1. Percent by mass, mole fraction, molarity, and molality
Concentration Units
Percent by mass, mole fraction,
molarity, and molality

2. Percent by mASS PERCENT BY MASS = MASS OF SOLUTE X 100%
MASS OF SOLUTION
A sample of 0.892g of potassium chloride is dissolved in 54.6g of water.
What is percent by mass of KCl in the solution?
0.892g
Percent by mass of KCl =
X 100%
0.892g g
= 1.61%

3. Percent by mass, mole fraction, molarity, and molality
Concentration Units
Percent by mass, mole fraction,
molarity, and molality

4. Mole fraction (x) MOLE FRACTION OF COMPONENT A = XA = Moles of A
Σ all moles in solution
Your solution contains 5 moles of KCl and 15 moles of water.
What is the mole fraction of KCl?
5 moles KCl
XKCl =
= 0.25
5 moles KCl + 15 moles H2O
What is the mass percent of KCl?
74.55 g
5 mol KCl x
Mass percent of KCl =
1 mol KCl
= 58%
74.55 g
18.02 g
5 mol KCl x
15 mol H2O x +
1 mol KCl
1 mol H2O

5. Percent by mass, mole fraction, molarity, and molality
Concentration Units
Percent by mass, mole fraction,
molarity, and molality

6. Molarity and molality MOLARITY = M = MOLALITY = m = Moles of solute
Liters of solution
Kg of solvent
Calculate the molality of a sulfuric acid solution containing 24.4g of sulfuric acid in
198g of water. The molar mass of sulfuric acid is g/mol.
1 mol H2SO4
24.4 g H2SO4 x
mH2SO4 =
98.09 g
= 1.26m = 1.26 “molal”
0.198 kg H2O
What is the molarity of the solution? (d = 1.84 g/mL)
1 mL
Volume of solution =
(24.4g + 198g)
= mL
1.84g
mol H2SO4
Molarity = M =
= 2.06M = 2.06 “molar”
L solution