Chemistry · Some Basic Concepts Of Chemistry · NEET
Only carbon monoxide (CO). Conc. H2SO4 removes one water molecule from formic acid: HCOOH → CO + H2O. So formic acid (HCOOH) loses H2O and what is left is just CO. There is no CO2 here. Remember: formic acid has only ONE carbon, so it can only make ONE carbon gas, which is CO.
Oxalic acid, (COOH)2, has TWO carbons. When conc. H2SO4 removes water from it, the two carbons split into two different gases: (COOH)2 → CO + CO2 + H2O. One carbon becomes CO and the other becomes CO2. So you always get an equal number of moles of CO and CO2 from oxalic acid.
Conc. H2SO4 acts as a dehydrating agent. 'Dehydrate' means to remove water. H2SO4 does not become part of the products; it just grabs the water (H2O) that comes out of the acid. Because it removes water, the acid is forced to break down and release gases. It is not acting as an acid or an oxidiser here, only as a water remover.
KOH (potassium hydroxide) is a base. It reacts with and absorbs the acidic gas CO2, forming K2CO3. But KOH does NOT react with CO, because CO is a neutral gas. So after you pass the gas mixture through KOH, only CO is left. This is the standard NEET trick: KOH removes CO2, CO passes through.
Yes, both reactions are done on warming with conc. H2SO4. Formic acid gives CO on warming with conc. H2SO4, and oxalic acid gives CO + CO2 on heating with conc. H2SO4. In NEET numerical problems the heating is assumed; you focus on the products and the moles.
First find moles of each acid using moles = mass / molar mass. Molar mass of HCOOH = 46 g/mol and of (COOH)2 = 90 g/mol. Then use the balanced reaction: 1 mole HCOOH gives 1 mole CO; 1 mole oxalic acid gives 1 mole CO plus 1 mole CO2. Add up the CO from both and the CO2 from oxalic acid.
A mixture of 2.3 g formic acid (HCOOH) and 4.5 g oxalic acid ((COOH)2) is treated with conc. H2SO4. The evolved gaseous mixture is passed through KOH pellets. The weight (in g) of the remaining gas is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Formic acid gives only CO. Oxalic acid gives both CO and CO2 in equal moles. This is because formic acid has one carbon and oxalic acid has two carbons.
No. Here conc. H2SO4 acts only as a dehydrating agent. It removes water (H2O) from the acids and does not oxidise them or enter the products.
CO (carbon monoxide) is a neutral gas, so it does not react with the base KOH. Only the acidic gas CO2 reacts with KOH and is absorbed. This lets you separate CO from CO2.
Formic acid HCOOH = 46 g/mol, oxalic acid (COOH)2 = 90 g/mol, CO = 28 g/mol, CO2 = 44 g/mol. These four values solve almost every version of this NEET question.
NEET has directly asked a numerical from this exact reaction (2018). It combines gas identification (CO vs CO2), the KOH absorption trick, and mole calculations in one question, so it tests several skills at once.
