Question

A mixture of formic acid and oxalic acid is heated with concentration $H_{2}S{O}_4$. The gases produced are collect and on its treatment, with a $KOH$ solution the volume of the gas decreased by one-sixth. Calculate the molar ratio of the two acids in the original mixture.

Answer 1

Concentrated $H_{2}S{O}_4$ is a dehydrating agent.

$HCOOH+H_{2}S{O}_4⟶CO+H_{2}S{O}_4\cdot H_{2}O$

$H_2{C}_2{O}_4+H_{2}S{O}_4⟶CO+C{O}_2+H_{2}S{O}_4\cdot H_{2}O$

Let moles of $HCOOH$ be $x$ and moles of $H_2{C}_2{O}_4$ be $y$

$\therefore$ Moles of $CO$ produced from $HCOOH=x$

Moles of $CO$ produced from $H_2{C}_2{O}_4=y$

Moles of $C{O}_2$ produced from $H_2{C}_{2}O=y$

Total moles of gases $=(x+2y)$ of which $C{O}_2$ is $y$ $moles$

On heating with $KOH$, $C{O}_2$ is absorbed

Volume decreased by ${1/6}^{th}$

$\therefore$ Fraction of $C{O}_2$ present $=\frac{1}{6}=\frac{y}{x+2y}$

$⟹x+2y=6y$

$⟹x=4y$

$\therefore x:y=4:1$

$HCOOH:H_2{C}_2{O}_4=4:1$