What is the molality of an aqueous solution of potassium hydroxide (KOH, 56.106 g/mol) if the molarity of the solution is 6.57 mol/L?

Question

Be sure to read the graph carefully. Enter your value using three significant figures.

Answer 1

You need the density of the KOH solution in order to go from molarity to molality.

There are formulas that connect the two. I prefer picking a basis of 1 liter of solution:

1) Find the mass of solution from density of solution times 1 liter

2) Find the mass of KOH in a liter of solution by multiplying molarity by 1 liter and the molar mass.

3) Find the mass of water = mass of solution - mass of KOH, and convert to kilograms

4) Divide the moles of KOH by the kg of water = molality

molality = 1000 Molarity / (1000ρ_soln - (Molarity) (Molar Mass KOH)) with the density in g/ml, the molarity in moles/liter, the molar mass in g/mole.

Hope that helps.