Concentration Measurement:
Percent and PPM
Mr. Shields
Regents Chemistry
U12 L03
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Percent Concentration (V/V)
The two “Percent” methods for measuring
Concentration are Volume/Volume (V/V) and Mass/Mass
(m/m).
Let’s look at the V/V method 1st:
The formula for % Concentration (V/V) is:
Percent (V/V) = Volume of solute
Volume of Solution
x 100
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Percent Concentration (V/V)
Using Percent (V/V) to specify Concentration is used when
BOTH the solute and solvent are liquids
Example: water + vinegar
(H20 + CH3COOH)
It also assumes no INTERACTION (i.e. reaction) between
The solute and the solvent.
And notice that we are dividing the volume of the SOLUTE
By the volume of the SOLUTION – not the other way around
Percent (V/V) = Volume of Solute x 100
Volume of Solution
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Percent Concentration (V/V)
V/V solution concentrations tells us what % of solute is
present in the solution. Doubling the amount of solute will
Not necessarily double the % V/V. As we add solute to the
solvent the volume of the solvent also increases.
% V/V = 3/9 = 33%
% V/V = 6/12 = 50%
How much solute and solvent is present in each?
AND REMEMBER ! It is essential to express both the
Solute and the solution volumes in the SAME UNITS.
For example Liters and Liters or Milliliters and Milliliters,
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Percent (V/V) Problem
27 ml of ethanol are dissolved in 270 ml of Octane.
What is the % Concentration of Ethanol?
% Conc. (V/V) = 27 ml x 100
(27 + 270)
=
9.1%
What is the concentration in % (V/V) if 1.5 ml of Vinegar
Is dissolved in 30 ml of water?
% conc. of vinegar (V/V) = 1.5 ml
(1.5 + 30)
x 100
= 4.76 %
Note: Vinegar bought at the store is about a 5% sol’n5
Percent Concentration (m/m)
Percent Concentration by mass, % (m/m), is calculated very
Much like the % (v/v) method:
Percent (m/m) = Mass of solute
Mass of Solution
x 100
NOTE it’s the mass of the Solution and NOT the just the
Solvent.
As in v/v calculations the total
solution is equal to the sum of
Both the Solute and the Solvent
mass + mass mass
=
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Percent (m/m) Problem
1) What is the % Concentration (m/m) of I2 if 16.7g of I2
Are dissolved in 250g of ethanol?
% Conc. (m/m) = 16.7g
x 100
(16.7g + 250g)
= 6.26%
2) 24g of AgNO3 were dissolved in 125ml of water. What
Is the % concentration (m/m) of AgNO3 in solution?
Desity of H2O = 1g/ml; the mass of the water = 125g
Conc. of AgNO3 (m/m) = 24g
x 100
(24 + 125)
= 16.1%
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PPM
The last method of expressing sol’n concentrations
Quantitatively is PARTS PER MILLION (i.e. ppm)
This method is used extensively in the
Environmental Field. Why is this the case?
It’s a method that allows one to easily comprehend the
Concentration of extremely small amounts of solute in
Solvent.
So we might find for example that a sample of drinking
Water contains 3.2 ppm of Arsenic and compare that to
the allowable levels of As in drinking water (0.05 ppm)
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PPM
If the allowable limits of As in drinking water is 0.05 ppm,
What does this mean in terms of concentration?
- First, 1 ppm means 1 part in 1 million (106) parts
So, if the acceptable level of As is 0.05 ppm
then for every 5 Molecules of As molecules
allowed in drinking water there must be
100,000,000 (108) molecules of water.
Expressed another way we could say…
- for every 5g of As there must be 100,000,000g of H20!
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PPM Calculations
How do we calculate ppm? We’ll use this equation…
ppm of solute = Mass of Solute x 106
Mass of Solution
Notice that again we are dealing with the TOTAL mass
Of the solution.
Let’s look at an example…
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PPM Calculations
A 6.5g sample of well water is found to contain
3.5 x 10-6g of Pb+2. What is the concentration of lead
In the well water in ppm?
PPM Lead = mass of the solute x
mass of the solution
106
PPM Lead = 3.5 x 10-6g x 106
6.5g
Is this the total mass?
PPM Lead = 0.538 ppm
Why can we use it?
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PPM Calculations
What is the concentration in ppm of NaCl in water if
1.2g is dissolved in 240 ml of water?
PPM NaCl = mass of the solute x
mass of the solution
PPM NaCl =
106
1.2g
x 106 = 4975.1 ppm
(1.2 +240)g
The salinity of sea water is about
35,000 ppm
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PPM Calculations
What if we hadn’t added in the 1.2g of NaCl to the
Mass of solvent (240g). Would it have made a difference?
Let’s check it out …
PPM NaCl = mass of the solute x
mass of the solution
PPM NaCl =
1.2g
240g
106
x 106 = 5000 ppm
Mass of solvent ONLY
YES! It would have made a difference 5000ppm vs 4975ppm
So always add in the mass of the Solute to the solvent
if it is a Significant amount
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PPM Calculations
What if we had only added in 1.2 mg of NaCl to 240 ml
Of water. Does it make much difference if we add the
Mass of the salt to the solvent?
Calculate it both ways and see …
PPM NaCl = 0.0012g
(0.0012 + 240)g
x 106 = 4.999975ppm
PPM NaCl =
x 106 = 5.000000ppm
0.0012g
240g
Are these two numbers significantly different?
No, not really! So here we could have ignored the mass
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Of the salt
Global Warming is blamed on the increase in CO2
Levels in the atmosphere.
A) How much did CO2 increase in both ppm and %
between 1957 and 2000?
B) In 2000 what
Was the
Percent by
Volume of CO2
In the atmosphere?
54 ppm increase or
16.98% increase in CO2
(372-318)/318 x 100
372 X 100 =
106
O.037%
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