Question

100 mL of pH = 6 (acidic) is diluted to 1000 mL by H₂O. pH will increase approximately by:

(a) 9 unit 

(b) 1 unit

(c) 0.7 unit 

(d) –0.7 unit

Answer 1

Correct option: (c) 0.7

Explanation: 

On dilution,

N₁V₁ = N₂V₂

10^–6 x 100 = N₂ x 1000

N₂ = 10^–7 N

Since acid solution has pH < 7, it will remain acidic even after dilution,

Hence, total [H⁺] = [H⁺]acid + [H⁺]_water

= 10^–7 + 10^–7 = 2 x 10^–7 N

∴ pH = – log [H⁺] = – log (2 x 10^–7) = 7 – log 2

= 6.7

Thus, change in pH = 0.7 unit