Ways of Expressing Concentration
We will examine four ways to express concentration in quantitative terms:
Mass percentage, mole fraction, molarity, and molality
1. Mass percentage
Mass % of component= mass of component in solution x 100
Total mass of solution
A commercial bleaching solution contains 3.62 mass% sodium
hypochlorite, NaOCl. What is the mass of NaOCl in a bottle containing
2.50 kg of bleaching solution?
2. Mole Fraction
Mole fraction = moles of component
total moles of all components
The symbol X is commonly used for mole fraction, with a subscript to
indicate the component of interest. For example, the mole fraction of NaCl
in a solution of NaCl is represented as XNaCl. Mole fractions have no units.
An aqueous solution of hydrochloric acid contains 36% HCl by mass.
Calculate the mole fraction of HCl in the solution.
3. Molarity
Molarity = moles of solute
liters of solution
What is the molarity of a solution made by diluting 35.0 mL of 9.00 M H2
SO4 to 0.500 L?
4. Molality
Molality = moles of solute
kilograms of solvent
A solution was prepared by dissolving 17.1 g of C12H22O11 in 125 g of
water. Find the molal concentration of this solution.