Calculating Molarity

Known                                                         Unknown

Mass of Solute                                    Solution Concentration

Molar Mass of Solute

Volume of Solution

 

Use molar mass to calculate the number of moles in your solute.

(7.54g FeCl2) 1mol FeCl2 / 126.753g FeCl2

7.54 X 0.00788936

0.0594 mol FeCl2

Use the conversion factor (1L / 1,000 ml) to convert the volume of H2O from ml to L.

(85 ml Solution)(1L / 1,000 ml)

85 X 0.001

0.085 Liters Solution

Substitute known values into the equation for molarity and solve.

Molarity = Moles of Solute / Liters of Solution

Molarity = 0.0954 mol FeCl2 / 0.085 L Solution

0.698 mol FeCl2 / 1 L Solution

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