Osmosis And Reverse Osmosis

Question

The osmotic pressure of a 0.02 M solution of a non-electrolyte at 300 K is closest to which value? (Take R = 0.082 L·atm·K⁻¹·mol⁻¹)

RankGuru · Accepted Answer

Osmotic pressure is calculated using the van't Hoff equation: π = CRT, where C is the molar concentration, R is the gas constant, and T is the absolute temperature. For a non-electrolyte, the van't Hoff factor i = 1. Given: C = 0.02 mol/L, R = 0.082 L·atm·K⁻¹·mol⁻¹, T = 300 K. Therefore, π = 0.02 × 0.082 × 300 = 0.492 atm. Option 0.248 atm corresponds to using T = 150 K (half the given temperature), an arithmetic slip. Option 0.984 atm results from using C = 0.04 mol/L (doubling the concentration). Option 0.124 atm would require C = 0.005 mol/L, one-fourth of the given concentration. The van't Hoff equation for osmotic pressure has the same mathematical form as the ideal gas law, which is its physical origin — the partial pressure of the solute behaving like an ideal gas. Plausibility check: a small concentration (0.02 M) gives a small osmotic pressure (< 1 atm), which is physically sensible. This is a direct NCERT example from the Solutions chapter and is a staple JEE Main numerical question.

Osmosis And Reverse Osmosis

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