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# Assuming 100% ionization in case of strong electrolytes which of the following will have minimum $pH$?

(a) 0.01 M $NH_4Cl$

(b) 0.01 M $(NH_4)_2SO_4$

(c) 0.01 M $(NH_4)_3PO_4$

(d) All will have same $pH$

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A)
Answer: $0.01 M (NH_4)_2SO_4$

Minimum $pH$ means maximum $[H^+]$

$NH_4Cl \longrightarrow NH_4^+ + Cl^-$

$NH^+_4 + H_2O \rightleftharpoons NH_4OH + H^+$

$\therefore [H^+] = 0.01 \times K_h$

In case of $(NH_4)_2SO_4$, $[H^+] = 0.02 \times K_h$

However $(NH_4)_3PO_4$ wil be almost neutral ($pH \approx 7$) as it is a salt of a weak acid and a weak base. Thus pH will be minimum (i.e., highest $H^+$ concentration) in case of 0.01 M $(NH_4)_2SO_4$.