Question

Choose the correct statement regarding oxalic acid and malonic acid.

• A. None of the above
• B. Both oxalic and malonic acid has similar ionisation value
• C. First ionisation value of malonic acid is higher than oxalic acid
• D. First ionisation value of oxalic acid is higher than malonic acid

Answer 1

The correct option is D First ionisation value of oxalic acid is higher than malonic acid

The increase in the $C{H}_2$ group in the compound will decrease the acidic strength of the compound because $C{H}_2$ is an $+I$ effect group so, it will increase the electron density on conjugate base.
Oxalic acid doesn't have $+I$ group so it is more acidic.
Hence, the anion formed after the removal of first $H^{+}$ of oxalic acid is more stable due to stronger $-I$ effect of $-COOH$ present at close distance.
Malonic acid has one $C{H}_2$ which shows $+I$ effect and increase electron density and make the conjugate base less stable so it is less acidic.
$\text{Strength of acid}\propto \text{Ionisation value of acid}$
Therefore, the correct option is (a).