[mrlucky0]

Which of the following measures of concentration is/are NOT affected by changes in temperature?

I. Molarity
II. Molality
III. Mole Fraction

My book says the correct answer is II. & III., Molality and Mole Fraction. I don't understand why it would be the case:

Say, you raise the temperature of the solution a bit and evaporate some solvent. Then wouldn't all three measures of concentrations necessarily increase? In other words, the quantity of solute (which remains the same) is in a smaller volume of solvent (that evaporated off) so Molarity, Molality, and Mole Fraction would all increase.

Or am I misinterpreting the question?

[Borek]

Question doesn't tell anything about evaporating solvent. It asks which of the measures won't change when the temperature changes without changing amount of the copounds in the mixture.

Does it change your understanding of the question?

[mrlucky0]

Does it change your understanding of the question?

Yes and No.

Here's what the solution says:

"Mole fraction is not affected by temperature. The mole fraction of a solution is the number of moles of solute divided by the number of moles of solution, and temperature changes do not change the number of moles in a sample. The molarity of a solution is the number of moles of solute per liter of solution; since density changes with temperature, the volume of the solution can change when the temperature changes. The molality of a solution is the number of moles of solute per kilogram of solvent; both of these variables are temperature-independent."

They acknowledged that molarity can change with temperature because, "volume of a solution can change with temperature." My question is, how could molarity  change (presumably by a decrease in the amount of solvent) without changing molality and mole fraction?

[sjb]

What is the definition of molarity?

[mrlucky0]

What is the definition of molarity?

Moles/Liter; So what I'm saying is that a change in volume (due to a change in temperature) will change the molarity.

[Borek]

Volume changes, mass doesn't change.