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Question
Answer the following.
How molar mass of a solute is determined by osmotic pressure measurement?
Solution
1. For very dilute solutions, the osmotic pressure follows the equation,
`pi = ("n"_2 "RT")/"V"` ....(1)
2. If the mass of solute in V litres of a solution is W2 and its molar mass is
`"M"_2`, then `"n"_2 = "W"_2/"M"_2`
Substituting the value of n2 in equation (1), we get
`pi = ("W"_2 "RT")/("M"_2 "V")`
∴ `"M"_2 = ("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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