Calculate the molality of an aqueous solution that is 20.1% by mass calcium chloride. you might need to know that the density is 1.20 g/ml

The molarity of an aqueous solution that is 20.1 % by mass calcium chloride is 2.755 M

Number of moles = Molarity x Volume

In this case;

Assuming the sample of solution is 100.0 g by mass

Mass of the solute = 20.1/100 x (100 g)

                               = 20.1 g

Mass of solution = mass of solute + mass of solvent

Mass of solvent = 100 g - 20.1 g

                          = 79.9 g

Density = 1.2 g/ml

But; volume = mass/density

                    = 78.9 g/1.2 g/ml

                     = 65.75 ml  or 0.06575 L

Mass of solute = 20.1 g

But 1 mole CaCl2 = 110.98 g/mol

Therefore;

Number of moles = 20.1 g/ 110.98 g/mol

                             = 0.1811 moles

Molarity = Number of moles/ Volume in L

             = 0.1811 moles/ 0.06575 L

             = 2.755 Mole/Liter

             = 2.755 M

Keywords: Molarity, Moles, Volume

Level: High School

Subject: Chemistry

Chapter: Mole and stoichiometry equations

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