Question

Identify the compound that is base-insoluble. Identify the compound that is base-insoluble. ZnS KCl PbCl2 As2S3 Ca3(PO4)2

Please explain why. Thank you.

Answer 1

Answer: ZnS

Explanation

KCl, PbCl₂, As₂S₃ and Ca₃(PO₄)₂ are soluble in base because of the following reactions

i) KCl $\rightleftharpoons$ K⁺ + Cl^-

K⁺ + OH^- $\rightarrow$ KOH

ii) PbCl₂   $\rightleftharpoons$ Pb²⁺ + 2Cl^-

Pb²⁺ + 2OH^- $\rightarrow$    Pb(OH)₂

iii) As₂S₃   $\rightleftharpoons$ 2As³⁺ + 3S^2-

As³⁺ + 3OH^-   $\rightarrow$ As(OH)₃

iv) Ca₃(PO₄)₂        $\rightleftharpoons$       Ca₃(PO₄)₂

Ca²⁺ + 2OH^-    $\rightarrow$ Ca(OH)₂

Ksp of ZnS is very small ( 2 x 10^-25 ). Therefore, ZnS will not dissociate appreciably in to the constituent ions and therefore will not dissolve in base