Question

20 gm of solid NaOH is dissolved in 800 ml water. The solution is treated with 250 ml 0.8M HC/ solution. The resulting solution is diluted to 2 liter. 100 ml of this diluted solution requires V ml 0.25 M H${}_2$SO${}_4$ for complete neutralisation. The value of V is :

• A. 600
• B. 30
• C. 60
• D. 100

Answer 1

The correct option is B 30

$20$g $NaOH=1/2$ mole in $800$ml water

$M=1/2\times \frac{1000}{800}=5/8M$

$250$ml $0.8M$ $HCl$ is added

Now, conc. after addition diluted 2 lit $=\frac{800\times \frac{5}{8}-250\times 0.8}{2000}\approx 0.15M$

Now for $H_2{SO}_4$

$N_1{V}_1=N_2{V}_2$

$100\times 0.15=2\times 0.25\times V$

$V=30ml$