Question

Which of the following solution will have pH close to 1.0 ?

• A. 100 ml of M/100 HCl + 100 ml of M/10 NaOH
• B. 55 ml of M/10 HCl + 45 ml of M/10 NaOH
• C. 10 ml of M/10 HCl + 90 ml of M/10 NaOH
• D. 75 ml of M/5 HCl + 25 ml of M/5 NaOH

Answer 1

Answer: (D)

75 ml of M/5 HCl + 25 ml of M/5 NaOH

Answer 2

(1) is exact neutralisation. Hence pH = 7

(2) After neutralisation, $\frac{M}{10}$ HCl left = 10 ml.

Total volume = 100 ml.

Dilution = 10 times \ [H⁺] = 10^–2

or pH = 2.

(3) After neutralisation, $\frac{M}{10}$ NaOH left = 80 ml.

Total volume = 100 ml. pH > 7

(4) After neutralisation, $\frac{M}{5}$ HCl left = 50 ml

Total volume = 100 ml

Dilution = 2 times.