9701 CHEMISTRY. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers.

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Emmeline Turner
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1 CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary Advanced Level MARK SCHEME f the March 206 series 970 CHEMISTRY 970/33 Paper 3 (Advanced Practical Skills), maximum raw mark 40 This mark scheme is published as an aid to teachers cidates, 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 befe marking began, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper the Principal Examiner Rept f Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes f the March 206 series f most Cambridge IGCSE Cambridge International A AS Level components. IGCSE is the registered trademark of Cambridge International Examinations.

2 Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level March (a) I All thermometer readings mass of FA 2 recded. Do not award if mass of FA 2 > 0.50 g. [4] II All temperatures recded to 0.5 C. Award III IV if within ranges given of supervis s value. 2 supervis s T / C III IV 46.0 ± 5.0 ± ± 4.0 ± ± 3.0 ± ± 2.0 ± ±.0 ± 0.5 < 6.0 ± 0.5 I Axes labelled with units unifm scale chosen to use me than half of each axis including 0 C above the highest recded temperature. [4] II All recded points plotted (minimum 9). III Appropriate lines of best fit drawn: best fit lines must be a smooth curve; Points not on the line must be balanced on either side of the bestfit line any points ringed labelled as anomalous igned. IV Lines extrapolated crect value (within 0.5 C) of T read from graph. (c) (i) Crectly calculates Q = T from. [3] (ii) Crect expression f value of enthalpy change (c)(i) 24.3 = (igne sign) mass in (a) 000 Negative sign both answers recded to 2 4 sig. fig. no rounding to sig. fig. during calculation (unless exact value). (d) Increct, as the acid was in excess already. [] (e) Any one from: use lid use specified extra insulation to reduce heat losses (by convection conduction); use a pipette burette f FA to reduce % err / as me accurately calibrated (owtte); use magnesium turnings / powder so reaction complete sooner as there is heat loss while magnesium ribbon is still reacting; use lid plastic cup with higher walls to reduce acid spray; [] Cambridge International Examinations 206

3 Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level March (a) I Initial final burette readings volume added recded f rough titre accurate titre details tabulated. II Initial final burette readings recded volume of FA 4 added recded f each accurate titration. All headings units crect f accurate titrations: initial / final (burette) reading / volume reading / volume at start / finish volume / FA 4 added / used titre (cm 3 ) / cm 3 in cm 3 cm 3 by every entry. [7] III All accurate burette readings are recded to the nearest 0.05 cm 3. IV Has two uncrected, accurate titres within 0. cm 3. V, VI VII Award V, VI VII f δ 0.20 cm 3 Award V VI f 0.20 cm 3 < δ 0.30 cm 3 Award V f 0.30 cm 3 < δ 0.50 cm 3 Mean titre crectly calculated from clearly selected values. Cidates must average two ( me) titres where the total spread is 0.20 cm 3. Wking must be shown ticks must be put next to the two ( me) accurate readings selected. The mean should nmally be quoted to 2 d.p. rounded to the nearest 0.0. Note: the cidate s mean will sometimes be marked as crect even if it is different from the mean calculated by the examiner f the purpose of assessing accuracy. [] (c)(i)(ii) Crectly calculates (ii) = (i) [5] (iii) (iv) Crect expression (c)(ii) mol Mg = mass in (a) / 24.3 mol HCl = (c)(iii) 25 / 000 mol HCl > 2 mol Mg (owtte) so the statement is crect. Allow ecf from increct (iii). Final answers (i), (ii) (iii) to 3 4 sig. fig. no rounding errs. Cambridge International Examinations 206

4 Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level March (d) Crect expression answer to minimum 2 sig. fig. / crect answer to minimum 2 sig.fig. FA 3 (is measured me accurately). Allow ecf from > 4.67 cm 3 then FA 4 (is measured me accurately). [] test observations FA 5 FA 6 NaOH no reaction / no change / no ppt white ppt, soluble in excess NH 3 no reaction / no change / no ppt white ppt, insoluble in excess HCl (warm) H + / MnO 4 blue solution brown gas / gas turning brown / gas turns blue litmus red / bleaches decolourises / purple to colourless (solution) stays colourless no reaction / no change stays purple / pink changes to purple / pink Ba 2+ / HCl no reaction / no change / no ppt white ppt, insoluble in HCl FA 5 is NaNO 2 ; FA 6 is Al 2 (SO 4 ) 3 ; FA 7 is Na 2 SO 3 (Na 2 S 2 O 5 ) 3 (a) Observations fully crect f both FA 5 FA6 f NaOH. [8] Observations fully crect f both FA 5 FA6 f NH 3. Observation of blue solution brown gas with FA 5 no reaction with FA 6 f HCl. Observations fully crect f both FA 5 FA6 f H + / MnO 4. Observations fully crect f both FA 5 FA6 f Ba 2+ / HCl. Cations: FA 5 unknown FA 6 Al 3+ / aluminium Anions: FA 5 NO 2 / nitrite FA 6 SO 4 2 / sulfate Cambridge International Examinations 206

5 Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level March (i) (Warm with) Al NaOH test gas with (damp) red litmus paper. [5] No reaction not nitrate / N / same element as FA 5. (ii) BaCl 2 / Ba(NO 3 ) 2 HCl / HNO 3 H + / KMnO 4 / acidified potassium manganate(vii) any named acid, (warm) test gas with H + / KMnO 4. Ba 2+ acid: white ppt, soluble in acid H + / MnO 4 : solution decolourises / purple to colourless acid test gas with H + / KMnO 4 : gas (evolved with acid) which decolourises H + / MnO 4 (paper). FA 7 contains sulfite / SO 3 2 Cambridge International Examinations 206

MARK SCHEME for the October/November 2015 series 9701 CHEMISTRY

MARK SCHEME for the October/November 2015 series 9701 CHEMISTRY CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME f the October/November 205 series 970 CHEMISTRY 970/35 Paper 3 (Advanced Practical Skills