MCQ
A mixture of $2.3\; \mathrm{g}$ formic acid and $4.5 \;\mathrm{g}$ oxallic acid is treated with conc. $\mathrm{H}_{2} \mathrm{SO}_{4}$. The evolved gaseous mixture is passed through KOH pellets. Weight  of the remaining product at $STP$ ..........$g$
  • A
    $1.4$
  • B
    $3$
  • $2.8$
  • D
    $4.4$

Answer

Correct option: C.
$2.8$
c
$\mathrm{HCOOH} \xrightarrow[dehydrating Agent]{H_2SO_4} \mathrm{CO}+\mathrm{H}_{2} \mathrm{O}\left(\begin{array}{l}{\mathrm{H}_{2} \mathrm{O}\text { abosrbed }} \\ {\mathrm{by} \mathrm{H}_{2} \mathrm{SO}_{4}}\end{array}\right)$

(moles)$_{1}=\frac{2.3}{46}=\frac{1}{20} \quad \quad 0 \quad \quad \quad 0$

(moles)$_f 0\quad \quad \quad \quad \quad \quad \frac{1}{20}\quad \quad \quad \frac{1}{20}$

$\quad \quad \mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4} \stackrel{\mathrm{H}_{2} \mathrm{SO}_{4}}{\longrightarrow} \mathrm{CO}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}$

$\left[\mathrm{H}_{2} \mathrm{O} \text { absorbed by } \mathrm{H}_{2} \mathrm{SO}_{4}\right]$

(moles)$_1\quad \frac{4.5}{90}=\frac{1}{20} 0 \quad \quad \quad 0 \quad \quad 0$

(moles)$_f\quad 0\quad \quad \quad \ \frac{1}{20} \quad \quad \frac{1}{20} \quad \quad \frac{1}{20}$

$\mathrm{CO}_{2}$ is absorbed by KOH. So the remaning product is only CO. moles of CO formed from both reactions

$=\frac{1}{20}+\frac{1}{20}=\frac{1}{10}$

Left mass of $\mathrm{CO}=$ moles $\times$ molar mass

$=\frac{1}{10} \times 28$

$={2.8 \mathrm{g}}$

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