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Question
For a very dilute solution, the osmotic pressure is given by π = n2RT/V where V is the volume in L containing n2 moles of nonvolatile solute. Establish the equation for molar mass of solute.
Solution
For very dilute solutions, the osmotic pressure follows the equation,
`pi = ("n"_2 "RT")/"V"` ....(1)
If the mass of solute in V litres of solution is W2 and its molar mass is
M2, then n2 = `"W"_2/"M"_2`
Substituting the value of n2 in equation (1), we get
`pi = "W"_2/"M"_2 "RT"/"V"`
∴ M2 = `("W"_2"RT")/(pi"V")`
This formula can be used for the calculation of molar mass of a nonionic solute (i.e., nonelectrolyte), by osmotic pressure measurement.
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