JEE Main 2025 — Some Basic Concepts Of Chemistry Question with Solution

Step 1: Calculate the pressure of dry nitrogen gas

The nitrogen gas was collected over water, so we subtract the aqueous tension (pressure of water vapor) from the total pressure to find the pressure of dry nitrogen gas.

$$\text{Pressure of dry }{\mathrm{N}}_2=715\mathrm{mm}\mathrm{Hg}-15\mathrm{mm}\mathrm{Hg}=700\mathrm{mm}\mathrm{Hg}$$

Now, convert this pressure from mm Hg to atm:

$$700\mathrm{mm}\mathrm{Hg}÷760=\frac{700}{760}\mathrm{atm}$$

Step 2: Use the ideal gas equation to find moles of nitrogen

The volume of nitrogen ($V$) is given as 60 mL. Convert this to liters: 60 mL = 0.060 L (or use $60\times 10^{-3}$ L). The temperature ($T$) is 300 K, and the gas constant ($R$) is 0.0821 L·atm·K⁻¹·mol⁻¹.

Using the formula $\mathrm{n}=\frac{\mathrm{PV}}{\mathrm{RT}}$:

$$\mathrm{n}=\frac{700\times 60\times 10^{-3}}{760\times 0.0821\times 300}$$

When you calculate this, you get: $$\mathrm{n}=0.0022\text{mole}$$

Step 3: Calculate the mass of nitrogen gas produced

Moles of nitrogen are 0.0022. The molar mass of ${\mathrm{N}}_2$ is 28 g/mol.

$$\text{Mass of }{\mathrm{N}}_2=0.0022\times 28=0.063\mathrm{g}$$

Step 4: Find the percentage of nitrogen in the compound

The mass of organic compound taken is 0.4 g. To find the percentage of nitrogen:

$$\text{Percentage of nitrogen}=\frac{\text{Mass of }{\mathrm{N}}_2}{\text{Mass of compound}}\times 100$$

$$=\frac{0.063}{0.4}\times 100=15.71\%$$