Calculate the concentration of H + (aq) in 0 · 2 M solution of HCN . Given that the dissociation constant of HCN in water is 4 . 9 × 10 - 10 .

Here, C = 0 . 2 M K a = 4 . 9 × 10 - 10 HCN ⇌ H + aq + CN − aq Initial 0 . 2 M At Eq. 0 .2 − x x x K a = x . x 0 .2 − x 4 .9 × 10 − 10 = x 2 0 .2 − x [ 0 .2 − x ≈ 0 . 2 ( ∵ HCN is a weak acid ) ] 0 .2 × 4 .9 × 10 − 10 = x 2 x = 9 .8 × 10 − 11 = 98 × 10 − 12 = 9 .9 × 10 − 6 M Therefore, the concentration of H + is 9 .9 × 10 − 6 M

If hydrogen ion concentration in a solution is 1 × 10 - 5 moles / litre , calculate the concentration of OH - ion in this solution ( K w = 10 - 14 moles 2 / litre 2 ) .

Given, [ H + ] = 1 × 10 - 5 moles / litre K w = 10 - 14 moles 2 / litre 2 ∵ K w = [ H + ] [ OH - ] ∴ [ OH - ] = K w [ H + ] = 10 - 14 1 × 10 - 5 = 10 - 9 moles / litre

What is the pH of a solution whose H + ion concentration is 2 × 10 - 5 g ions / litre ?

Given:- [ H + ] = 2 × 10 - 5 g ions / litre Now, g ions = moles ∴ [ H + ] = 2 × 10 - 5 M ∴ pH = - log [ H + ] = - log ( 2 × 10 - 5 ) = - log ( 2 ) + 5 = - 0 . 3010 + 5 = 4 . 6990 Note:- pH is a quantitative measure of the acidity or basicity of aqueous or other liquid solutions.

Calculate the pH of a solution which is 1 × 10 - 3 M with respect to sulphuric acid.

H 2 SO 4 is a diprotic acid. 1 × 10 - 3 M with respect to sulphuric acid means, H + = 2 × 10 − 3 of the given acid. ∴ pH = - log H + = - log 2 × 10 - 3 = - log 2 + 3 = 3 - 0 . 3010 = 2 . 699