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Question:

The observed osmotic pressure for a 0.10 M solution of Fe(NH4)2(SO4)2 at 25°C is 10.8 atm. The expected and experimental (observed) values of Van't Hoff factor (i) will be respectively: [R=0.082 L atm K⁻¹ mol⁻¹]

5and3.42

3and5.42

5and4.42

4and4.00

Solution:

Fe(NH4)2(SO4)2 → 2NH₄⁺ + Fe²⁺ + 2SO₄²⁻
Expected value of i = 5
Now, observed van't hoff factor = π/MRT = 10.8/(0.10 × 0.082 × 298) = 4.42