What mass of NaOH should be dissolved in sufficient water to get 20 m3 of an aqueous solution of pH

Question

What mass of NaOH should be dissolved in sufficient water to get 20 m3 of an aqueous solution of pH 7.3 at 25o C?

Accepted Answer

PH is close to 7.0 and hence, contribution of water is considered. Let water dissociates only upto ‘x’ M is presence of CM-NaOH.

H₂O $\rightleftharpoons$ H⁺ + OH^–

Equilibrium x M (x + C) M

Now, x = 10^–7.3 and $x + C = \frac{10^{- 14}}{x} = 10^{- 6.7}$

∴ C = 10^–6.7 – 10^–7.3 = 2 × 10^–7 – 5 × 10^–8 = 1.5 × 10^–7 M

∴ Mass of NaOH = (20 × 10³) × 1.5 × 10^–7 × 40 = 0.12 gm

Question