Chemistry · May / June 2025 · Paper 61 · Question 2
0620
As printed in the paper
The question as text
A student investigates how the rate of reaction of magnesium ribbon with dilute acid changes as the concentration of the acid is changed. The student uses five solutions of the same acid, A, B, C, D, and E. Each solution has a different concentration. The acid is in excess in all experiments. The student does five experiments. Experiment 1 • Use a 50 cm3 measuring cylinder to pour 30 cm3 of acid A into a 100 cm3 conical flask. • Add a coil of magnesium ribbon to the acid in the conical flask and immediately start a stop- watch. • Continually swirl the mixture in the conical flask until the magnesium ribbon disappears completely. Immediately stop the stop-watch and record the time in seconds to the nearest second. • Empty and rinse the conical flask with distilled water. Experiment 2 • Repeat Experiment 1 using 30 cm3 of acid B instead of acid A. Experiment 3 • Repeat Experiment 1 using 30 cm3 of acid C instead of acid A. Experiment 4 • Repeat Experiment 1 using 30 cm3 of acid D instead of acid A. Experiment 5 • Repeat Experiment 1 using 30 cm3 of acid E instead of acid A.
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2(a)[2]
M1 times are correct for all five experiments (20, 25, 42, 56, 95)
M2 All times recorded in whole numbers of seconds only
2(b)[4]
M1 y-axis scale is linear and points take up over half of space available
M2 and M3 All points plotted correctly
M4 best fit line
2(c)[2]
M1 correct working shown at a concentration of 1.3 on graph
M2 correct reading from their working shown on graph
2(d)(i)[2]
M1 0.25
M2 cm / s
2(d)(ii)[1]
Experiment 5
2(e)[1]
to check / verify / compare results / to get concordant results /
2(f)(i)[2]
M1 both temperatures are correct (24.0, 46.5)
M2 temperature change calculated correctly (22.5) and all temperatures and temperature change given to one dp
2(f)(ii)[1]
a change of temperature will change the rate of reaction
2(f)(iii)[1]
the polystyrene would prevent heat escaping
2(f)(iv)[1]
use a water bath (at room temperature / at starting temperature)
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