Figure 1.43 shows the observation of two experiments to study the effects of metals P and Q on rusting of iron.
(a) Suggest metals P and Q.
(b) Explain and include the half equations for the reactions in experiment I and experiment II.
(c) Arrange iron, metal P and metal Q in an ascending order of electropositivity.
Answer:
1. (a)
P : Copper
Q : Zinc
1. (b)
Experiment I
– Redox reactions.
– Iron undergoes oxidation reaction when iron atoms lose electrons to form Fe2+ ions.
Fe → Fe2+ + 2e−
– The blue spots in the test tube shows the presence of Fe2+ ions.
– Oxygen undergoes reduction reaction when oxygen gains electrons to form OH− ions.
O2 + 2H2O + 4e− → 4OH−
Experiment II
– Redox reactions.
– Zinc undergoes oxidation reaction when zinc atoms lose electrons to form Zn2+ ions.
Zn → Zn2+ + 2e−
– Oxygen undergoes reduction reaction when oxygen gains electrons to form OH− ions.
O2 + 2H2O + 4e− → 4OH−
– The pink spots in the test tube shows the presence of OH− ions.
– Absence of blue spots in the test tube indicates no Fe2+ ions.
1. (c) Cu, Fe, Zn
In the food manufacturing industry, steel plates are plated with tin before being used to make food cans. Explain how tin prevents steel from rusting.
Answer:
– Tin forms a protective oxide layer.
– The tin oxide layer protects the steel from coming into contact with oxygen and water. Therefore, steel does not oxidise and rusting does not occur.