O-LevelChemistryElectrolysis5070/22 · Oct/Nov 2021 · Q910 Marks
This question is about sulfuric acid and sulfates.
- (a)(i)Sulfur is one of the raw materials used in the Contact process to make sulfuric acid. Name two other raw materials used to make sulfuric acid.[1]
- (a)(ii)Name the catalyst used in the Contact process.[1]
- (b)(i)The electrolysis of dilute sulfuric acid using inert electrodes produces oxygen at the anode. Define the term electrolysis.[2]
- (b)(ii)Construct the equation for the reaction taking place at the cathode.[1]
- (c)Dilute sulfuric acid reacts with sodium hydroxide. H2SO4 + 2NaOH → Na2SO4 + 2H2O A student adds 0.76g of solid sodium hydroxide to 45 cm³ of 0.20mol/dm³ sulfuric acid. Show by calculation that the sodium hydroxide is in excess.[3]
- (d)Aqueous sodium hydroxide is warmed with ammonium sulfate. State the names of the three products formed in this reaction. 1 2 3[2]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.
- [1] air AND water
- [1] vanadium(V) oxide
- [2] decomposition of an ionic compound / decomposition of an electrolyte (1)
- using electricity (1)
- [1] 2H+ + 2e- → H2
- [3] mol H2SO4 = 45 / 1000 × 0.20 OR 0.009 (1)
- mol sodium hydroxide = 0.76 / 40 OR 0.019 mol (1)
- (sodium hydroxide because 0.019 is greater than) 2 × 0.009
- OR
- (sodium hydroxide because 0.009 is less than) 0.019/2 (1)
- [2] ammonia AND sodium sulfate AND water (2)
- if 2 marks not scored 1 mark for any two of
- ammonia, sodium sulfate or water
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