In which of the following cases is the final solution (298 K) basic, i.e. pH > 7? Data: K_a(CH3COOH) = 1.8x10^-5, K_b(NH3) = 1.8x10^-5, K_a(HCN) = 4.0x10^-10.

50 mL of 0.1 M CH3COOH + 50 mL of 0.1 M NaOH

50 mL of 0.1 M NH3 + 50 mL of 0.1 M HCN

50 mL of 0.1 M CH3COOH + 50 mL of 0.1 M NaOH

50 mL of 0.1 M NH3 + 50 mL of 0.1 M HCl

40 mL of 0.1 M CH3COOH + 20 mL of 0.1 M NaOH

50 mL of 0.1 M NH3 + 50 mL of 0.1 M HCN

JEE Advanced levelOne or more correct optionsDifficulty 3 of 3ia019

In which of the following cases is the final solution (298 K) basic, i.e. pH > 7? Data: $K_{a} (CH X_{3} COOH) = 1.8 \times 1 0^{- 5}$ , $K_{b} (NH X_{3}) = 1.8 \times 1 0^{- 5}$ , $K_{a} (HCN) = 4.0 \times 1 0^{- 10}$ .

A gives sodium acetate (basic). B gives

NH X_{4} Cl

(acidic). C is an acetic acid / acetate buffer with equal amounts left, pH

= p K_{a} = 4.74

, acidic. D gives

NH X_{4} CN

with

p K_{a} - p K_{b} = 4.65

, so pH

= 9.33

, basic. Answer A and D.