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Molar mass of a solute from the depression in freezing point or elevation of boiling point

This type of question, asked 13 times: 2 May 2023 S2, 3 May 2023 S1, 4 May 2023 S1, 10 May 2023 S2, 9 May 2024 S1, 14 May 2024 S2, 25 Apr 2025 S1, 11 Apr 2026 S2, 13 Apr 2026 S1, 17 Apr 2026 S1, 14 May 2026 S2, 19 May 2026 S1, 19 May 2026 S2. All 13 questions below, oldest first.

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  1. Question 1

    2 May 2023 S2

    100
    Calculate the molar mass of a non-volatile solute when 5 g of it is dissolved in 50 g solvent, boils at 119.6∘C119.6^\circ\text{C}. (Kb=3.2 K kg mol−1K_b = 3.2\,\text{K kg mol}^{-1}, boiling point of pure solvent =118∘C= 118^\circ\text{C})

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  2. Question 2

    3 May 2023 S1

    96
    Calculate the molar mass of nonvolatile solute when 1.5 g of it is dissolved in 90 g solvent decreases its freezing point by 0.25 K. [Kf=1.2 K kg mol−1K_f=1.2\ \text{K kg mol}^{-1}]

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  3. Question 3

    4 May 2023 S1

    66
    Calculate the molar mass of non-volatile solute when 1 g of it is dissolved in 100 g solvent decreases its freezing point by 0.2 K. Kf=1.2 K kg mol−1K_f = 1.2\text{ K kg mol}^{-1}

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  4. Question 4

    10 May 2023 S2

    99
    Calculate molar mass of nonvolatile solute if a solution containing 0.35 g solute in 100 g water has boiling point elevation 0.01 K. (Kb=0.50 K kg mol−1K_b = 0.50\,\text{K}\,\text{kg}\,\text{mol}^{-1})

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  5. Question 5

    9 May 2024 S1

    69
    A solution of non-volatile solute is obtained by dissolving 3.5 g in 100 g solvent and has boiling point elevation 0.35 K. Calculate the molar mass of solute (molal elevation constant =2.5 K kg mol−1=2.5\,K\,kg\,mol^{-1})

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  6. Question 6

    14 May 2024 S2

    75
    A solution of nonvolatile solute obtained by dissolving 15 g in 200 mL water has depression in freezing point 0.75 K. Calculate the molar mass if cryoscopic constant is 1.86 K kg mol−11.86\,\text{K kg mol}^{-1}.

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  7. Question 7

    25 Apr 2025 S1

    79
    A solution of 5 g nonvolatile solute in 50 g water decreases its freezing point by 0.2 K . Calculate the molar mass of solute if KfK_{f} of water is 1.86 K kg mol−11.86\text{ }K\text{ }kg{\text{ }mol}^{- 1}.

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  8. Question 8

    11 Apr 2026 S2

    22
    A solution of 50g of solute 'X' is dissolved in 150150 g of 'Y' solvent boils at 357.27357.27 K. What is the molar mass of solute? (Given KbK_b and boiling point pure solvent is 2.772.77 K kg/mol and 350.06350.06 K respectively.)

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  9. Question 9

    13 Apr 2026 S1

    20
    2 g nonelectrolyte solute when dissolved in 50 g water increases its boiling point by 0.13 K. Calculate the molar mass of solute if molal elevation constant of water is 0.52 K kg mol−1\mathrm{mol^{-1}}

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  10. Question 10

    17 Apr 2026 S1

    23
    Calculate the molar mass of nonvolatile solute when 4 g of it is dissolved in 100 g solvent that boils at 319.4 K [KbK_b = 2.4 K kg mol−1\mathrm{mol^{-1}}; B.P of pure solvent = 319 K]

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  11. Question 11

    14 May 2026 S2

    22
    A solution of 10.010.0 g of a nonvolatile, nonelectrolyte solute dissolved in 0.20.2 kg of benzene boils at 81.2∘C81.2^\circ\mathrm{C}. Calculate molar mass of the compound. (ebullioscopic constant for benzene =2.53= 2.53 K kg mol−1\mathrm{mol^{-1}} and boiling point of pure benzene =80.1∘C= 80.1^\circ\mathrm{C})

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  12. Question 12

    19 May 2026 S1

    25
    A solution containing 0.60.6 g nonelectrolyte solute in 3030 g water freezes at −0.6 ∘C-0.6\ ^\circ\mathrm{C}. Calculate the molar mass of solute if cryoscopic constant of water is 1.8 K kg mol−11.8\ \mathrm{K\ kg\ mol^{-1}}.

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  13. Question 13

    19 May 2026 S2

    23
    Addition of 0.6430.643 g of compound to 5050 ml of benzene (density of benzene =0.879= 0.879 g/ml) lowers the freezing point from 5.51∘C5.51^\circ\mathrm{C} to 5.03∘C5.03^\circ\mathrm{C}. If KfK_f for benzene is 5.125.12 K kg/mol. Calculate the molecular weight of a compound in gram?

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