O-LevelChemistryMetals & Reactivity5070/22 · May/June 2018 · Q27 Marks

The transition elements occupy the central block of the Periodic Table. Iron and copper are typical transition elements.

(a)The compounds of transition elements are often coloured. What is the colour of iron(III) hydroxide?[1]
(b)A redox reaction happens when iron filings are added to aqueous copper(II) sulfate. Fe(s) + Cu2+(aq) → Cu(s) + Fe2+(aq)
(b)(i)Describe what is observed during this reaction.[2]
(b)(ii)Use the equation to explain that oxidation takes place in this reaction.[1]
(b)(iii)Use the equation to explain that reduction takes place in this reaction.[1]
(c)Compounds containing ions of transition elements are often used as catalysts. Name a catalyst that is the compound of a transition element and state the reaction it catalyses. name reaction[1]
(d)Catalysts increase the rate of reaction by providing an alternative reaction pathway with a lower activation energy. Explain why catalysts are used in industry.[1]

Mark scheme

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

[1] 2(a) red-brown (1)
[2] 2(b)(i) Any two from: • solution turns from blue to (pale) green (1) • (iron filings get coated with) pink solid / pink deposit / pink coating (1) • temperature (of mixture) increases (1)
[1] 2(b)(ii) iron (atom) loses electrons (1)
[1] 2(b)(iii) copper ions gain electrons / copper(II) gains electrons (1)
[1] 2(c) transition metal oxide catalyst AND reaction (1) e.g. manganese(IV) oxide / manganese dioxide AND decomposition of hydrogen peroxide OR vanadium(V) oxide AND reaction of sulfur dioxide with oxygen / vanadium pentoxide AND formation of SO3 (from SO2)
[1] 2(d) low(er) temperatures needed / low(er) pressure needed / less heat needed / less energy needed / conserves energy resources / cheap(er) heating costs / cheap(er) fuel costs / cheap(er) pressure costs (1)

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