Question

The enthalpy of neutralisation of a weak acid of 1M solution with a strong base is $-56.1$ KJ/ mol . If the enthalpy of ionisation of acid is 1.5 KJ $mo{l}^{-1}$ and enthalpy of neutralisation of the acid with a strong base is $-57.3$ KJ$e{q}^{-1}$, what is the $\%$ ionisation of the weak acid in molar solution?

• A. 25
• B. 20
• C. 15
• D. 10

Answer 1

Answer: (B)

20

Ideally, the enthalpy of neutralization should be - 57.3 K.J + 1.5 K.J $=$ - 55.8 KJ.
But it is - 56.1 KJ.

$\therefore$ Energy used for neutralization $=$ 57.3 - 56.1 $=$ 1.2 KJ
$\therefore$ Percent ionization of weak acid $=\frac{1.5-1.2}{1.5}\times 100$$=$ 20%
$\therefore$ % of week acid in solution $=$ 20%