Question

To neutralise completely $20$ mL of $0.1M$ aqueous solution of phosphorous acid ($H_{3}P{O}_3$), the volume of $0.1M$ aqueous $KOH$ solution required is:

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

Answer 1

The correct option is C $40$ mL

As we know, $H_{3}P{O}_3$ is a dibasic acid and so, for complete neutralisation, the volume of $NaOH$ required is $40$ mL.

During neutralisation,

Meq. of $H_{3}P{O}_3=$ Meq. of $KOH$

$M_1\times V_1\times {N_{factor}}_1=M_2\times V_2\times {N_{factor}}_2$

$20\times 0.1\times 2=0.1\times 1\times V_2$

$⟹$ $V_2=40$ mL

Hence, the correct option is $C$