What is the molarity of potassium fluoride?

Question

An aqueous solution of potassium fluoride is prepared by dissolving 3.67 g of potassium fluoride in 8.03×10² g of water. The density of the solution is 1.24 g mL^-1.

Determine the molarity (in mol/L) of potassium fluoride in the solution.

Answer 1

By definition, molarity is moles of solute (KF) per liter of solution.

First, we calculate moles of KF, using a molar mass of KF = 58.1 g/mol

3.67 g x 1 mol/58.1 g = 0.0632 moles

Next we find the volume of the solution using the mass of solution and the density

mass of solution = 3.67 g + 803 g = 806.67g

volume = 806.67 g x 1 ml/1.24 g = 650.5 ml = 0.6505 L

Molarity (M) = moles /L = 0.0632 mol/0.6505 L = 0.0972 M (3 sig figs)