Question

${\text{ZnC}}{{\text{O}}_3}$ is precipitated from ${\text{ZnS}}{{\text{O}}_4}$ solution by the addition of:
A. ${\text{N}}{{\text{a}}_2}{\text{C}}{{\text{O}}_3}$
B. ${\text{CaC}}{{\text{O}}_3}$
C. ${\text{MgC}}{{\text{O}}_3}$
D. ${\text{NaHC}}{{\text{O}}_3}$

Answer 1

This is based on reactivity series. It is based on the ability to displace other elements. It is caused due to the stability of electronic configurations as atoms and ions. Metals which need a loss of one electron to form stable ions are more active than metals which need a loss of more than one electron to form stable ions.

Complete step by step answer:
There are six types of chemical reactions. They are:
Combination reaction
Decomposition reaction
Displacement reaction
Double displacement reaction
Neutralization reaction
Combustion reaction
Double displacement reactions swap elements between two compounds that react together to form two new compounds. Two compounds react, with elements switching places between the original compounds.
According to activity series, magnesium is more active than zinc. Therefore zinc cannot be displaced by magnesium. Similarly calcium is more active than zinc. So zinc cannot be displaced by calcium. Hence the only option is ${\text{N}}{{\text{a}}_2}{\text{C}}{{\text{O}}_3}$.
When ${\text{N}}{{\text{a}}_2}{\text{C}}{{\text{O}}_3}$ reacts with ${\text{ZnS}}{{\text{O}}_4}$, it forms a precipitate ${\text{ZnC}}{{\text{O}}_3}$.
The balanced chemical reaction is given below:
${\text{ZnS}}{{\text{O}}_4} + {\text{N}}{{\text{a}}_2}{\text{C}}{{\text{O}}_3} \to {\text{ZnC}}{{\text{O}}_3} + {\text{N}}{{\text{a}}_2}{\text{S}}{{\text{O}}_4}$
This reaction is a double displacement reaction. ${\text{Zn}}$ is displaced with ${\text{Na}}$. The product combination comes from the positive and negative ions of the two compounds switching places is ${\text{ZnS}}{{\text{O}}_4}$.
Hence option A is correct.
Additional information:
Zinc carbonate is used for various purposes. Some of them are:
-Ointments
-Absorbent
-Oil treatment of pruritus
-Pigments for painting and agriculture stuff

Note:
Reactivity series is used to determine the activity of each element, i.e. the products of single and double displacement reactions. It decides whether an element displaces another element or not. Metal with high activity displaces metal with low activity.