Corrosion and extraction of metals — GCSE Chemistry practice questions

Question 1

A gardener leaves a steel spade outside the shed all winter and it turns orange-brown.

Which two substances must both be present for the spade to rust?

Accepted Answer

C: oxygen and water. Iron and steel rust only when both water and oxygen are present. The product is hydrated iron(III) oxide. Salt speeds rusting up but is not needed, and carbon dioxide and nitrogen are not involved.

Question 2

A steel gas pipe is buried in damp soil. An engineer connects blocks of another metal to the pipe to protect it from rusting.

Which metal and reason are correct?

Accepted Answer

C: magnesium, because it is more reactive than iron, so it loses electrons instead of the iron. Magnesium is more reactive than iron, so it is oxidised (loses electrons) in place of the iron and the pipe does not rust. Copper is less reactive and would not protect the iron. Sodium reacts rapidly with the water in the damp soil, so it would be used up at once.

Question 3

In the blast furnace some substances are formed in one reaction and then used up in another.

Which list contains ONLY substances that are both formed and used up inside the furnace?

Accepted Answer

A: calcium oxide, carbon dioxide, carbon monoxide. Carbon dioxide is formed when coke burns (and from limestone) and is used when it reacts with more coke. Carbon monoxide is formed from that reaction and used to reduce the iron(III) oxide. Calcium oxide is formed from limestone and used to remove silicon(IV) oxide.