Question

To neutralize completely 20 mL of 0.1M aqueous solution of phosphorus acid $(H_3PO_3)$ the volumeof 0.1 M aqueous KOH solution required is

• A. 10 mL
• B. 20 mL
• C. 40 mL
• D. 60 mL

Answer 1

Answer: (C)

40 mL

Answer 2

$H_3PO_3$ is a dibasic acid. ${H_3PO_3 + 2 KOH -> K_2HPO_3 + 2H_2O}$ $\frac{M_AV_A}{n_A} = \frac{M_BV_B}{n_B}$ $\frac{0.1 \times 20}{1} = \frac{0.1 \times V_B}{2}$ $V_B$ = 40 mL.