O-LevelChemistryRates of Reaction5070/22 · Oct/Nov 2019 · Q413 Marks

The equation shows the reaction of calcium carbonate with hydrochloric acid. CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)

(a)The rate of this reaction can be determined by measuring the decrease in mass of the reaction mixture. Describe one other method of following the progress of this reaction.[2]
(b)Describe and explain, using ideas about collisions between particles, how the rate of reaction changes when the same mass of calcium carbonate is used in smaller pieces. All other conditions stay the same.[2]
(c)Describe and explain, using ideas about collisions between particles, how the rate of reaction changes when the temperature is increased. All other conditions stay the same.[3]
(d)Calculate the minimum mass of calcium carbonate, in grams, needed to produce 16.8 cm³ of carbon dioxide at room temperature and pressure. Give your answer to three significant figures. mass of calcium carbonate ..................................................................... g[2]
(e)Describe a test for carbon dioxide. test observation[2]
(f)Calcium hydroxide can be used to control the pH of the soil. Explain how calcium hydroxide controls the pH of the soil.[2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.

[1] measuring the volume of gas
[1] at known time intervals
[0] rate faster (no mark by itself)
[1] greater number of particles exposed
[1] increased collision frequency / more collisions per second
[0] rate faster (no mark by itself)
[1] particles move faster / particles have more kinetic energy
[1] greater number of particles have energy above (or equal to) the activation energy / more successful collisions
[1] increased collision frequency / more collisions per second
[1] mol CO2 = 16.8 / 24000 OR 7 × 10⁻⁴ OR 0.0007
[1] mass of CaCO3 = 7 × 10⁻⁴ × 100 = 0.0700 (g)
[1] lime water
[1] turns milky / turns cloudy
[1] calcium hydroxide alkaline / calcium hydroxide basic
[1] neutralises acids / neutralises the soil / raises pH of soil / makes soil less acidic

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