JEE Main · 2019 · Shift-IIeasySOL-104

Molal depression constant for a solvent is 4.0 K kg mol⁻¹. The depression in the freezing point of the solvent for 0.03…

Solutions · Class 12 · JEE Main Previous Year Question

Question

Molal depression constant for a solvent is 4.0 K kg mol⁻¹. The depression in the freezing point of the solvent for 0.03 mol kg⁻¹ solution of K2SO4\mathrm{K_2SO_4} is:

(Assume complete dissociation of the electrolyte)

Options
  1. a

    0.36 K

  2. b

    0.24 K

  3. c

    0.18 K

  4. d

    0.12 K

Correct Answera

0.36 K

Detailed Solution

Strategy:\n> Freezing point depression is calculated using ΔTf=iKfm\Delta T_f = i \cdot K_f \cdot m. Identify the van't Hoff factor for the completely dissociated salt.\n\nStep 1: Identify } i \text{ for } \ce{K2SO4} \text{\n\ceK2SO4>2K++SO42\ce{K2SO4 -> 2K+ + SO4^2-}\nTotal ions (nn) = 3. Since dissociation is complete, i=3i = 3.\n\nStep 2: Calculate } \Delta T_f \text{\nKf=4.0,m=0.03.K_f = 4.0, m = 0.03.\nΔTf=3times4.0times0.03=12times0.03=0.36textK\Delta T_f = 3 \\times 4.0 \\times 0.03 = 12 \\times 0.03 = 0.36\\text{ K}\n\ntextAnswer:(1)\boxed{\\text{Answer: (1)}}

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