VS 2023 O Level Pure Chemistry P3 Answer Scheme

1 Victoria School2023 O Level ChemistrySuggested Answer to Chemistry Paper 3QnSkillAnswerMark1(a)(i)PDO MMO Results table:experimentvolume of A / cm3volume of B / cm3volume of deionized water / cm3reaction time / srate of reaction / s-111.010.00.02934.521.02.08.02733.6631.04.06.09310.841.06.04.05418.551.08.02.03826.31m- volume of B must be 4.0, 6.0 and 8.0 cm31m- total volume of water and B = 10cm31m-volume of water and B and time given to the correct s.f1m- accuracy for first reading 1m- trend between volume of B and time 51(a)(ii)MMOSee table aboveAll values calculated correctlyAll values to three significant figures111(b)(i)ACErate of reaction / s-1 volume of B / cm3

2 1m-Scale chosen is appropriate- no awkward scale(no 3, 8, 1.5, 6, 7, etc) (uniform scale chosen to use more than half of each axis)1m- graph of best fit - equal distribution of points. -To draw curve if it looks like one- (only 1 anomalous point allowed)line must pass through originpoints not on the line must be balanced on either side and any anomalous points ignored) *1m-Axes (include labels with units)1m all Points plotted correctly (to half a small square) 11111(b)(ii)ACEvolume of B / cm3 rate of reaction / s-1 Correct volume of B read from graph with units shown (5.25 cm3 ± 0.10). Working on the graph111(c)(i)ACEMethod 1: conc. of B = 10/11 x 0.1 = 0.0909 mol/dm3OrMethod 2Concentration of B: 0.1 mol/dm3 Volume: 10 cm3No. of moles of B: 0.1 x 10/1000 = 0.001 molVolume of reaction mixture: 10+1= 11cm3Concentration of B = 0.001 = 0.0909 mol/dm3 (11/1000) 1

3 1(c)(ii)ACEPDOConcentration of B = 0.09091 mol/dm3 / 5 = 0.0182 mol/dm3appropriate units in final answers in (c)(i), (ii) (mol/dm3)Rejected answer: concentration of B = 2/11 x 0.1 = 0.0182 as question asked for deduction. So students have to use the answer from ci.111(c)(iii)The rate of reaction increases as the volume of B added increases. If Line graph: graph shows a straight line and has a constant gradientIf Curve: graph shows a curve with an increasing gradient. 1mAs the concentration of B increases, there are more reacting particles per unit volume.Hence there are more effective collisions between reacting particles resulting in a higher rate of reaction. 111(c)(iv)To dilute the sodium thiosulfate solution and ensure that the total volume of reaction mixture remains the same to ensure a fair experiment. 1mVolume of B is proportional to its concentration of B 1m111(d)(i)ACEpercentage uncertainty = 0.2 ÷ 10 x 100 = 2.0%appropriate significant figures in final answers in (d) (i)111(d)(ii)PDOUse a burette to measure volume of B instead of a measuring cylinderOrUse of a light sensor with a data logger to measure reaction time1Total: 27

4 QnSkillAnswerMark2(a)(i)MMOtestobservationsTest 1Remove the stopper from a sample of C in a test tube. Heat the sample in the test tube gently at first then strongly for 1 minute.Green solid turned black on heatingColourless liquid form