Molarity is a measure of the concentration of a solute in a solution. This molarity example problem shows the steps needed to calculate the molarity of a solution given the amount of solute and the desired volume of solution.

**Problem**

Calculate the molarity of a solution created by pouring 7.62 grams of MgCl_{2} into enough water to create 400 mL of solution.

**Solution**

The formula to calculate molarity is

In this case, the solute is 7.62 grams of MgCl_{2}. The formula needs the number of moles.

Using a periodic table, the molecular mass of MgCl_{2} is 95.21 grams/mol. Find the number of moles in 7.62 grams in MgCl_{2}.

moles MgCl_{2} = 0.08 moles

Molarity also needs to have the volume in liters, *not* milliliters.

The final volume of our solution is 400 mL, which is 0.4 L.

Plug this information into the formula

M = 0.2 moles/L or 0.2 M

**Answer**

The concentration of MgCl_{2} in the solution is 0.2 M.