Question

Heat of neutralisation of $H_{2}C_{2}O_{4}$ (oxalic acid) is $-26\,kcal\,mol^{- 1}$ . Hence, dissociation energy of $H_{2}C_{2}O_{4}\rightleftharpoons2H^{+}+C_{2}O_{4}^{2 -}$ is :

• A. $12.3\,kcal\,mol^{- 1}$
• B. $1.4\,kcal\,mol^{- 1}$
• C. $-13.7\,kcal\,mol^{- 1}$
• D. $-1.4\,kcal\,mol^{- 1}$

Answer 1

Answer: (B)

$H^{+}+OH^{-} \rightarrow H_{2}O;\Delta H=-13.7\,kcal/mole$
Oxalic acid has two ionisable $H^{+}$ ions.
Hence, the expected heat of neutralization, if it behaves strong acid would have been = $-13.7\times 2=-27.4\,kcal\,mol^{- 1}$
But experimental value = $-26\,kcal\,mol^{- 1}$
So dissociation enery = $1.4\,kcal\,mol^{- 1}$ .