Question

question 2
which of the following concentration units are temperature dependent?
a) molarity
b) molality
c) mass percent
d) mole fraction
e) none of the above
chem 1120: introduction to chemistry techniques iclickers
select an answer

Explanation:

• Molarity is defined as moles of solute per liter of solution ($M=\frac{n}{V}$). Since the volume ($V$) of a solution changes with temperature (due to thermal expansion or contraction), molarity is temperature - dependent.
• Molality is moles of solute per kilogram of solvent ($m=\frac{n}{m_{solvent}}$). Mass ($m_{solvent}$) is not affected by temperature, so molality is temperature - independent.
• Mass percent is $\text{Mass}\%=\frac{\text{mass of solute}}{\text{total mass of solution}}\times100$. Mass is not affected by temperature, so mass percent is temperature - independent.
• Mole fraction is $X=\frac{n_{solute}}{n_{solute} + n_{solvent}}$. Moles ($n$) are not affected by temperature (as they are based on amount of substance, not volume or physical dimensions that change with temperature), so mole fraction is temperature - independent.

Answer:

A. Molarity