Question

Following solutions were prepared by mixing different volume of NaOH and HC1 of different concetrations:
(1) 60 mL `(M)/(10)` HC1 + 40 mL `(M)/(10)`NaOH
(2) 55 mL `(M)/(10)` HC1 + 45 mL `(M)/(10)` NaOH
(3) 75 mL `(M)/(5)` HC1 + 25 mL `(M)/(5)` NaOH
100 mL `(M)/(10)` HC1 + 100 mL `(M)/(10)` NaOH
pH of which one of them will be equal to 1 ?
A. 1
B. 2
C. 4
D. 3

Answer 1

Correct Answer - D
Where `N_(1) V_(1) gt N_(2)V_(2)`
Acid is left at the end of reaction and solutuion will be acidic
`N_(final solution) = [H^(+)] = (N_(1)V_(1) - N_(2)V_(2))/(V_(1) + V_(2))` , as basicity and acidity of acid and base is 1 so M = N
(1) `[H^(+)] = (6-4)/(100) = (2)/(100)` `pH /+ 1`
(2) `[H^(+)] = (5.5 - 4.5)/(100) = (1)/(100) = 10^(-2)` `pH = 2`
(3) `[H^(+)] = (15 - 5)/(100) = (10)/(100) = 10^(-1)` `pH = 1`
(4) `[H^(+)] = (10 - 10)/(200) = 0` Neutral