O-LevelChemistryMetals & Reactivity5070/22 · May/June 2020 · Q49 Marks

Part of the reactivity series is shown. magnesium aluminium zinc chromium iron more reactive less reactive

(a)Predict the names of the products formed when chromium reacts with dilute hydrochloric acid.[1]
(b)Powdered zinc is added to aqueous chromium(III) ions, Cr3+(aq). Construct an ionic equation, with state symbols, for this reaction.[2]
(c)Explain why aluminium does not react with water.[2]
(d)Hydrogen peroxide, an oxidising agent, is added to aqueous potassium iodide in a test-tube. Describe the colour change seen in the test-tube.[1]
(e)(i)Chromium is extracted by the reaction of aluminium with chromium(III) oxide, Cr2O3. Write the equation for this reaction.[1]
(e)(ii)Suggest a compound that can reduce chromium(III) oxide to chromium metal.[1]
(f)State one advantage of recycling metals.[1]

Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

[1] 4(a) reacts to give hydrogen and chromium chloride (1)
[1] 4(b) balanced equation 3Zn + 2Cr3+ → 3Zn2+ + 2Cr (1)
[1] 4(b) correct state symbols dependent on correct symbols and formulae (1)
[1] 4(c) aluminium has an oxide layer / aluminium oxide on the surface (1)
[1] 4(c) this layer is impermeable to water / layer is non-porous / layer is protective barrier against water (1)
[1] 4(d) colourless to brown (1)
[1] 4(e)(i) 2Al + Cr2O3 → Al2O3 + 2Cr (1)
[1] 4(e)(ii) carbon monoxide / CO (1)
[1] 4(f) saves natural resources / less environmental damage due to mining / saves energy (1)

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