O-LevelChemistryRates of Reaction5070/21 · Oct/Nov 2018 · Q910 Marks

Cerium is a metal with a relative atomic mass of 140. Cerium powder reacts with sulfuric acid. 2Ce(s) + 3H2SO4(aq) → Ce2(SO4)3(aq) + 3H2(g)

(a)Describe and explain, using ideas about collisions between particles, how the rate of this reaction changes when the concentration of sulfuric acid is decreased. All other conditions stay the same.[2]
(b)Describe and explain how the rate of this reaction changes when large pieces of cerium are used instead of cerium powder. All other conditions stay the same.[1]
(c)The reaction of cerium with sulfuric acid is exothermic. Complete the energy profile diagram to show the enthalpy change for this reaction. [Figure showing energy profile diagram with y-axis 'energy' and x-axis 'progress of reaction'][2]
(d)Calculate the maximum volume of hydrogen, in dm³, formed when 12.6g of cerium reacts with excess sulfuric acid at room temperature and pressure. [Ar: Ce, 140] volume .............................................................. dm³[3]
(e)The formula of cerium carbonate is Ce2(CO3)3 Calculate the percentage by mass of cerium in cerium carbonate. .............................................................. %[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2018). The mark or mark type is shown in brackets.

[2] rate of reaction decreases (no mark) fewer particles per unit volume / fewer particles per cm³ / particles further apart/less concentrated particles (1) collision frequency decreases / fewer particles collide per second (1)
[1] rate of reaction decreases (no mark) pieces have smaller surface area exposed / powder has larger surface area exposed / more particles (on surface) exposed to acid (1)
[2] reactants next to the left line and products next to the right line and reactant level above product level (1) arrow downwards between reactants and products (1)
[3] mol Ce = 0.09 (1) mol H2 = 0.135 (1) volume of H2 = 3.24 (dm³) (1)
[2] relative formula mass = 460 (1) percentage = 60.9% / 61% (1)

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