary carbocation more stabs ble than primary due too electron releasing character /(pos( sitive) inductive effect of alkya yl groups [2] [22] Cambridgee International ExamE minations 205

20 CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 205 series 970 CHEMISTRY 970/23 Paper 2 (AS Structured Questions), maximum raw mark 60 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the October/November 205 series for most Cambridge IGCSE, Cambridge International A and AS Level components and some Cambridge O Level components. IGCSE is the registered trademark of Cambridge International Examinations.

21 Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Mark Scheme Mark Total (a) regular arrangement / lattice of cations / positive ions surrounded by delocalised electrons [2] (b) (i) electrical conductor corrosion resistant low density ductile owtte [max2] (ii) Giant / lattice (iii) (electrical) insulator (c) (i) Simple covalent / covalent molecule Weak intermolecular forces / VdW forces OR little energy needed to break down / overcome intermolecular / VdW forces [2] (ii) Al Cl AlCl 3 [2] Cambridge International Examinations 205

22 Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Mark Scheme Mark Total (iii) pv = m M r RT mrt M = pv = = 267 r 3 6 OR pv = nrt n = pv RT = = [2] M.36 = r = (iv) Al 2Cl 6 [3] 2 (a) (i) The enthalpy change when one mole of a compound is formed from its element(s) [2] (ii) S(s) + ½O 2 (g) SO 3 (l) (b) (i) (3 436) = = = 88 (kj mol ) [3] (ii) Fe catalyst 200 atm ( )C [3] (iii) High T increases rate AND Low T improves yield owtte Chosen temp is a compromise High P favours / increases (both rate and) yield owtte pressure chosen limited by cost (of compression and thick walls ) [4] Cambridge International Examinations 205

23 Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Mark Scheme Mark Total (c) (i) 2NH 3 + H 3 PO 4 (NH 4 ) 2 HPO 4 (ii) (d) (i) (ii) NH 3 identified as base AND H 3 PO 4 identified as acid base accepts protons AND acid donates protons nitrates / fertilisers wash into rivers eutrophication / algal bloom / promote algal growth bacteria use up oxygen in decay process (oxides of nitrogen / NO x / NOs) cause acid rain [2] [3] 2NO 2 + H 2 O HNO 2 + HNO 3 OR 4NO 2 + 2H 2 O + O 2 4HNO 3 OR SO 2 + NO 2 SO 3 + NO AND SO 3 + H 2 O H 2 SO 4 3 (a) (i) structural isomers: (different molecules with) same molecular formula but different structural formulae chiral: has a carbon / C attached to 4 different groups / atoms / chains OR has no plane / line of symmetry / has non-superimposable mirror images (ii) CH 3 CH 2 CH(CH 3 )CH 2 CH 2 CH 3 3-methylhexane CH 3 CH(CH 3 )CH(CH 3 )CH 2 CH 3 / (CH 3 ) 2 CHCH(CH 3 )CH 2 CH 3 2,3-dimethylpentane [2] [2] [2] [4] (b) (i) C 7 H 6 + O 2 7CO 2 + 8H 2 O (ii) C 7 H 6 + 4O 2 7C + 8H 2 O Cambridge International Examinations 205

24 Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Mark Scheme Mark Total (iii) global dimming / PAN / smog / global warming (c) (i) (Free) Radical Substitution (ii) Cl 2 2Cl OR Cl 2 Cl + Cl C 7 H 6 + Cl C 7 H 5 + HCl C 7 H 5 + Cl 2 C 7 H 5 Cl + Cl C 7 H 5 + Cl C 7 H 5 Cl OR C 7 H 5 + C 7 H 5 C 4 H 30 Initiation; Propagation; Termination (used correctly) [5] [5] 4 (a) (i) CH 3 CH 2 OH + HCl CH 3 CH 2 Cl + H 2 O or CH 3 CH 2 OH + PCl 5 CH 3 CH 2 Cl + HCl + POCl 3 or CH 3 CH 2 OH + SOCl 2 CH 3 CH 2 Cl + HCl + SO 2 [+] [2] (ii) NaOH / KOH warm / heat / reflux AND aqueous [2] (b) (i) CH 2 =CH 2 / ethane / C 2 H 4 / CH 2 CH 2 (ii) White ppt / solid / suspension (iii) Ag + (aq) + Cl (aq) AgCl (s) (c) (i) CH 3 CHO / ethanal Cambridge International Examinations 205

25 Page 6 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Mark Scheme Mark Total (ii) CH 3 CH 2 OH higher bpt than CH 3 CHO ora due to hydrogen bonding in ethanol / stronger IMFs prevents further oxidation owtte [3] [] Cambridge International Examinations 205

26 CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 205 series 970 CHEMISTRY 970/3 Paper 3 (Advanced Practical Skills ), maximum raw mark 40 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the October/November 205 series for most Cambridge IGCSE, Cambridge International A and AS Level components and some Cambridge O Level components. IGCSE is the registered trademark of Cambridge International Examinations.

27 Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total (a) I Initial and final readings and titre value given for rough titre and initial and final readings for two (or more) accurate titrations (minimum of 2 2 box) II Titre values recorded for accurate titrations and Appropriate headings for the accurate titration table and cm 3 units. initial / start burette reading / volume / value final / end burette reading / volume / value (not amount) titre or volume / FA 4 and used / added unit: / cm 3 or (cm 3 ) or in cm 3 (for each heading) III All accurate burette readings are to the nearest 0.05 cm 3. Do not award this mark if: 50(.00) is used as an initial burette reading more than one final burette reading is 50.(00) any burette reading is greater than 50.(00) there is only one accurate titration. IV There are two uncorrected accurate titres within 0.0 cm 3 Do not award this mark if, having performed two titres within 0.0 cm 3, a further titration is performed which is more than 0.0 cm 3 from the closer of the initial two titres, unless a further titration, within 0.0 cm 3 of any other, has also been carried out. Do not award the mark if any accurate burette readings (apart from initial 0 cm 3 ) are given to zero dp Examiner rounds any burette readings to the nearest 0.05 cm 3, checks subtractions and then selects the best titres using the hierarchy: two (or more) accurate identical titres, then two (or more) accurate titres within 0.05 cm 3, then two (or more) accurate titres within 0.0 cm 3, etc These best titres are used to calculate the mean titre, expressed to nearest 0.0 cm 3. 3 Examiner calculates the difference (δ) between the mean titres obtained by the candidate and the Supervisor. Accuracy marks are awarded as shown. Award V, VI and VII if δ 0.20 (cm 3 ) Award V and VI if 0.20 < δ 0.30 Award V, only, if 0.30 < δ 0.50 [7] Spread penalty: if the two best (corrected) titres used by the Examiner were 0.50 cm 3 apart, cancel one accuracy mark. Cambridge International Examinations 205

28 Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total (b) Candidate must take the average of two (or more) titres that are within a total spread of not more than 0.20 cm 3. Working / explanation must be shown or ticks must be put next to the two (or more) accurate readings selected. The mean should be quoted to 2 dp, and be rounded to nearest 0.0 cm 3. Two special cases, where the mean need not be to 2 dp: Allow mean expressed to 3 dp only for or (e.g cm 3 ) Allow mean if expressed to dp, if all accurate burette readings were given to dp and the mean is exactly correct. (e.g and 26.2 = 26. is allowed) (e.g and 26. = 26. is wrong should be 26.05) Note: the candidate s mean will sometimes be marked correct even if it was different from the mean calculated by the Examiner for the purpose of assessing accuracy. (c)(i)(ii) Correctly calculates n(thio) = 0.0 (b) / 000 n(i 2 ) = 0.5 (i) Both answers must be given to 3 or 4 significant figures (iii) (iv) Correctly calculates n(kmno 4 ) = = or or Correct expression, with answer given to 2, 3 or 4 sig fig n(i 2 ) = (ii) / (iii) 2 Theoretical answer = 5.0 (for 2.0 mol KMnO 4 ) (v) Correct equation ticked, corresponding to (iv) (vi) Allow any one of the following answers: An iodide ion loses one electron 2I 2e I 2 (ionic equation must be correctly balanced) Oxidation number of iodine increases from / (in iodide ion) to 0 (in iodine) [5] (d) (i) % error = 0.06 / = 0.24 % (ii) The student is wrong, since KI / FA 3 is in excess. [2] Qn [Total: 5] 2 (a) I Table for readings, headings and correct units: Headings: volume of FA 5 / acid (volume of water if included must be correct) Time Units allow Vol or / cm 3 etc. Cambridge International Examinations 205

29 Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total II Three reaction times all recorded to nearest second III and IV Examiner to calculate the time differences between Expt and Expt 2 (t 2 t ). Then calculate 0% of the time for Expt to dp (x). If (t 2 t ).> x award III. Examiner to calculate the time differences between Expt 2 and Expt 3 (t 3 t 2 ). Then calculate 20% of the time for Expt 2 to dp (y). If (t 3 t 2 ).> y award IV. (b) (i) Rates correctly calculated All answers expressed to same sig fig (but not sf) Unit given... / s or (s ) 2 [4] (ii) Correctly calculates Expt, conc = (or or 0.086) mol dm 3 and Expt 3, conc = (or or 0.029) mol dm 3 Both answers must be given to 2, 3 or 4 sig figs (iii) Rate increases with (increase of) concentration (iv) Time is shorter for sulfuric acid Sulfuric acid has a greater / doubled concentration of H + ions. (v) time (for reaction) will be greater less depth (of solution) in the 250 cm 3 [5] Qn 2 [Total: 9] FA 6 is Na 2 SO 3 ; FA 7 is CaCl 2 ; FA 8 is MgSO 4 ; FA 9 is Al 2 (SO 4 ) 3 ; FA 0 is MnSO 4 3 (a) (i) Both observations required white precipitate with Ba 2+ ion Precipitate dissolves / partially dissolves in (excess) HCl (ii) Both observations required white precipitate with Ba 2+ ion precipitate insoluble / no change with HCl (iii) When heated, gas produced decolourises KMnO 4 paper. (iv) No change (when NaOH added) / no ppt / no reaction and green (solution) formed when KMnO 4 added Colourless solution(with acid) Cambridge International Examinations 205

30 Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total (v) Anion is sulfite and one piece of evidence FA 6 with acid SO 2 / gas which decolourises KMnO 4 is formed or FA 6 with Ba 2+ white precipitate / BaSO 3 formed which dissolves in acid / partially soluble in acid (vi) Na 2 SO 3 + H 2 O 2 Na 2 SO 4 + H 2 O [7] (b) (i) FA 7 FA 8 FA 9 FA 0 NaOH white ppt white ppt white ppt off-white / buff / beige / light brown ppt excess NaOH NH 3 excess NH 3 no change or insoluble in excess no ppt or no reaction (ignore) no change or insoluble in excess (ppt) dissolves or soluble in excess insoluble in excess or ppt darkens (owtte) white ppt white ppt off-white / buff / beige / light brown ppt no change or insoluble in excess no change or insoluble in excess insoluble in excess or ppt darkens (owtte) 5 (ii) Conclusions FA 7 calcium / Ca 2+ or barium/ba 2+ FA 8 magnesium / Mg 2+ FA 9 aluminium / Al 3+ FA 0 manganese(ii)/mn 2+ Four correct = 2 marks Two or three correct = mark (iii) M OH M(OH) 2 (for any divalent cation) or M OH M(OH) 3 (for any trivalent cation) 2 (iv) Use higher concentration [9] Qn 3 [Total: 6] Cambridge International Examinations 205

31 CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 205 series 970 CHEMISTRY 970/33 Paper 3 (Advanced Practical Skills ), maximum raw mark 40 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the October/November 205 series for most Cambridge IGCSE, Cambridge International A and AS Level components and some Cambridge O Level components. IGCSE is the registered trademark of Cambridge International Examinations.

32 Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total (a) I Initial and final readings and titre recorded for rough titre and accurate titre details tabulated (minimum 2 2 boxes ) II Headings and units correct for accurate titrations Headings: initial / final (burette) reading / volume or reading / volume at start / finish and titre or volume / FA 2 and added / used / titrated [not difference or total ] and Units: (cm 3 ) or / cm 3 or in cm 3 [or cm 3 by every entry] III All accurate burette readings are recorded to the nearest 0.05 cm 3 Do not award this mark if: 50(.00) is used as an initial burette reading; more than one final burette reading is 50(.00); any burette reading is greater than 50(.00) there is only one accurate titration IV Has two uncorrected, accurate titres within 0. cm 3 Do not award this mark if having performed two titres within 0. cm 3 a further titration is performed which is more than 0.0 cm 3 from the closer of the initial two titres, unless any further titrations, within 0. cm 3 of any other titration have also been carried out. Do not award the mark if any accurate burette readings (apart from initial 0) are given to zero dp. Examiner rounds any burette readings to the nearest 0.05 cm 3, checks subtractions and then selects the best titres using the hierarchy: two (or more) accurate identical titres then two (or more) accurate titres within 0.05 cm 3, then two (or more) accurate titres within 0.0 cm 3, etc. These best titres should be used to calculate the mean corrected titre to the nearest 0.0 cm 3. Examiner calculates the difference (δ) between the mean titres obtained by the candidate and the Supervisor. Accuracy marks awarded as shown. Award V, VI and VII if δ 0.30 cm 3 Award V and VI if 0.30 < δ 0.50 cm 3 Award V if 0.50 < δ 0.80 cm 3. Spread penalty: if the two best titres used by the Examiner were 0.5 cm 3 apart, cancel one accuracy mark. [7] Cambridge International Examinations 205

33 Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total (b) Candidate must average two (or more) accurate titres where the total spread is 0.20 cm 3. Working must be shown or ticks must be put next to the two (or more) accurate readings selected. The mean should normally be quoted to 2 decimal places rounded to the nearest 0.0. Two special cases where the mean may not be to 2 dp: allow mean to 3 dp only for or 0.075, e.g ; allow mean to dp if all accurate burette readings were given to dp and the mean is exactly correct. e.g and 26.2 = 26. is correct but 26.0 and 26. = 26. is incorrect. Note: the candidate s mean will sometimes be marked as correct even if it is different from the mean calculated by the Examiner for the purpose of assessing accuracy. (c) (i) Correctly calculates moles = (b) 0. / 000 and answer to 3 or 4 significant figures (ii) Same as (c)(i) (iii) Shows correct use of either factor of 40 (000 / 25) or mole ratio Answer consistent with data shown to 3 or 4 sf M r = 26.2 /( (c)(ii) 40) (iv) x = (M r 59.6) / 8 Answer to nearest positive integer with use of either 59.6 or 8 and some use of experimental data. [6] Qn Total [4] Cambridge International Examinations 205

34 Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total 2 (a) I Mass of FA 4 used by candidate was between.80 g and 2.00 g II Suitable table, with unambiguous headings and correct units, in parallel columns or rows and a minimum of four balance readings entered mass crucible / g (not weight) mass crucible + FA 4 (g) mass crucible + contents / FA 4 after heating in g mass crucible + contents / FA 4 after 2 nd / further heating / g III All balance readings (minimum 3) recorded to same dp and mass of FA 4 used and water lost correctly calculated IV Heating repeated until constant mass (final readings within 0.05 g for 2 dp balance and identical for dp balance) V and VI Examiner calculates and writes % next to table total mass water lost 00 Calculate to dp mass FA 4 Award V if % loss in range 2.8 to 6.8 Award VI if % loss in range 3.8 to 5.8 [6] (b) (i) Correctly calculated loss in mass / mass FA 4 to 2 4 sf (ii) Correctly calculates % loss = / 47. (iii) % purity = (i) 00 (ii) [3] (c) (Yes) because a greater mass used and so percentage error in weighing less. or (No) because there is more water to be lost so more spitting and frothing so percentage error in mass lost will be greater (d) Greater loss of mass therefore apparent % purity is high(er) / the value / it would increase Qn 2 Total [] Cambridge International Examinations 205

35 Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total FA 5 is Na 2 CO 3 (aq); FA 6 is H 2 SO 4 (aq); FA 7 is CH 3 COOH(aq); FA 8 is MnSO 4 (s) and MgCO 3 (s) 3 (a) (i) See table 4 FA 5 FA 6 FA 7 + Na 2 CO 3 no reaction effervescence / bubbling / fizzing or gas turns limewater milky / cloudy white / white ppt effervescence / bubbling / fizzing or gas turns limewater milky / cloudy white / white ppt + CuSO 4 blue ppt (not dark blue) no reaction / no change / no ppt / pale or light blue (solution) (not or no observation ) no reaction / no change / no ppt / pale or light blue (solution) (not or no observation ) + BaCl 2 / Ba(NO 3 ) 2 white ppt white ppt no reaction / no change / no ppt (ii) H + / hydrogen ion (iii) CO 3 2 / carbonate (iv) Cu 2+ (aq) + CO 3 2 (aq) CuCO 3 (s) [7] Cambridge International Examinations 205

36 Page 6 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November (b) (i) + NaOH: off white / buff / beige / pale or light brown (not cream) ppt and either darkens on standing or insoluble in excess + H 2 O 2 : (turns) brown / darker brown / brown-black (not black) fizzing / effervescence / bubbling or gas relights glowing splint (ii) + HNO 3 : fizzing / effervescence / bubbling or limewater turns milky / cloudy white / white ppt + NaOH: White ppt and insoluble in excess (iii) Mn 2+ / manganese(ii) and Mg 2+ / magnesium (iv) CO 3 2 / carbonate (v) Redox / decomposition of H 2 O 2 / disproportionation allow oxidation of Mn 2+ / oxidation or reduction of H 2 O 2 [8] Qn 3 Total [5] Cambridge International Examinations 205

37 CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 205 series 970 CHEMISTRY 970/34 Paper 3 (Advanced Practical Skills 2), maximum raw mark 40 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the October/November 205 series for most Cambridge IGCSE, Cambridge International A and AS Level components and some Cambridge O Level components. IGCSE is the registered trademark of Cambridge International Examinations.

38 Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total (a) I The following readings are recorded mass of Mg used two burette readings and the titre for the rough titration initial and final burette readings for two (or more) accurate titrations II Titre values recorded for accurate titrations and appropriate headings for the accurate titration table and cm 3 units. initial / start (burette) reading / volume final / end (burette) reading / volume titre or volume / FB 2 and used / added (not difference or total ) unit: / cm 3 or (cm 3 ) or in cm 3 (for each heading) If cm 3 units are not given in the headings, every entry in the table must have the correct unit. III All accurate burette readings are to the nearest 0.05 cm 3. Do not award this mark if: 50(.00) is used as an initial burette reading more than one final burette reading is 50.(00) any burette reading is greater than 50.(00) there is only one accurate titration. IV There are two uncorrected accurate titres within 0.0 cm 3 Do not award this mark if, having performed two titres within 0.0 cm 3, a further titration is performed which is more than 0.0 cm 3 from the closer of the initial two titres, unless a further titration, within 0.0 cm 3 of any other, has also been carried out. Do not award the mark if any accurate burette readings (apart from initial 0 cm 3 ) are given to zero dp Examiner checks and corrects titre subtractions where necessary. Examiner selects the best titres using the hierarchy: two (or more) accurate identical titres then two (or more) accurate titres within 0.05 cm 3, then two (or more) accurate titres within 0.0 cm 3, etc.these best titres are used to calculate the mean titre, expressed to nearest 0.0 cm 3. Examiner calculates the difference (δ) between the mean titres obtained by the candidate and the Supervisor. Accuracy marks are awarded as shown. Cambridge International Examinations 205

39 Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total Award V, VI and VII if δ 0.50 cm 3 Award V and VI if 0.50 < δ.00 cm 3 Award V, only, if.00 < δ.50 cm 3 Spread penalty: if the two best (corrected) titres used by the Examiner were 0.50 cm 3 apart, cancel one accuracy mark. 3 [7] (b) Candidate must take the average of two (or more) titres that are within a total spread of not more than 0.20 cm 3. Working / explanation must be shown or ticks must be put next to the two (or more) accurate readings selected. The mean should normally be quoted to 2 decimal places rounded to nearest 0.0 cm 3. Two special cases where the mean may not be to 2 dp: allow mean to 3 dp only for or 0.075, e.g ; allow mean to dp if all accurate burette readings were given to dp and the mean is exactly correct. e.g and 26.2 = 26. is correct but 26.0 and 26. = 26. is incorrect. Note: the candidate s mean will sometimes be marked correct even if it was different from the mean calculated by the Examiner for the purpose of assessing accuracy. (c) (i) mol NaOH = / 000 = 0.003(00) (ii) NaOH + HCl NaCl +H 2 O Answer to (ii) must be the same as in (i) (iii) + (iv) Correct expressions required in both (iii) and (iv) (Correct expression = correct figures shown) (iii) : no moles of HCl (in 250 cm 3 ) = (ii) 250 / (b) (iv) : no moles of HCl (in 25.0 cm 3 ) = / 000 (= 0.05) (v) Correct expression: Mol HCl used = (iv) (iii) (vi) Equation and correctly calculates answer for number of moles Mg: Mg(s) + 2HCl(aq) MgCl 2( aq) + H 2 (g) No of moles Mg = 0.5 (v) (vii) A r = mass of Mg used / (vi) [6] (d) (i) All solid / magnesium dissolved / disappeared / reacted (owtte) or indicator turned from blue to yellow when FB 2 added (to alkali) (ii) (If.0 g Mg is used) Mg would be in excess / acid would be the limiting reagent / all the acid would be used up Cambridge International Examinations 205

40 Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total Reference to moles of both acid and Mg (or other correct calculation) Calculation to show that Mg would be in excess n(mg) = / 24.3 = 0.04 mol (allow / 24 or / (c)(vii)) n(hcl) needed = mol or only 0.05 mol present Qn Total [7] Cambridge International Examinations 205

41 Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total 2 (a) I Table / list of data, showing the following: five unambiguous / clear headings accept mass of... or... / g (not weight ) accept mass of crucible + FB 4 after heating ignore omission of the crucible lid three balance readings, with unit shown at least once mass of water (or mass lost) mass of residue (owtte) all calculations must be correct All data must be written in the space provided Examiner should check calculations of masses of water and anhydrous MgSO 4. Examiner calculates the ratio mass of water lost / mass of residue to 2 dp The theoretical value is marks awarded for accuracy as shown. Award II if the ratio is between 0.80 and.5 (inclusive) Award III if the ratio is between 0.95 and.0 2 [3] (b) (i) Correctly calculates to 2 4 sf Number of moles = mass loss / 8 (ii) Correctly calculates to 2 4 sf Number of moles of anhydrous MgSO 4 = (i) / 7 (iii) Working / expression for M r and answer of the correct magnitude given to 2 4 sf M r = mass of residue / (ii) (iv) Correctly calculates relative atomic mass: A r = (iii) 96. [4] (c) (i) Reheat solid / residue to constant mass. (ii) To prevent absorption of water (vapour) [2] Qn 2 Total [9] Cambridge International Examinations 205

42 Page 6 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total FB 5 is MgCl 2 (aq); FB 6 is Zn(NO 3 ) 2 (s) 3 (a) Two reagents needed sodium hydroxide barium chloride / barium nitrate Observations: NaOH white precipitate, insoluble in excess Barium ions no precipitate / no change / no reaction Conclusions: Mg 2+ / magnesium (ion) is present and SO 4 2 / sulfate (ion) is not present (b) (i) Heating FB 6: look for the following nine observations (on gentle heating) solid melts / dissolves / turns to liquid / solution liquid is colourless bubbling / fizzing / effervescence / boiling steam / (water) vapour given off / misty fumes/ condensation formed (when strongly heated), brown gas / fumes yellow solid / residue formed (gas) relights a glowing splint gas turns (blue) litmus red (ignore bleaching) white / cream / paler (yellow) solid / residue Award marks as shown. 5 observations correct = 4 marks 4 observations correct = 3 marks 3 observations correct = 2 marks 2 observations correct = mark 4 [4] Cambridge International Examinations 205

43 Page 7 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total (ii) Observations with AgNO 3 and H 2 SO 4 No reaction / no change in both With NH 3 white precipitate soluble in excess With cold NaOH white precipitate soluble in excess With hot NaOH no reaction / no gas produced / (gas) did not turn red litmus blue With NaOH + Al (gas) turns (damp red) litmus blue (iii) Identification FB 6 is Zn(NO 3 ) 2 [0] Qn 3 Total [4] Cambridge International Examinations 205

44 CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 205 series 970 CHEMISTRY 970/35 Paper 3 (Advanced Practical Skills ), maximum raw mark 40 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners meeting before marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the October/November 205 series for most Cambridge IGCSE, Cambridge International A and AS Level components and some Cambridge O Level components. IGCSE is the registered trademark of Cambridge International Examinations.

45 Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total (a) I Initial and final readings and titre value given for rough titre and initial and final readings for two (or more) accurate titrations (minimum of 2 2 box) II Titre values recorded for accurate titrations and Appropriate headings for the accurate titration table and cm 3 units. initial / start burette reading / volume / value final / end burette reading / volume / value (not amount) titre or volume / FA 4 and used / added unit: / cm 3 or (cm 3 ) or in cm 3 (for each heading) III All accurate burette readings are to the nearest 0.05 cm 3. Do not award this mark if: 50(.00) is used as an initial burette reading more than one final burette reading is 50.(00) any burette reading is greater than 50.(00) there is only one accurate titration. IV There are two uncorrected accurate titres within 0.0 cm 3 Do not award this mark if, having performed two titres within 0.0 cm 3, a further titration is performed which is more than 0.0 cm 3 from the closer of the initial two titres, unless a further titration, within 0.0 cm 3 of any other, has also been carried out. Do not award the mark if any accurate burette readings (apart from initial 0 cm 3 ) are given to zero dp Examiner rounds any burette readings to the nearest 0.05 cm 3, checks subtractions and then selects the best titres using the hierarchy: two (or more) accurate identical titres, then two (or more) accurate titres within 0.05 cm 3, then two (or more) accurate titres within 0.0 cm 3, etc These best titres are used to calculate the mean titre, expressed to nearest 0.0 cm 3. 3 Examiner calculates the difference (δ) between the mean titres obtained by the candidate and the Supervisor. Accuracy marks are awarded as shown. Award V, VI and VII if δ 0.20 (cm 3 ) Award V and VI if 0.20 < δ 0.30 Award V, only, if 0.30 < δ 0.50 [7] Spread penalty: if the two best (corrected) titres used by the Examiner were 0.50 cm 3 apart, cancel one accuracy mark. Cambridge International Examinations 205

46 Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total (b) Candidate must take the average of two (or more) titres that are within a total spread of not more than 0.20 cm 3. Working / explanation must be shown or ticks must be put next to the two (or more) accurate readings selected. The mean should be quoted to 2 dp, and be rounded to nearest 0.0 cm 3. Two special cases, where the mean need not be to 2 dp: Allow mean expressed to 3 dp only for or (e.g cm 3 ) Allow mean if expressed to dp, if all accurate burette readings were given to dp and the mean is exactly correct. (e.g and 26.2 = 26. is allowed) (e.g and 26. = 26. is wrong should be 26.05) Note: the candidate s mean will sometimes be marked correct even if it was different from the mean calculated by the Examiner for the purpose of assessing accuracy. (c)(i)(ii) Correctly calculates n(thio) = 0.0 (b) / 000 n(i 2 ) = 0.5 (i) Both answers must be given to 3 or 4 significant figures (iii) (iv) Correctly calculates n(kmno 4 ) = = or or Correct expression, with answer given to 2, 3 or 4 sig fig n(i 2 ) = (ii) / (iii) 2 Theoretical answer = 5.0 (for 2.0 mol KMnO 4 ) (v) Correct equation ticked, corresponding to (iv) (vi) Allow any one of the following answers: An iodide ion loses one electron 2I 2e I 2 (ionic equation must be correctly balanced) Oxidation number of iodine increases from / (in iodide ion) to 0 (in iodine) [5] (d) (i) % error = 0.06 / = 0.24 % (ii) The student is wrong, since KI / FA 3 is in excess. [2] Qn [Total: 5] 2 (a) I Table for readings, headings and correct units: Headings: volume of FA 5 / acid (volume of water if included must be correct) Time Units allow Vol or / cm 3 etc. Cambridge International Examinations 205

47 Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total II Three reaction times all recorded to nearest second III and IV Examiner to calculate the time differences between Expt and Expt 2 (t 2 t ). Then calculate 0% of the time for Expt to dp (x). If (t 2 t ).> x award III. Examiner to calculate the time differences between Expt 2 and Expt 3 (t 3 t 2 ). Then calculate 20% of the time for Expt 2 to dp (y). If (t 3 t 2 ).> y award IV. (b) (i) Rates correctly calculated All answers expressed to same sig fig (but not sf) Unit given... / s or (s ) 2 [4] (ii) Correctly calculates Expt, conc = (or or 0.086) mol dm 3 and Expt 3, conc = (or or 0.029) mol dm 3 Both answers must be given to 2, 3 or 4 sig figs (iii) Rate increases with (increase of) concentration (iv) Time is shorter for sulfuric acid Sulfuric acid has a greater / doubled concentration of H + ions. (v) time (for reaction) will be greater less depth (of solution) in the 250 cm 3 [5] Qn 2 [Total: 9] FA 6 is Na 2 SO 3 ; FA 7 is CaCl 2 ; FA 8 is MgSO 4 ; FA 9 is Al 2 (SO 4 ) 3 ; FA 0 is MnSO 4 3 (a) (i) Both observations required white precipitate with Ba 2+ ion Precipitate dissolves / partially dissolves in (excess) HCl (ii) Both observations required white precipitate with Ba 2+ ion precipitate insoluble / no change with HCl (iii) When heated, gas produced decolourises KMnO 4 paper. (iv) No change (when NaOH added) / no ppt / no reaction and green (solution) formed when KMnO 4 added Colourless solution(with acid) Cambridge International Examinations 205

48 Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level October/November Question Indicative material Mark Total (v) Anion is sulfite and one piece of evidence FA 6 with acid SO 2 / gas which decolourises KMnO 4 is formed or FA 6 with Ba 2+ white precipitate / BaSO 3 formed which dissolves in acid / partially soluble in acid (vi) Na 2 SO 3 + H 2 O 2 Na 2 SO 4 + H 2 O [7] (b) (i) FA 7 FA 8 FA 9 FA 0 NaOH white ppt white ppt white ppt off-white / buff / beige / light brown ppt excess NaOH NH 3 excess NH 3 no change or insoluble in excess no ppt or no reaction (ignore) no change or insoluble in excess (ppt) dissolves or soluble in excess insoluble in excess or ppt darkens (owtte) white ppt white ppt off-white / buff / beige / light brown ppt no change or insoluble in excess no change or insoluble in excess insoluble in excess or ppt darkens (owtte) 5 (ii) Conclusions FA 7 calcium / Ca 2+ or barium/ba 2+ FA 8 magnesium / Mg 2+ FA 9 aluminium / Al 3+ FA 0 manganese(ii)/mn 2+ Four correct = 2 marks Two or three correct = mark (iii) M OH M(OH) 2 (for any divalent cation) or M OH M(OH) 3 (for any trivalent cation) 2 (iv) Use higher concentration [9] Qn 3 [Total: 6] Cambridge International Examinations 205