Q4 / 180 · COMEDK 2023 (Morning Shift) · Chemistry

$5\text{ g}$ of a non-volatile, water-soluble compound $X$ is dissolved in $100\text{ g}$ of water ($K_b = 0.52\text{ K kg mol}^{-1}$). The elevation in boiling point is found to be $1.3\text{ K}$. The molar mass of compound $X$ is:

  • Correct answer
    A
    20 g
  • B
    35 g
  • C
    40 g
  • D
    60 g

Solution

$\Delta T_b = K_b \cdot m = \dfrac{K_b \cdot w_2}{M_2 \cdot w_1}$

$M_2 = \dfrac{K_b \cdot w_2}{\Delta T_b \cdot w_1} = \dfrac{0.52 \times 5}{1.3 \times 0.1} = \dfrac{2.6}{0.13} = 20$ g/mol

Hence, the correct answer is option: 'A'.

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