After you preform your experiment, you determine that the Kf value for naphthalene is 6.89 °C/m . You are using 10g of naphthalene and added 1.0 g of your unknown. The the freezing point of the solvent decreased by 4.42 °C when the unknown was added. Knowing this information, determine the molar mass of the unknown.

Question

After you preform your experiment, you determine that the Kf value for naphthalene is 6.89 °C/m .  You are using 10g of naphthalene and added 1.0 g of your unknown.  The the freezing point of the solvent decreased by 4.42 °C when the unknown was added.  Knowing this information, determine the molar mass of the unknown.

DrBob222 · Answer

delta T = Kf*molality
You know delta T and Kf, solve for m.

molality = mols/kg solvent. You know m and kg solvent, solve for mols.

Then mols = grams/molar mass
You know mols and grams, solve for molar mass.