Question

Given : Enthalpy of ionization of two acids :
AH (HCN) = 45.2 kJ mol
AH (CH2COOH) = 2.1 kJ mol-
Which relationship for the two acids is true
(1) pK. (HCN)=pK. (CH3COOH)
(2) pK (HCN)> PK (CH3COOH)
(3) pK, (HCN) <pK (CH-COOH)
(4) pK. (HCN) =
45.2
2.1
PK (CH2COOH)
1​

Answer 1

Answer:

(2) pK (HCN)> PK (CH3COOH)

Explanation:

since enthalpy of ionisation of CH₃COOH is less than HCN means CH₃COOH requires less energy to ionise so it is stronger acid compared to HCN as HCN requires more energy to ionise completely in the solution.

pka is inversely proportional to acidity so pka of HCN is more than pka of CH₃COOH