A mixture of 2.3 g formic acid and 4.5 g oxalic acid is treated with conc. H2SO4
. 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

To solve this problem, we need to understand the chemical reactions involved and calculate the masses of the reactants and products.

The reaction between formic acid (HCOOH) and oxalic acid (H2C2O4) with concentrated sulfuric acid (H2SO4) is as follows:

2HCOOH + H2C2O4 → CO2 + CO + 2H2O

From the balanced equation, we can see that 2 moles of formic acid and 1 mole of oxalic acid produce 3 moles of gas (CO2 and CO) and 2 moles of water.

First, we calculate the moles of formic acid and oxalic acid:

Molar mass of formic acid (HCOOH) = 46.03 g/mol
Molar mass of oxalic acid (H2C2O4) = 90.03 g/mol

Moles of formic acid = mass of formic acid / molar mass of formic acid
= 2.3 g / 46.03 g/mol
≈ 0.05 mol

Moles of oxalic acid = mass of oxalic acid / molar mass of oxalic acid
= 4.5 g / 90.03 g/mol
≈ 0.05 mol

Since both formic acid and oxalic acid have the same number of moles, it means they will react completely.

According to the reaction, 2 moles of formic acid react to produce 3 moles of gas. Therefore, 0.05 moles of formic acid will produce (0.05 mol) x (3 mol of gas/2 mol of formic acid) = 0.075 moles of gas.

The molar mass of the remaining product (CO2 and CO) is 44.01 g/mol.

Weight of the remaining product at STP = moles of the remaining product x molar mass of the remaining product
= 0.075 mol x 44.01 g/mol
≈ 3.3 g

However, we need to account for the fact that the evolved gas mixture is passed through KOH pellets, which will absorb CO2. As a result, the remaining product will be CO.

Since the molar mass of CO is 28.01 g/mol, the weight of the remaining product at STP will be:

Weight of the remaining product at STP = moles of the remaining product x molar mass of the remaining product
= 0.075 mol x 28.01 g/mol
≈ 2.1 g

Therefore, the weight of the remaining product at STP is approximately 2.1 g.

The closest option to 2.1 g among the given choices is 2.8 g, so the correct answer is A. 2.8.