Question

O.P. of solution can be measured by

• A. Photometer
• B. Osmometer
• C. Calorimeter
• D. Plasmolysis

Answer 1

Answer: (B)

Osmotic pressure is the hydrostatic pressure that is developed in a solution when the solution is separated by a semipermeable membrane from the pure solvent. It is a function of the amount of solute present in the solution. This is measured in Bars, Pascals, or Atmospheres.

The term was coined by Pfeffer. The instrument which is used to measure OP is called Osmometer or Berkeley and Hartley's Osmometer.
Numerically, Osmotic pressure ( $\pi $ , Pi) is equal to Solute potential ( $\text{ψ}$ _s, Psi) of a solution or Osmotic Potentials. But the major difference between Osmotic Pressure and Osmotic Potentials is that the former is positive, and the latter is negative. Thus, we may write like:
$\text{ψ}$ s = - $\text{\pi }$ .
Several factors control Osmotic Pressure:
1. Temperature: OP increases with the increase in temperature.
2. The concentration of solute in the solution: More the solute, more is the value of OP of the solution.
To calculate the OP of a solution, the formula which can be used as
$\text{\pi }$ = CST
C is the Molar concentration of solution; S is the Solution constant, which is 0.082, and is the Absolute temperature i.e., -273°K.