In comparing the phase diagram for water with that of a solution of sugar in water, all of the following decrease except
a) the vapor pressure
b) the boiling point
c) the freezing point
d) the triple point
The way the problem is worded I don't know if we are taking H2O as the normal and saying the sugar solution will have those effects OR if we are taking sugar solution as normal as saying water will have those properties.
If we say we have water and compare that with sugar solution, the sugar solution will have a lower freezing point, a higher boiling point, and a lower vapor pressure. You can take that information and answer the question.
freezing point
To determine which of the given options decrease when comparing the phase diagram for water with a solution of sugar in water, we need to understand the effect of the solute (sugar) on the properties of the solvent (water).
In the case of a sugar-water solution, the presence of the solute (sugar) affects the behavior of the solvent (water). Specifically, it affects the boiling point, freezing point, and vapor pressure of the solution.
Let's discuss each option one by one:
a) Vapor pressure: The addition of a non-volatile solute like sugar decreases the vapor pressure of the solution compared to pure water. This is because the solute molecules occupy some of the space on the liquid surface, reducing the evaporation rate and vapor pressure. Therefore, option a) is correct: the vapor pressure decreases.
b) Boiling point: The presence of a solute raises the boiling point of the solution compared to pure water. This is due to the phenomenon known as boiling point elevation, where the solute particles lower the vapor pressure of the solution, requiring higher temperatures to achieve the boiling point. Therefore, option b) is incorrect: the boiling point increases.
c) Freezing point: The presence of a solute lowers the freezing point of the solution compared to pure water. This is due to the phenomenon known as freezing point depression, where the solute particles disrupt the formation of an ordered solid lattice, requiring lower temperatures for the solution to freeze. Therefore, option c) is incorrect: the freezing point decreases.
d) Triple point: The triple point is the temperature and pressure at which all three phases of a substance (solid, liquid, and gas) coexist in equilibrium. The addition of a solute does not affect the triple point since it is a characteristic property of the solvent, which is water in this case. Therefore, option d) is correct: the triple point does not change.
So, the correct answer is:
a) the vapor pressure.