Chemistry · May / June 2024 · Paper 61 · Question 2

0620

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The question as text

A student investigates the temperature change when magnesium reacts with dilute sulfuric acid. The student does five experiments. Experiment 1 ● Use a 25 cm3 measuring cylinder to pour 20 cm3 of dilute sulfuric acid into a boiling tube. ● Use a thermometer to measure the initial temperature of the acid in the boiling tube. Record the initial temperature. ● Add a coiled 5 cm length of magnesium ribbon to the acid in the boiling tube. At the same time start a timer. ● Continually stir the contents of the boiling tube using the thermometer. ● After 45 seconds, measure the temperature of the mixture in the boiling tube. Record this temperature. ● Rinse the boiling tube with distilled water. Experiment 2 ● Use the 25 cm3 measuring cylinder to pour 20 cm3 of dilute sulfuric acid into the boiling tube. ● Use a 10 cm3 measuring cylinder to add 2.0 cm3 of distilled water to the acid in the boiling tube. ● Place a bung in the boiling tube and invert the tube to mix the acid and water. ● Use the thermometer to measure the initial temperature of the contents of the boiling tube. Record the initial temperature. ● Add a coiled 5 cm length of magnesium ribbon to the contents of the boiling tube. At the same time start a timer. ● Continually stir the contents of the boiling tube using the thermometer. ● After 45 seconds, measure the temperature of the mixture. Record this temperature. ● Rinse the boiling tube with distilled water. Experiment 3 ● Repeat Experiment 2, adding 4.0 cm3 of distilled water instead of 2.0 cm3. Experiment 4 ● Repeat Experiment 2, adding 6.0 cm3 of distilled water instead of 2.0 cm3. Experiment 5 ● Repeat Experiment 2, adding 10.0 cm3 of distilled water instead of 2.0 cm3.

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2(a)[5]
M1 all five volumes of dilute sulfuric acid are 20
M2 all five volumes of water are correct (0, 2, 4, 6, 10)
M3 all temperatures and temperature changes are recorded to nearest 0.5 °C
M4 all five temperatures after 45 seconds are recorded correctly (37.0, 34.0, 31.5, 30.0, 27.5)
M5 all temperature increases correct (12.0, 8.5, 6.0, 4.0, 1.5)
2(b)(i)[1]
5
2(b)(ii)[1]
larger / largest volume (being heated)
2(c)[4]
M1 suitable sensible scale on y-axis
M2 and M3 all five points plotted correctly
M4 best fit line
2(d)[2]
M1 correct working shown on graph
M2 correct value from their working to a point on the line
2(e)[2]
M1 (12 ÷ 45 =) 0.27 or 0.267 or 0.3
M2 °C / s
2(f)(i)[2]
any two from:
insulator
so reduces / prevents heat loss / traps heat
temperature (more) accurate / does not cool down / prevents temperature decreasing
2(f)(ii)[1]
volume used is not fixed / volume needed is not the same in each experiment / volume used is not 25 cm3
2(f)(iii)[1]
use a burette instead of a measuring cylinder
2(g)[1]
sketch line is below results line for all volumes of water

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