Question

Question-2 The molecular weight of
potassium sulphate determined by
measuring the osmotic pressure of its aqueous solution will be
a)Double the theoretical value
b)Same as the theoretical value
c)Half the theoretical value
d)One third the theoretical value​

Answer 1

Answer:

Sorry I don't know that

...........

Answer 2

The correct answer is option (d).

Explanation:

When Van't Hoff factor is not considered, we write:

$\pi=CRT$

Here, $\pi$ is osmotic pressure, R is universal gas constant and T is     temperature.

∴ $C=\frac{\pi}{RT}$

$Concentration =\frac{no \hspace2 of \hspace2 moles }{total \hspace2 volume}= \frac{n}{v}$

So, we have:

$\frac{n}{v}={\pi}{RT}\\\frac{W}{M.V}=\frac{\pi}{RT}\\M=(\frac{W}{V}).(\frac{RT}{\pi})$

But we know:

$K_2SO_4 \rightarrow 2K^++SO_{4}^{2-}$

Van't Hoff factor (i) = $\frac{total \hspace2 no \hspace2 of \hspace2 ions \hspace2 after \hspace2 reaction}{total \hspace2 no \hspace2 of \hspace2 ions \hspace2 before \hspace2 reaction}=\frac{3}{1}$

∴ i =3

So,

$\pi=iCRT\\\pi= 3CRT \\C=\frac{\pi}{3RT}$

Since,

$\frac{n'}{V}=\frac{\pi}{3RT}\\\frac{W}{M.V}=\frac{\pi}{3RT} \\M'=(\frac{W}{V})(\frac{3RT}{\pi})$

So, we get M' = 3M

Or, $M=\frac{1}{3}M'$

Hence, molecular  weight of  potassium sulphate determined by

measuring the osmotic pressure of its aqueous solution will be  one third of the theoretical value.