When `H_(2)S` gas is passed into aq `ZnCl_(2)` solution white ppt of ZnS is obtained. Explain.

Explanation

### Step-by-Step Solution:

1. **Understanding the Reactants**:
- We start with an aqueous solution of zinc chloride (ZnCl₂) and hydrogen sulfide gas (H₂S). Zinc chloride dissociates in water to give zinc ions (Zn²⁺) and chloride ions (Cl⁻).

2. **Reaction of H₂S with Zn²⁺**:
- When H₂S gas is bubbled into the ZnCl₂ solution, the hydrogen sulfide reacts with the zinc ions (Zn²⁺) present in the solution. The sulfide ions (S²⁻) from H₂S combine with Zn²⁺ to form zinc sulfide (ZnS), which is insoluble in water.

3. **Formation of Precipitate**:
- The reaction can be represented as:
\[ \text{ZnCl}_2 (aq) + \text{H}_2\text{S} (g) \rightarrow \text{ZnS} (s) + 2 \text{HCl} (aq) \]
- In this reaction, zinc sulfide (ZnS) precipitates out of the solution as a white solid, while hydrochloric acid (HCl) remains in the solution.

4. **Properties of Zinc Sulfide**:
- Zinc sulfide (ZnS) is known to be insoluble in water and in dilute acids. It appears as a white precipitate when formed.

5. **Further Reactions**:
- If zinc sulfide is treated with caustic soda (sodium hydroxide, NaOH), it can form a white precipitate of zinc hydroxide (Zn(OH)₂). The reaction can be represented as:
\[ \text{ZnS} + 2 \text{NaOH} \rightarrow \text{Zn(OH)}_2 (s) + \text{Na}_2\text{S} \]
- On heating with excess NaOH, sodium zincate (Na₂ZnO₂) is formed:
\[ \text{Zn(OH)}_2 + 2 \text{NaOH} \rightarrow \text{Na}_2\text{ZnO}_2 + 2 \text{H}_2\text{O} \]

6. **Dissolution of Zinc Sulfide**:
- If zinc sulfide is treated with dilute hydrochloric acid, it dissolves to regenerate zinc chloride and hydrogen sulfide:
\[ \text{ZnS} + 2 \text{HCl} \rightarrow \text{ZnCl}_2 + \text{H}_2\text{S} \]

### Summary:
When H₂S gas is passed into an aqueous solution of ZnCl₂, zinc ions react with sulfide ions to form a white precipitate of zinc sulfide (ZnS). This reaction highlights the insolubility of ZnS in water and its behavior in the presence of caustic soda and acids.