Subject:Chemistry
What is the difference between seawater and pure water in terms of osmotic pressure and vapour pressure?
Is this a question about St. Teresas College or physics? You decide.
In terms of osmotic pressure and vapor pressure, there are significant differences between seawater and pure water.
Osmotic pressure is the pressure required to prevent the flow of solvent through a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration. It is directly related to the concentration of solute particles in a solution.
In seawater, the main solute particles are various dissolved salts, such as sodium chloride, magnesium chloride, and calcium chloride. These salts increase the concentration of solute particles in seawater, leading to an elevated osmotic pressure compared to pure water. Osmosis is the process where water molecules move from an area of low solute concentration to an area of high solute concentration. Due to the high salt content in seawater, it has a higher osmotic pressure compared to pure water.
Vapor pressure, on the other hand, is the pressure exerted by the vapor molecules when a liquid is in dynamic equilibrium with its vapor phase. It is related to the escape of molecules from the liquid phase into the gas phase.
In pure water, the vapor pressure is influenced by temperature and humidity. At any given temperature, pure water has a specific vapor pressure that depends solely on the temperature. On the other hand, seawater has a reduced vapor pressure compared to pure water at the same temperature, primarily due to the presence of dissolved salts. The dissolved salts in seawater lower the vapor pressure by interfering with the escape of water molecules into the gas phase. This is why it takes longer for seawater to evaporate compared to pure water.
To summarize, seawater has a higher osmotic pressure compared to pure water due to the elevated concentration of salts. In terms of vapor pressure, seawater has a lower vapor pressure compared to pure water, primarily due to the presence of dissolved salts.