The manager of a water treatment plant stores dilute hydrochloric acid in a tank. A new student suggests making the tank from sodium because sodium is a met...
Question 1 Report
The manager of a water treatment plant stores dilute hydrochloric acid in a tank. A new student suggests making the tank from sodium because sodium is a metal. The manager rejects the suggestion after considering the reaction of sodium with water.
(a) Describe what would happen if sodium were put into water. [1]
(b) Give one more suitable material for the tank. [1]
This bridge is protected by sacrificial blocks of zinc attached to its underwater steel piles. Fig. 1 shows a zinc block bolted to a steel pile in seawater. The zinc block is replaced once much of it has reacted. The method is also used on the steel hull of some ships.
(a) Give the name of this method of protecting steel. [1]
(b) Describe why zinc reacts instead of the iron in the steel pile. [2]
(c) Give one metal, other than zinc, that could act as a sacrificial metal for iron. [1]
(d) Give one reason why copper would not be suitable as the sacrificial metal. [1]
Answer Details
Labelled answer diagram:
(a) Sodium reacts vigorously with water. It may move on the surface and produces hydrogen; the hydrogen or sodium may burn. [1]
(b) A suitable tank material is plastic, glass, or a suitable corrosion-resistant lined steel tank. [1]
(a) The protection method is sacrificial protection, also called a sacrificial anode. [1]
(b) Zinc is more reactive than iron, so zinc oxidises and loses electrons in preference to the iron in the steel pile. The zinc is used up instead of the iron. [2]
(c) Magnesium or aluminium could act as a sacrificial metal for iron. [1]
(d) Copper is less reactive than iron, so it would not oxidise in preference to iron and cannot provide sacrificial protection. [1]
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