(a) titration / volumetric analysis (b) C (5 cm 3 pipette) (c) M (before) yellow (d) M (after) - orange after adding 3.60 acid before adding acid.75 volume added 0.85 accept pink / red and combinations with orange Allow mark if correct colours reversed If readings are correct but in the wrong order, award mark for M and M 3 M 3.60 M.75 M3 0.85 M3 CQ on (M M) (e) (i).90.60.45.55 (ii) M (.60 +.45 +.55) 3 M.53 (cm 3 ) Correct final answer with no working scores () Accept.53 with 3 recurring If no results ticked in (i), then only use of two or three concordant titres can score in (ii) If only one result ticked, then no marks can be scored in (ii) Otherwise, both marks CQ on ticked results in (e)(i) Answer with zero as nd dp does not need trailing zero
Answers obtained by averaging other titre values do require answers to dp
a (i) M more accurate Accept more precise / gives an exact value (ii) M (thermal) insulator /poor conductor/keeps heat in/ reduces heat loss Accepts traps heat (iii) M stirring/mixing/swirling Ignore name of apparatus used (iv) M temperature goes down/stops rising/stays constant Accept measure ph/when ph = 7/when ph is less than 7 Reject changing to any ph value > 7 Accept use of any indicator (named example or just indicator) Ignore colour changes b M 9.4 M 3. M3 3.7 CQ on temperatures recorded Penalise negative sign Penalise second decimal place values, except zeroes, for M and M M and M both correct but wrong way around scores
c (i) M 9 points plotted correctly to nearest gridline Deduct for each error M If points not visible beneath line, assume them to be on line M3 straight line of best fit through first 5 points M4 straight line of best fit through last 4 points If lines do not cross or are joined by curve or straight line, only M3 or M4 can be awarded (ii) M volume of acid CQ on where lines cross Accept answer ± 0.5 to minimum of dp M maximum temperature CQ on where lines cross Accept answer ± 0. to minimum of dp Do not award either mark if lines do not intersect Apply dp penalty once only Award mark if both values correct but recorded in wrong places d M 55 ( 4. 5.5) M 70.5 Accept any value between 70 and 7 Accept 300 M CQ on M If vol used is 5, answer is 577.5 Accept any value between 577 and 578 accept 580 If vol used is 30, answer is 693 Accept 690 Ignore signs Correct final answer without working scores marks
e (i) M.5 0.05 M 0.0375 Correct final answer scores marks 37.5 scores M only (ii) M 800 0.0375 /800 answer to (e)(i) Accept correct use of.8 in place of 800 M 48 (kj/mol) M CQ on M provided 800 or.8 used correctly If 37.5 in (a)(i) then answer is 0.048 (kj/mol) Correct final answer scores marks Ignore answer in J/mol Ignore signs Total 9 marks
3 (a) M 3.60 M.5 M3.35 Award mark for both M and M correct but in wrong order Penalise missing zero in nd dp once only CQ on M and M 3 (b) (i) ticks in columns 3 and 4 (ii) M 3.50 + 3. 0 M 3.6(0) (cm 3 ) If no results ticked in (i), then only use of concordant titres can score in (ii) If only one result ticked, then no marks can be scored in (ii) Otherwise, both marks CQ on ticked results Answers with zero as nd dp do not need trailing zero Answers obtained by averaging other titre values do require nd dp Correct final answer with no working scores () (c) (i) M 0.07 5.0 000 M 0.0068 (mol) If no division by 000, only M can be scored Accept or more significant figures (ii) ( 0.0068 =) 0.00535 (mol) CQ on (c)(i) (iii) M 0.00535 0.085 M 0.34 (mol/dm 3 ) CQ on (c)(ii) Accept or more significant figures
3 (d) (i) white precipitate Ignore names and formulae Apply list principle for incorrect observations such as bubbles (ii) barium sulfate Accept BaSO 4 If both name and formula given, mark name only Total for Question 3 3
4 a M concentration Ignore from the same bottle M temperature / same temperature as acid Accept in either order Ignore references to volume b M 9.4 Award for both temperatures M 6.9 correct but in wrong order M3 (+).5 CQ on temperatures recorded Penalise negative sign c i cross in box D (The volume of acid used was 50.0 cm 3 instead of 5.0 cm 3 ) ii cross in box D (The alkali was added in 0.0 cm 3 portions but were recorded as 5.0 cm 3 portions) d M M M3 M4 Deduct for each error all points plotted correctly to nearest gridline If points not visible beneath line, assume them to be on the line straight line of best fit through first 4 points Lines must be drawn with a ruler straight line of best fit through last 3 points Penalise freehand once only ECF on incorrectly plotted points
If first line drawn to (3.6,0.0), do not award M3 If lines do not cross or are joined by curve or straight line, only one of M3 and M4 can be awarded
4 e M volume of alkali CQ on where lines cross Accept answer to nearest gridline to M maximum temperature CQ on where lines cross min dp Accept answer to nearest gridline to min dp Penalise missing dp once only If both values correct but in wrong order, award / 0/ if lines do not cross f i M M 0.650 0.05 0.065 / 0.063 6.5 scores / Accept 0.06 and 0.06 ii M 0.035 CQ on fi iii M M 0.035 000 CQ on fii 0.500 65 (cm 3 ) If M wrong because 000 missing, then award M by ECF Penalise failure to use 000 once only in i and iii Do not penalise rounding of intermediate answers and consequent final answer eg 65. If final answer obtained by use of V M = V M n n both marks may be awarded in iii T O T A L 8