The density of x M NaOH solution is 1.12 g mL⁻¹ – JEE Main PYQ

JEE Main Previous Year Question

Q. The density of ‘x’ M solution (‘x’ molar) of NaOH is 1.12 g mL⁻¹, while in molality, the concentration of the solution is 3 m (3 molal). Then x is.

(Given: Molar mass of NaOH is 40 g mol⁻¹)

A. 3.8

B. 3.0

C. 3.5

D. 2.8

Detailed Solution:

Molality (m) is defined as:

m = moles of solute / kg of solvent

Given molality = 3 m So, moles of NaOH = 3 moles Mass of NaOH = 3 × 40 = 120 g

Let mass of solvent = 1 kg = 1000 g Total mass of solution = 1000 + 120 = 1120 g

Density of solution = 1.12 g mL⁻¹

Volume of solution =

Volume = Mass / Density = 1120 / 1.12 = 1000 mL = 1 L

Molarity (x) = moles of solute / volume (in L)

x = 3 / 1 = 3.0 M

Correct Answer: 3.0