A solution is made using 79.9 g of phenol (MM = 94.11 g/mol) and 90.0 g of acetone (MM = 58.08 g/mol). What is the molality of the phenol in the solution?

Question

A solution is made using 79.9 g of phenol (MM = 94.11 g/mol) and 90.0 g of acetone (MM = 58.08 g/mol). What is the molality of the phenol in the solution?

Answer 1

Molality (m) = moles of phenol / kg acetone

moles of phenol = 79.9 g phenol x 1 mol phenol / 94.11 g = 0.8490 mols phenol

kg acetone = 90.0 g x 1 kg / 1000 g = 0.0900 kg

Molality (m) = 0.8490 moles / 0.0900 kg = 9.43 m (to 3 sig. figs.)

(note: the molar mass of acetone is given but is not needed to solve this problem).