Question

A mixture of 2.3 g formic acid and 4.5 g oxalic acid is treated with conc. ${{H}_{2}}S{{O}_{4}}$. The evolved gaseous mixture is passed through KOH pellets. Weight (in g) of the remaining product at STP will be:
A. 2.8
B. 1.4
C. 4.4
D. 3.0

Answer 1

When $KOH$ absorbs all $C{{O}_{2}}$, ${{H}_{2}}O$ is absorbed by ${{H}_{2}}S{{O}_{4}}$. The remaining product is $CO$. Use the formula $\text{no}\text{. of moles = }\dfrac{\text{weight}}{\text{molecular mass}}$ to carry out the calculations.

Complete step by step answer:
With the given information, we can obtain the following chemical equations:
$1)HCOOH\xrightarrow[KOH\text{ pellets}]{{{H}_{2}}S{{O}_{4}}}CO+{{H}_{2}}O$
$2)HOOC-COOH\xrightarrow[KOH\text{ pellets}]{{{H}_{2}}S{{O}_{4}}}CO+C{{O}_{2}}+{{H}_{2}}O$

We know that concentrated ${{H}_{2}}S{{O}_{4}}$ is a strong dehydrating agent.
Moles of $HCOOH=\dfrac{2.3}{46}=0.05\text{ }mole$
Moles of $HOOC-COOH=\dfrac{2.3}{46}=0.05\text{ }mole$
From reaction 1),
We know that the number of $CO$ formed is 0.05 mole
From reaction 2),
Number of $CO$ formed is 0.05 mole
Number of $C{{O}_{2}}$ formed is 0.05 mole

Therefore, total number of moles of $CO$ formed is $0.05mol+0.05mol=0.1mol$
And, total number of moles of $C{{O}_{2}}$ formed is 0.05 mole
As, we know that KOH pellets absorb all $C{{O}_{2}}$, and ${{H}_{2}}O$ is absorbed by ${{H}_{2}}S{{O}_{4}}$. Therefore, $CO$ is the remaining product.
Hence, the weight of the remaining product $=\text{ }0.1\times 28\text{ }=\text{ }2.8g$
Since the molecular mass of $CO$ is 28 we have multiplied it with the number of moles obtained to get the mass of the product obtained.
So, the correct answer is “Option A”.

Note: We know that a substance that absorbs moisture from its surroundings is called a dehydrating agent. Sulfuric acid really put on its water leading to the formation of hydronium Ion so it acts as a good dehydrating agent.
Potassium hydroxide pellets are odourless, white, solid hemispheres of uniform diameter and thickness. Their geometry reduces dusting and kicking so that the product stores and handles better. They are stored in air tight containers as they easily absorb moisture from the air and become sticky.