Important Questions and Answers: Zinc

1. Write the action heat and cobalt nitrate on zinc oxide.

Ans: When zinc oxide is heated, it becomes yellow.
$$\ce{$\underset{\text{White}}{\ce{ZnO}}$->[\Delta] $\underset{\text{Yellow}}{\ce{Zn}}$}$$

2. When zinc oxide is heated with cobalt nitrate, a green colored mass is obtained known as Rinman’s green. The reaction involved is given below:

Ans: $$\ce{2Co(NO3)2->[\Delta]2CoO + 4NO2 + O2}$$
$$\ce{ZnO + CoO->[\Delta]$\underset{\text{Rinman’s green}}{\ce{ZnO.CoO}}$}$$

3. Why is zinc not considered as a transitional element?

Ans: Zinc is not called transitional element because:

  • Zinc has completely filled d-orbitals.
  • The compounds of zinc are colorless.
  • Zinc shows only one oxidation state.
  • It has low melting point.
  • It does not show catalytic activity.

4.  Why zinc can displace copper from copper sulphate solution?

Ans: Zinc can reduce copper from coppersulphate solution because the standard reduction potential of copper is very high than that of zinc. So, zinc get oxidizes itself to reduce copper as shown below.
$$\ce{Zn + CuSO4->ZnSO4 + Cu}$$

5. Name two ores of zinc with their molecular formula.

Ans: The two ores of zinc are as follows:
i. Zinc Blende (ZnS)
ii. Calamine (ZnCO3)

6. Why does zinc become moist and dull in air?

Ans: Zinc when introduced to moist air, forms a protective layer of basic zinc carbonate.
$$\ce{4Zn + 3H2O + 2O2 + CO2->$\underset{\text{Basic zinc carbonate}}{\ce{ZnCO3.3Zn(OH)2}}$}$$

7. Mention one use of white vitriol and philoshoper’s wool.

Ans: White vitriol is used in medicine as zinc tablet.
Philoshoper’s wool is used in the manufacture of glass and pottery glaze.

8. What is the action of heat on white vitriol ?

Ans:\ce{ZnSO4.7H2O->[{100^{\circ}C}]ZnSO4.6H2O->[{300^{\circ}C}]ZnSO4->[{800^{\circ}C}]ZnO + SO2 + O2}

9. What happens when zinc oxide is heated with barium sulphate ?

Ans: Zinc sulphate reacts with barium sulphate to give lithophone. Lithophone is used as a white paint.
$$\ce{ZnSO4 + BaS->$\underset{\text{Lithophone}}{\ce{ BaSO4 + ZnS }}$}$$

10. Write the reaction of zinc with hot and concentrated NaOH.

Ans: When zinc is dissolved in hot and concentrated NaOH, sodium zincate is formed.
$$\ce{Zn + 2NaOH->[\Delta]$\underset{\text{Sodium zincate}}{\ce{Na2ZnO2 }}$ + H2 ^ }

11. Write one method of preparation of zinc oxide.

Ans: It is prepared by heating zinc carbonate.
$$\ce{ZnCO3->[\Delta]ZnO + CO2}$$

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