Home / iGCSE Chemistry (0620) Theory (Core):9.5 Corrosion of metals: Exam Style Questions Paper 3

iGCSE Chemistry (0620) Theory (Core):9.5 Corrosion of metals: Exam Style Questions Paper 3- New Syllabus

iGCSE Chemistry Theory (Core) Paper 3 - All Chapters

Question

This question is about metals.
(a) Iron is extracted from its ore using carbon in a blast furnace.
Aluminium is extracted from its ore using electrolysis.
(i) Name the main ore of aluminium.
(ii) Explain why aluminium is not extracted from its ore by reduction with carbon.
Give your answer in terms of the reactivity series.
(iii) An equation for the reduction of iron(III) oxide using carbon is shown.
\(2\text{Fe}_2\text{O}_3 + 3\text{C} \rightarrow 4\text{Fe} + 3\text{CO}_2\)
Explain how this equation shows that iron(III) oxide is reduced.
(b) Iron is made into stainless steel. Stainless steel is an alloy that resists rusting.
(i) State what is meant by the term alloy.
(ii) Name the two substances required for iron to rust. 
(iii) State the chemical name for rust.
(c) Table 6.1 shows the observations when four different metals are added separately to dilute hydrochloric acid.
(i) Put the four metals in order of their reactivity. Put the least reactive metal first.
(ii) Complete the word equation for the reaction of strontium with hydrochloric acid.

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• Topic 9.6 — Extraction of metals (Part a)
• Topic 9.3 — Alloys and their properties (Part b(i))
• Topic 9.5 — Corrosion of metals (Parts b(ii), b(iii))
• Topic 9.4 — Reactivity series (Part c)

▶️ Answer/Explanation

(a)(i) For the correct answer:
bauxite

Explanation: The main ore of aluminium is bauxite, which contains aluminium oxide (\(\text{Al}_2\text{O}_3\)). Aluminium is extracted from purified bauxite by electrolysis.

(a)(ii) For the correct answer:
aluminium is more reactive (than carbon in the reactivity series)

Explanation: In the reactivity series, carbon can only reduce the oxides of metals that are less reactive than itself. Aluminium is placed above carbon in the reactivity series, so carbon cannot displace it from its oxide. Electrolysis must be used instead.

(a)(iii) For the correct answer:
the iron(III) oxide has lost oxygen (atom(s))

Explanation: In the IGCSE Core syllabus, reduction is defined as the loss of oxygen. In this reaction, \(\text{Fe}_2\text{O}_3\) loses its oxygen atoms to form Fe, so it has been reduced. (Carbon simultaneously gains oxygen and is oxidized.)

(b)(i) For the correct answers:
mixture
of a metal with other elements

Explanation: An alloy is defined as a mixture of a metal with one or more other elements. For example, stainless steel is an alloy of iron with chromium, nickel, and carbon.

(b)(ii) For the correct answers:
water
oxygen

Explanation: Both water and oxygen are essential for the rusting of iron. Rust is formed via an electrochemical process requiring the presence of both substances.

(b)(iii) For the correct answers:
hydrated
iron(III) oxide

Explanation: The chemical name for rust is hydrated iron(III) oxide, reflecting that it is iron(III) oxide (\(\text{Fe}_2\text{O}_3\)) chemically combined with water molecules.

(c)(i) For the correct answer:
Nb → Fe → Mn → Sr (least reactive first)

Explanation: The reactivity can be deduced from the observations in Table 6.1. Nb shows no reaction, Fe shows a very slow reaction with few bubbles, Mn gives off bubbles quickly, and Sr produces many bubbles very quickly with a rapid temperature increase. Therefore, reactivity order (least to most) is: Nb, Fe, Mn, Sr.

(c)(ii) For the correct answers:
strontium + hydrochloric acid → strontium chloride + hydrogen

Explanation: When a reactive metal reacts with dilute hydrochloric acid, the products are always a metal chloride salt and hydrogen gas. Strontium chloride and hydrogen are the correct products.

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