How does the osmotic pressure of an aqueous solution change as evaporation occurs?
pi = MRT.
If evaporation occurs, what happens to the volume? decreases? If the volume decreases, what happens to the molarity? If M goes up, pi goes up. If molarity goes down, pi goes down.
To understand how the osmotic pressure of an aqueous solution changes as evaporation occurs, we need to first understand what osmotic pressure is and what factors affect it.
Osmotic pressure is the pressure needed to prevent the net movement of solvent molecules through a semipermeable membrane into a solution. It is directly related to the concentration of solute particles in the solution.
During evaporation, only the solvent (in this case, water) molecules escape the solution, leaving the solute particles behind. As a result, the concentration of the solute in the solution increases over time due to the loss of water.
According to the van't Hoff equation, osmotic pressure (π) is directly proportional to the concentration (C) of solute particles:
π = i * C * R * T
where:
- π is the osmotic pressure
- i is the van't Hoff factor (the number of particles per solute molecule or formula unit)
- C is the concentration of solute particles
- R is the ideal gas constant
- T is the absolute temperature
As the concentration of solute particles increases, the osmotic pressure also increases. Therefore, as evaporation occurs and water is lost from the solution, the concentration of solute particles increases, leading to an increase in osmotic pressure.
It's worth noting that the increase in osmotic pressure due to evaporation is dependent on the nature and amount of solute present in the original aqueous solution. Different solutes have different effect on osmotic pressure.