Q7 / 90 · JEE Main 2014 (19 Apr Online) · Chemistry

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- mol-1)

  • A
    4 and 4.00
  • B
    3 and 5.42
  • Correct answer
    C
    5 and 4.42
  • D
    5 and 3.42

Solution

π = i C R T.

1 0 . 8 = i × 0 . 1 0 × 0 . 0 8 2 × 2 9 8

i = 1 0 . 8 0 . 1 0 × 0 . 0 8 2 × 2 9 8 = 1 0 . 8 2 . 4 4 3 6   = 1 0 . 8 2 . 4 4 3 8

= 4.42 (experimental value)

FeSO 4 . NH 4 2 0 · 1 M SO 4 ⟶ Fe aq 2 + 0 1 M + 2 SO 4 aq 2 - 0 · 2 M + 2 NH 4 aq + 0 · 2 M

i (expected) = 0 · 5 M 0 · 1 M = 5

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

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