Question

At low concentrations, the statement that equimolal solutions under a given set of experimental conditions have equal osmotic pressure is true for
A. All solutions
B. Solutions of non-electrolytes only
C. Solutions of electrolytes only
D. None of these

Answer 1

Hint: The solutions will have equal osmotic pressure when the concentration of solutes same for all solutions or negligible. Now, as for different solutions, solute solubility is different (solute dissolves in different solutions to a different extent) due to this, volt off factor change and thus, osmotic pressure will alter. So, to get the same osmotic pressure, the volt off factor should be the same.

Complete Step by Step Answer:
Osmotic pressure (p) of any solution depends on volt off factor (i), the concentration of solvent (c), had constant (R) and absolute temperature (T) such as
\[p1\text{ }=\text{ }icRT\]

If all the solutions are at low concentration, means that a solution contains a very less number of solute particles or can say negligible then the osmotic pressure will be independent of concentration or can say the concentration of solutions act as a new constant like R.

Now osmotic pressure only depends on volt off factor (i) which gives an idea about the solubility of ions of solute (present in less amount) in the solution. If all the solutions contain only solute particles which are good electrolytes then all the solutes will get associated and dissociate into ions in the solutions. As association and dissociation will be different for different solutions and thus, the volt off factor will also get change and thus, osmotic pressure of all the solutions will also get different.

Now if we take solutions of non-electrolyte solutes then the solutes which are present in less amount do not get associated and dissociate into ions. Thus, it will not alter the volt off factor i and due to this osmotic pressure of all the solutions will remain the same.
\[p1=\text{ }cRT\text{ }=\text{ }p2\text{ }=\text{ }p3\] and so on \[\left( i\text{ }=\text{ }1 \right)\]
Thus, the correct option is B.

Additional information: Osmotic pressure is the force required to stop the osmosis process or it is the measure of the force with which the osmosis process occurs. Osmotic pressure is independent of gas constant as its value is fixed for all solutions and osmosis occurs at any particular absolute temperature.

Note: Osmotic pressure for all the solutions can be equal when the solution is dilute or less concentrated and solutes are non- electrolyte due to which solutes do not dissociate and do not affect the concentration of the solution. It is important to note that volt off factor is equal to 1 for non-electrolyte solutions. But for electrolyte solutions, they can take different values.