The boiling point of a solution will ______ and the vapor pressure will _______ with a(n)_____ in the amount of dissolved solute.
increase
decrease
increase
The boiling point of a solution will increase and the vapor pressure will decrease with an increase in the amount of dissolved solute.
To understand why this happens, we need to consider the concept of boiling point elevation and vapor pressure lowering, which are both colligative properties. Colligative properties depend on the number of particles present in a solution, regardless of their identity.
Boiling point elevation occurs because when a solute is dissolved in a solvent, the solute particles disrupt the solvent's normal boiling process. The solute particles "get in the way" of the solvent particles, making it harder for them to escape into the gas phase. Consequently, the boiling point of the solution is higher than that of the pure solvent.
Vapor pressure is a measure of the tendency of a liquid to evaporate. When a solute is dissolved in a solvent, the solute particles reduce the availability of the solvent particles at the surface of the solution, resulting in a lower vapor pressure. This means that it takes longer for the solvent to evaporate, as there are fewer solvent particles available to escape into the gas phase.
So, in summary:
- The boiling point of a solution increases because of boiling point elevation caused by the presence of solute particles.
- The vapor pressure of a solution decreases because of vapor pressure lowering caused by the reduced availability of solvent particles at the surface due to the presence of solute particles.