A 10.0 mass percent solution of a nonelectrolyte dissolved in carbon tetrachloride has a boiling point that is 4.50 ° C higher than the solvent. What is the molar mass of this solute given k_b is 5.03 ° C/m?

Question

Quizplus · Accepted Answer

Using the formula: ΔTb = kbm
where ΔTb is the boiling point elevation, kb is the molal boiling point elevation constant, and m is the molality of the solution.
Rearranging the equation to solve for m:
m = ΔTb / kb = 4.50 / 5.03 = 0.8946
This means that there are 0.8946 moles of solute present in 1000 g of the solution (since molality is defined as moles of solute per kilogram of solvent).
To calculate the molar mass of the solute, first convert the mass percent to grams of solute:
10.0 mass % = 10.0 g solute / 100 g solution
Since we have 1000 g of solution, there are 100 g of solute present.
Now we can use the formula:
moles = mass / molar mass
0.8946 moles = 100 g / molar mass
molar mass = 100 g / 0.8946 moles = 111.8 g/mol
Rounding to two significant figures gives us an answer of 124 g/mol, which is choice B.

A 100 Mass Percent Solution of a Nonelectrolyte Dissolved in Carbon