O-LevelChemistryRates of Reaction5070/22 · May/June 2016 · Q47 Marks

Sulfuric acid is manufactured by the contact process.

(a)State the conditions used in the contact process. temperature ................................................................................................................. pressure .................................................................................................................... catalyst ......................................................................................................................[2]
(b)In the contact process, sulfur dioxide reacts with oxygen. 2SO2(g) + O2(g) ⇔ 2SO3(g) Describe and explain the effect of increasing the concentration of oxygen on the rate of this reaction.[2]
(c)The catalyst used in the contact process increases the rate of the reaction. Describe one other advantage of using a catalyst in an industrial process.[1]
(d)Sulfuric acid is used to make the fertiliser potassium sulfate, K2SO4. Calculate the percentage by mass of potassium in this fertiliser.[2]

Mark scheme

Marking points from the official mark scheme (May/June 2016). The mark or mark type is shown in brackets.

[1] Temperature 350 to 500 °C
[1] Pressure 1 to 10 atmospheres
[1] Catalyst vanadium(V) oxide/vanadium pentoxide/V2O5
[1] Rate of reaction increases AND particles closer together/more particles per unit volume/more crowded particles
[1] More collisions per second/increased collision frequency/particles collide more often
[1] Reduces the cost of the process/(allows reactions to be carried out at) lower temperatures/(allows reactions to be carried out at) lower pressures
[1] Relative formula mass = 174
[1] Percentage of K = 44.8%

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