© All Rights reserved @ LearnWithDash
Step-by-Step Solution
Step 1: Identify the Reactions
When formic acid ($HCOOH$) is heated with concentrated $H_{2}SO_{4}$, it decomposes to give carbon monoxide ($CO$) and water ($H_{2}O$). Similarly, oxalic acid ($H_{2}C_{2}O_{4}$) in the presence of conc. $H_{2}SO_{4}$ decomposes to produce carbon monoxide ($CO$), carbon dioxide ($CO_{2}$), and water ($H_{2}O$). These reactions are:
1) $HCOOH \xrightarrow{H_{2}SO_{4}} CO + H_{2}O$
2) $H_{2}C_{2}O_{4} \xrightarrow{H_{2}SO_{4}} CO + CO_{2} + H_{2}O$
Step 2: Calculate the Moles of Each Acid
Molar mass of formic acid ($HCOOH$) = $46\,g/mol$.
Given mass = $2.3\, g$.
Moles of formic acid = $\dfrac{2.3}{46} = \dfrac{1}{20}$.
Molar mass of oxalic acid ($H_{2}C_{2}O_{4}$) = $90\,g/mol$.
Given mass = $4.5\, g$.
Moles of oxalic acid = $\dfrac{4.5}{90} = \dfrac{1}{20}$.
Step 3: Determine the Moles of Gases Produced
From $HCOOH$, each 1 mole produces 1 mole of $CO$. Since we have $\dfrac{1}{20}$ mole of formic acid, it produces $\dfrac{1}{20}$ mole of $CO$.
From $H_{2}C_{2}O_{4}$, each 1 mole produces 1 mole of $CO$ and 1 mole of $CO_{2}$. With $\dfrac{1}{20}$ mole of oxalic acid, we get $\dfrac{1}{20}$ mole of $CO$ and $\dfrac{1}{20}$ mole of $CO_{2}$.
Therefore, total $CO$ formed is
$$
\dfrac{1}{20} + \dfrac{1}{20} = \dfrac{1}{10}.
$$
Also, $CO_{2}$ formed is $\dfrac{1}{20}$ mole, while water is produced but remains absorbed by conc. $H_{2}SO_{4}$ during the reaction.
Step 4: Action of KOH Pellets on the Gaseous Mixture
The mixture of $CO$ and $CO_{2}$ is passed through KOH pellets. KOH absorbs $CO_{2}$, leaving $CO$ unabsorbed. Hence, only $CO$ remains in the final gaseous product.
Step 5: Calculate the Mass of the Remaining Gas (CO)
The total moles of $CO$ after absorption is $\dfrac{1}{10}$ as found above.
Molar mass of $CO$ = $28\, g/mol$.
Hence, mass of $CO$ =
$$
\dfrac{1}{10} \times 28 = 2.8\, g.
$$
Step 6: Conclude the Correct Answer
Hence, after passing the evolved gases through KOH pellets, the weight of the remaining product (which is $CO$) at STP is $2.8\, g$.
