Question

By adding 20 ml 0.1 N HCL to 20 ml 0.001 N KOH, the pH of the obtained solution will be
A. 2
B. 1.3
C. 0
D. 7

Answer 1

Correct Answer - B
20 ml. of 0.1N HCl `= (0.1)/(1000) xx 20 eq. = 2 xx 10^(-3) g eq`.
20 ml. of 0.001 KOH `= (0.001)/(1000) xx 20` gm eq.
`= 2 xx 10^(-5)` g eq.
`:.` HCl left unneutralised `= 2(10^(-3) - 10^(-5))`
`= 2 xx 10^(-3) (1- 0.01) = 2 xx 0.99 xx 10^(-3) = 1.98 xx 10^(-3)` g eq.
Volume of solution = 40 ml.
`:. [HCl] = (1.98 xx 10^(-3))/(40) xx 1000 M = 4.95 xx 10^(-2)`.
`:. pH = 2 - log 4.95 = 2 - 0.7 = 1.3`.