Question 1:
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
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
Question 2:
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.
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.