16.2 Concentration of Solutions
Learning Objectives
Solve problems involving the molarity of a
solution
 Understand dilution and how to do
dilution calculations
 Define and calculate percent by volume
and percent by mass solutions

Molarity (M)
Molarity (M) is the most common form of
expressing solution concentration
 Based on the total solution volume

moles of solute mol
M

liters of solution
L
Molarity assumption
If someone tells you that you
have a 5.0 M solution you
can assume this:
5 moles solute
1 liter solution
Example of Molarity (M) calculation
Calculate the molarity of a solution that contains 5.8g KCl
in 550mL of solution.
Solution: 5.8g KCl x 1 mol KCl = 0.078 mol KCl
74.55g KCl
0.078 mol KCl =
0.55 L solution
Answer: 0.14M
Making Dilutions
Most solutions are stored as concentrated
stock solutions
 Fresh solution made using dilution

M1V1  M 2V2
Visualizing a Dilution
Dilution
Add Solvent
Moles of solute
before dilution (i)
=
Moles of solute
after dilution (f)
MiVi
=
MfVf
Dilution Calculation
How many mL of aqueous 2.00 M
MgSO4 solution must be diluted
with water to prepare 100.0 mL
of aqueous 0.400 M MgSO4?
M1= 2.00 M MgSO4 New Solution
M2 = 0.400 M MgSO4
V2 = 100.0 mL of 0.400 M MgSO4
V1 = ?? mL of 2.00 M MgSO4
Stock Solution
M1V1 = M2V2
Solve for V1
V1= M2V2
M1
V1=(0.400M)(100.0mL)
(2.00M)
V1= 20.0 mL (so 20.0 mL of
stock solution will be
measured and diluted with
80.0 mL of water)
Percent Solutions
volsolute (mL)
% (v/v)
100
volsolution(mL)
mass solute (g)
% (m/v)
100
volsolution(mL)
mass solute (g)
% (m/m)
100
mass solution(g)
Mass Percent
% = mass solute x 100
mass solution
Assumptions you can make:
A 5.0% solution =
5g solute
100g solution
Mass Percent Calculation
What is the mass percent of 500g of water
containing 6.50g of copper sulfate?
Solution:
6.50 CuSO4 x 100% =
(500g +6.50g)
solution
Answer: 1.28 %
Parts per Million (ppm)
Parts per million (ppm) is a ratio of parts of a
solute to one million parts of a solution. Usually it
is used when describing amount of contaminants
in water.
What is the ppm of copper sulfate if you have a
solution of 500g of water containing 6.50g of
copper sulfate?
Solution:
6.50 CuSO4 x 106 =12833(12800 ppm)
(500g + 6.50g)