4 This question is about zinc and compounds of zinc.
A student produces pure crystals of zinc chloride by reacting zinc oxide with hydrochloric acid.
The equation for the reaction is:
ZnO(s) + 2 HCl(aq) → ZnCl2(aq) + H2O(l)
4-1 The student adds zinc oxide to hydrochloric acid until the zinc oxide is in excess
Give one observation that the student could make to show that the zinc oxide is in excess.
[1 mark]
ANSWER
Zinc oxide solid remaining may be observed
4-2 Why is excess zinc oxide used rather than excess hydrochloric acid?
[1 mark]
ANSWER
Excess zinc oxide can be filtered off.
4-3 Name one other compound that the student could add to hydrochloric acid to produce zinc chloride.
[1 mark]
ANSWER
Zinc hydroxide
4-4 Describe how the student should obtain crystals of zinc chloride from a solution of zinc chloride.
[2 marks]
ANSWER
Heat the solution in an evaporating basin to 3rystallization point and leave it to crystallize;
Pat dry with filter paper.
4-5 Zinc chloride is also produced in a displacement reaction between zinc and copper chloride solution.
The equation for the reaction is:
Complete the ionic equation for this reaction
[1 mark]
ANSWER
Zn + Cu2+ → Zn2+ + Cu
4-6 Why is zinc described as being 3xidized in this reaction?
[1 mark]
ANSWER
Zinc atoms loses (2) electrons s shown below
Zn → Zn2+ + 2e-
4-7 Zinc and copper can be used with another substance to produce electricity.
Complete Figure 7 to show how zinc, copper and another substance can be used to light a lamp.
Label:
• zinc
• copper
• the other substance used.
[3 marks]
ANSWER
Zinc electrode and copper electrode both inserted into solution (electrolyte) that would function as an electrochemical cell.
