Which of the following aqueous solutions will exhibit the highest boiling point?

Question

$W$ g of a non-volatile electrolyte solid solute of molar mass $M\,\text{g mol}^{-1}$ when dissolved in $100\,\text{mL}$ water decreases vapour pressure of water from $640\,\text{mm Hg}$ to $600\,\text{mm Hg}$. If aqueous solution of the electrolyte boils at $375\,\text{K}$ and $K_b$ for water is $0.52\,\text{K kg mol}^{-1}$, then the mole fraction of the electrolyte $(x_2)$ in the solution can be expressed as ___.
(Given: density of water $=1\,\text{g mL}^{-1}$, boiling point of water $=373\,\text{K}$)

Answer 1

The boiling point elevation is directly proportional to the molality of the solution and the van 't Hoff factor $ i $, which represents the number of particles the solute dissociates into.

- KNO₃ dissociates into 2 ions (K$^+$ and NO₃$^-$), yielding $ i = 2 $.
- H₂SO₄ dissociates into 3 ions (H$^+$, HSO₄$^-$, and SO₄²⁻), resulting in $ i = 3 $.
- C₆H₁₂O₆ (glucose) does not dissociate, so $ i = 1 $.
- Urea also does not dissociate into ions, hence $ i = 1 $.

Because boiling point elevation is proportional to $ i $, the solution with the highest van 't Hoff factor will exhibit the highest boiling point.
Consequently, H₂SO₄ (dissociating into 3 ions) will have the highest boiling point.

Therefore, the correct selection is (2) 0.01M H₂SO₄.

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Which of the following aqueous solutions will exhibit the highest boiling point?

Show Hint

The Correct Option is B

Solution and Explanation

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