Question

Calculate the molarity of a solution containing 20.7 g of potassium carbonate dissolved in 500 mL of solution.

Answer 1

This is how you crack it up;

Molarity=number of moles/volume of solution

since we do not have the number of moles, but instead we have the mass

We say: Number of moles= mass/molar mass

∴No of moles=20.7g/138.205g/mol

                     = 0.149mol

∴molarity=0.149mol/500mL

molarity= 0.000298mol/mL or (0.000298M)