Question

A mono basic acid is dissociated to 25% in 0.1 N solution. When 100 mL of the acid is neutralized by 0.1 $N$ KOH solution, heat evolved was 120 cal. Heat of dissociation per mole of acid in kcal is (nearest integer)________.

Answer 1

Total number of moles of acid neutralized $=0.1N\times 0.1L=0.01mol$

The heat evolved $=120cal$.

Hence, the heat evolved per mole $=\frac{120cal}{0.01mol}=12000cal=12kcal$

The heat of naturalization of a proton with hydroxide ion is -13.7 kcal/mol.

Hence, the heat of dissociation per mol of acid $=13.7-12=1.7\approx 2kcal$ .