Question

Consider following experiments :
(i) $ZnC{l}_2+H_{2}Sgas⟶$ no precipitate
(ii) $(C{H}_{3}COO{)}_{2}Zn+H_{2}Sgas⟶$ white precipitate
(iii) $(C{H}_{3}COO{)}_{2}Zn+dil.HCl+H_{2}Sgaslongrightarrow$ no precipitate
Observation in each case :
(i) is due to ZnS is not precipitated in presence of HCl which is formed in following reaction:
$ZnC{l}_2+H_{2}S⟶ZnS+2HCl$.
(ii) is due to $C{H}_{3}COOH$ does not dissolve ZnS which remains insoluble.
(iii) is due to Medium is HCl and ZnS is dissolved.
Which of these observations are true?

• A. Only (i) true
• B. Only (ii) true
• C. Only (iii) true
• D. All are true

Answer 1

Answer: (D)

All are true

ZnS is soluble in dil HCl solution but it is insoluble in acetic acid.
(i) Thus when zinc chloride is treated with hydrogen sulphide, no precipitate is obtained.
$ZnC{l}_2+H_{2}S⟶ZnS+2HCl$.
(ii) $(C{H}_{3}COO{)}_{2}Zn+H_{2}S⟶\underset{soluble}{ZnS}+C{H}_{3}COOH$
(ii) When zinc acetate is treated with HCl and $H_{2}S$ , zinc sulphide and acetic acid are obtained. But since HCl is present, ZnS is soluble and no precipitate is obtained.

$(C{H}_{3}COO{)}_{2}Zn+dil.HCl+H_{2}S⟶ZnS+C{H}_{3}COOH+HCl$