calculate molality using densities

Question

A 0.160 M aqueous solution has a density of 8.86 g/ml. The solute's molecular weight is 299.49 g/ml. The density of water is 1.00 g/ml. Calculate the molality of this solution.

Answer 1

So, molality is defined as moles of solute per kg of solvent.

We will first find the moles of solute, then g of solute and then the kg of solvent.

If we have 1 L of solution, we have 0.160 moles of solute and we have 8860 g of solution (8.86 g/ml x 1000 ml)

mass of solute = 0.160 moles x 299.49 g/mol = 47.92 g of solute

mass of H2O = 8860 g - 47.92 g = 8812.08 g H2O = 8.812 kg H2O

molality = 0.160 moles / 8.812 kg = 0.01816 m