Question

Which formula is used to calculate osmotic pressure?

• A. \( \pi = CRT \)
• B. \( \pi = VRT \)
• C. \( \pi = PVT \)
• D. \( \pi = nRT \)

Hint:

Use the van't Hoff relation \( \pi V = nRT \) and replace \( n/V \) by molar concentration \( C \).

Answer 1

The Correct Option is A

Step 1: Osmotic pressure (\( \pi \)) is the colligative property equal to the extra pressure that must be applied to a solution to stop the inflow of solvent through a semipermeable membrane.
Step 2: The van't Hoff equation for a dilute solution is \( \pi V = nRT \), where \( n \) is moles of solute, \( V \) the volume of solution, \( R \) the gas constant and \( T \) the temperature.
Step 3: Rearranging, \( \pi = \dfrac{n}{V}RT \). Since molar concentration \( C = \dfrac{n}{V} \), this becomes \[ \boxed{\pi = CRT} \]
Step 4: So option (i) is correct. Option (iv) \( \pi = nRT \) is dimensionally wrong (it omits volume). Options (ii) and (iii) are meaningless combinations of symbols.