Concentration

8-4. Know how to calculate the concentration of a solute in
terms of grams per liter, molarity, parts per million and
percent composition. (CSS: 6d)

Concentration of a Solution
• Concentration is a
measure of how much
solute is dissolved in a
given amount of
solution.
• High concentration –
large amounts of solute
in the solution
• Low concentration –
small amounts of solute
in the solution

Calculating the Concentration of a
Solution
• Concentration can be
expressed in a variety of
ways:
• Molarity (M)
• Grams per Liter (g/L)
• % Composition
• Parts per million (ppm)
• Conversion Factors to
know:
• 1 gram H2O = 1 mL H2O
• 1 L = 1000 mL
Concentrat ion
AmountofSolutue
AmountofSolution

Molarity (M)
• Most commonly used in acid/base
chemistry
M
MolesofSolute
LitersofSolution
• Example: Calculate the molarity of
20.0 grams of NaOH in 100.0 grams
of H2O.
• Given:
20.0 g NaOH
100.0 g H2O
• Solve:
1. Convert grams NaOH to moles
NaOH
1molNaOH
20.0gNaOH 0. 500molNaOH
40gNaOH
2. Convert grams H2O to Liter H2O
1mL
1L
100.0gH2O
0. 1000 L
1gH O 1000 mL
3. Divide moles NaOH by Liters H2O
0.500 molNaOH
M 5. 00M
0.1000 L
• Answer: 5.00 M
2

Grams per Liter (g/L)
• Most commonly used to
express solubility
GramsperLiter
GramsofSolute
LitersofSolution
• Example: Calculate the grams
per liter of 20.0 grams of
NaOH in 100.0 mL of H2O.
• Given:
20.0 g NaOH
100.0 g H2O
• Solve:
1. Convert mL H2O to Liters
H2O
1L
100.0mL 0. 1000 L
1000 mL
2. Divide grams NaOH by Liters
H2O
20.0gNaOH
GramsperLi ter
200. g / L
0.1000 L
• Answer: 200. g/L

Percent Composition (%)
• The ratio of one part
solute to one hundred
parts solution
GramsofSolute
% Composition
x100
GramsofSolution
• Example: Calculate the
percent composition of
20.0 grams of NaOH in
100.0 grams of H2O.
• Given:
20.0 g NaOH
100.0 g H2O
• Solve:
1. Divide grams NaOH by
Grams H2O
20.0gNaOH
PercentCom position
x100
20.0%
NaOH
100.0gH O
2
• Answer: 20.0 % NaOH

Parts per Million (ppm)
• Used to describe the
concentration of very
dilute solutions.
• Most common unit for
reporting
environmental
pollutants
ppm
GramsofSolute 6
x10
GramsofSolution
• Example: Calculate the
parts per million of 0.020
grams of NaOH in 100.0
grams of H2O.
• Given:
20.0 g NaOH
100.0 g H2O
• Solve:
1. Divide grams NaOH by
Grams H2O
0.020
gNaOH 6
PartsPerMillion
x10
200 ppm
100.0 gH O
2
• Answer: 2000 ppm

What’s in your drinking water?
National Primary Drinking Water Standards as of 10/03
Contaminant
Parts per
Million (ppm)
Potential Health Effects from
Ingestion of Water
Arsenic 0.010
Skin damage or problems with circulatory
systems, and may have increased
risk of getting cancer
Asbestos (fibers >10
micrometers)
7 (million
fibers per
Liter)
Increased risk of developing benign
intestinal polyps
Carbon
tetrachloride
0.005
Liver problems; increased risk of cancer
Lead 0.015
Infants and children: Delays in physical
or mental development; children could
show slight deficits in attention span
and learning abilities; Adults: Kidney
problems; high blood pressure
Mercury (inorganic) 0.002
Kidney damage
Source: US EPA. Water On Tap: What You Need To Know. Modified 12/14/2004. EPA. 3/13/2008.
http://www.epa.gov/safewater/wot/pdfs/book_waterontap_full.pdf