A mixture consisting of $4.6 \mathrm{~g}$ of formic acid and $9.0 \mathrm{~g}$ of oxalic acid is str

Question

A mixture consisting of $4.6 \mathrm{~g}$ of formic acid and $9.0 \mathrm{~g}$ of oxalic acid is strongly treated with concentrated $\mathrm{H}_2\mathrm{SO}_4$. The evolved gaseous mixture is completely passed through KOH pellets. The weight (in grams) of the remaining final product gas at STP will be

Professor PC Thomas Classes · Answer

(b) : When treated with conc. $\mathrm{H}_2\mathrm{SO}_4$, formic acid ($\mathrm{HCOOH}$) undergoes dehydration: $\mathrm{HCOOH} ightarrow \mathrm{CO} + \mathrm{H}_2\mathrm{O}$. Moles of $\mathrm{HCOOH} = \frac{4.6}{46} = 0.1 \mathrm{~mol}$, producing $0.1 \mathrm{~mol}$ of $\mathrm{CO}$. Oxalic acid ($\mathrm{H}_2\mathrm{C}_2\mathrm{O}_4$) also undergoes dehydration: $\mathrm{H}_2\mathrm{C}_2\mathrm{O}_4 ightarrow \mathrm{CO} + \mathrm{CO}_2 + \mathrm{H}_2\mathrm{O}$. Moles of $\mathrm{H}_2\mathrm{C}_2\mathrm{O}_4 = \frac{9.0}{90} = 0.1 \mathrm{~mol}$, producing $0.1 \mathrm{~mol}$ of $\mathrm{CO}$ and $0.1 \mathrm{~mol}$ of $\mathrm{CO}_2$. Conc. $\mathrm{H}_2\mathrm{SO}_4$ thoroughly absorbs all the water. The remaining gases are $\mathrm{CO}$ and $\mathrm{CO}_2$. Passing this mixture through KOH completely absorbs the acidic $\mathrm{CO}_2$. The only remaining gas is $\mathrm{CO}$. Total moles of $\mathrm{CO} = 0.1 + 0.1 = 0.2 \mathrm{~mol}$. Mass of $\mathrm{CO} = 0.2 	imes 28 \mathrm{~g/mol} = 5.6 \mathrm{~g}$.