SOLUTION CONCENTRATION
The concentration (c) of a solution refers to the ration of the quantity of solute to the quantity of
solution:
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Percentage Concentration
The concentration of solutions is sometimes expressed as percentages on consumer products.
Percent volume/volume
% V/V
Percent *weight/volume
% W/V
Percent *weight/weight
% W/W
% V/V = volume of solute
100 mL of solution
% W/V = mass of solute (g)
100 of solution (mL)
% W/W = mass of solute (g)
100 g of solution
Vinegar is 5% V/V of acetic
Hydrogen peroxide is sold as
Benzoyl peroxide is found in
acid, which means that
3% W/V, which means that
acne cream and is listed as 5%
there is ________ of acetic
there is ________ of hydrogen
W/W, which means there is
acid for every ___________
peroxide for every __________
_________ of benzoyl peroxide
of solution.
of solution.
for every _________ of cream.
*Should really be expressed as mass/volume or mass/mass - but consumer goods still use “weight” on
the packaging.
Example #1
Rubbing alcohol is commonly used as an antiseptic for small cuts. It is sold as 70% (v/v) solution of
isopropyl alcohol in water. What volume of isopropyl alcohol is used to make 500 mL of rubbing
alcohol?
Example #2
Many people use a solution of trisodium phosphate (TSP), to clean walls before putting up
wallpaper. The recommended concentration is 1.7% (W/V). What mass of TSP is needed to make
2.0 L of solution?
Very Low Concentrations
In environmental studies, we often encounter very small amounts of solute.
To give reasonable numbers to these tiny amounts we tend to use either parts per million (ppm),
parts per billion (ppb) or parts per trillion (ppt).
Concentration
1 ppm
1 ppb
1 ppt
Analogy
These concentrations are expressed as fractions, with the mass of the solute being divided by the
mass of solution:
Parts per million
ppm =
Parts per billion
Parts per trillion
mass of solute x 106 ppb = mass of solute x 109 ppt = mass of solute x 1012
mass of solution
mass of solution
mass of solution
Conversion factor:
Conversion factor:
Conversion factor:
Example #3
Health Canada’s guideline for the maximum mercury content in commercial fish is 0.5 ppm. When
a 1.6 kg salmon was tested, it was found to contain 0.6 mg of mercury? Would this salmon be safe
to eat?
Example #4
An environmental protection agency regulation sets the concentration limit for copper in drinking
water at 1.3 ppm. Calculate the mass of copper in 1.0 L of water at this concentration.
Your turn:
1.
A solution of hydrochloric acid was formed by dissolving 1.52 g of hydrogen chloride gas in
enough water to make 24.1 mL of solution. What is the concentration in percent (m/v) of the
solutions?
2.
At 25C, a saturated solution of carbon dioxide gas in water has a concentration of 0.145%
(m/v). What mass of carbon dioxide is present in 250 mL of the solution?
3.
60 mL of ethanol is diluted with water to a final volume of 400 mL. What is the percent by
volume of ethanol in the solution?
4.
Milk fat is present in milk. Whole milk usually contains about 5.0% milk fat by volume. If you
drink a glass of milk with a volume of 250 mL, what volume of milk fat have you consumed?
5.
Vinegar is sold as a 5% (v/v) solution of acetic acid in water. How much pure water should be
added to 15 mL of acetic acid to make a 5% (v/v) solution of acetic acid? Note: Assume that
when the water and acetic acid are mixed, the total volume of the solution is the sum of the
volumes of each.
6.
Water supplies with dissolved calcium carbonate greater than 500 mg/L are considered
unacceptable for most domestic purposes. Express this concentration in parts per million.
7.
Cadmium is a highly toxic metal. The average level of cadmium in the blood of Canadians is
about 0.35 ppb. At this level, what mass of cadmium would be present in 1.5 kg of blood?
Answers: (1) 6.31 % (2) 0.36 g (3) 15% (4) 12.5 mL (5) 285 mL (6) 500 ppm (7) 5.2 x 10 -7 g