JEE Main 2022 · 25 Jul · Shift 1 · Chemistry Q64

ChemistrySingle correct+4 / -1Question 64 of 90

20 mL of 0.1 M $\mathrm{NH_4OH}$ is mixed with 40 mL of 0.05 M HCl. The pH of the mixture is nearest to :

(Given : $K_b(\mathrm{NH_4OH})=1\times10^{-5}$ , log 2 = 0.30, log 3 = 0.48, log 5 = 0.69, log 7 = 0.84, log 11 = 1.04)

3.2

4.2

5.2

6.2

Answer and worked solution

Official answer: C

Exact neutralisation. 2 mmol $\mathrm{NH_4Cl}$ in 60 mL: $c=\frac1{30}$ M.

Salt hydrolysis. pH $=7-\frac12pK_b-\frac12\log c=7-2.5+0.74\approx5.2$ .

(C)

Topics:Hydrolysis of salts

JEE Main 2022 · 25 Jul · Shift 1, Chemistry question 64