Question

The density of 'x' M solution ('x' molar) of NaOH is $1.12 \, \text{g/mL}$. While in molality, the concentration of the solution is $3 \, \text{m}$ (3 molal). Then x is:
Given: Molar mass of NaOH is $40 \, \text{g/mol}$

• A. 3.5
• B. 3
• C. 3.8
• D. 2.8

Answer 1

Answer: (B)

3

Answer 2

We know the relationship between molality and molarity:
$\text{Molality} = \frac{1000 \times M}{1000 \times d - M \times (\text{Molar mass of solute})}$
Substituting the values:
$3 = \frac{1000 \times x}{1000 \times 1.12 - x \times 40}$
Rearranging:
$3 \times (1000 \times 1.12 - x \times 40) = 1000 \times x$
Simplify:
$3 \times 1120 - 120x = 1000x$
$3360 = 1120x$
Solving:
$x = 3$
Thus, the molarity of the solution is 3.0 M.