1

### AIPMT 2002

A solution contains non volatile solute of molecular mass M2. Which of the following can be used to calculate the molecular mass of solute in terms of osmotic pressure?
A
${M_2} = \left( {{{{m_2}} \over \pi }} \right)VRT$
B
${M_2} = \left( {{{{m_2}} \over V}} \right){{RT} \over \pi }$
C
${M_2} = \left( {{{{m_2}} \over V}} \right)\pi RT$
D
${M_2} = \left( {{{{m_2}} \over V}} \right){\pi \over {RT}}$

## Explanation

For dilute solution, the van’t Hoff equation is

$\pi = {n \over V}RT$

$\Rightarrow$ $\pi V = nRT$

$\Rightarrow$ $\pi V = {{{m_2}} \over M}RT$

$\Rightarrow$ ${M_2} = \left( {{{{m_2}} \over V}} \right){{RT} \over \pi }$
2

### AIPMT 2002

A solution containing components A and B folloes Raoult's law
A
A - B attraction force is greater than A - A and B - B
B
A - B attraction force is less than A - A and B - B
C
A - B attraction force remains same as A - A and B - B
D
volume of solution is different from sum of volume of solute and solvent.

## Explanation

These two components A and B follows the condition of Raoult’s law if the force of attraction between A and B is equal to the force of attraction between A and A or B and B.
3

### AIPMT 2001

Pure water can be obtained from sea water by
A
centrifugation
B
plasmolysis
C
reverse osmosis
D
sedimentation

## Explanation

The osmotic pressure of sea water is 25 atm at 15°C. When pressure greater than 26 atm is applied on sea water separated by a rigid semipermeable membrane. Pure water is obtained. This is also called desalination of sea water.
4

### AIPMT 2000

From the colligative properties of solution, which one is the best method for the determination of molecular weight of proteins and polymers?
A
Osmotic pressure
B
Lowering in vapour pressure
C
Lowering in freezing point
D
Elevation in boiling point

## Explanation

Molecular masses of polymers are best determined by osmotic pressure method . Firstly because other colligative properties give so low values that they cannot be measured accurately and secondly, osmotic pressure measurements can be made at room temperature and do not require heating which may change the nature of the polymer.