Question

A solution of an unknown volatile nonelectrolyte was prepared by dissolving

0.250 g of the substance in 40.0 g of CCl4 (carbon tetrachloride). The boiling
point of this solution was 0.357oC higher than that of pure carbon
tetrachloride. Calculate the molar mass of the solute.
𝐾𝑏 (𝐶𝐶𝑙4)=5.02 °C/𝑚

Answer 1

Do this.

delta T = Kb*molality
You know delta and Kb from the problem. Substitute and solve for molality.
Then molality = m = moles/kg solvent. You now know m and kg solvent (0.0400) from the problem so solve for moles.
Finally, moles = grams/molar mass. You know moles and grams; solve for molar mass.
Post your work if you get stuck.