A solution of acetic acid, CH3COOH, has a concentration of 0.218 M and a density of 1.00 g mL-1. What is the molality of this solution?

Answer 1

0.218M means 0.218 mols CH3COOH/L solution.
g CH3COOH = 0.218 x molar mass = approx 13g but you should redo this and all of the other calculations that follow. I've estimated everything.
From density, mass = volume x density = 1000 mL x 1 g/mL = 1000 grams.
So 1000g = mass H2O + mass CH3COOH = mass H2O + 13 g or mass H2O = approx 1000-13 = about 987g.
m = molality = mols/kg solvent
m = 0.218mols/0.987 kg = ?

Answer 2

0.22