SOLUTIONS

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SOLUTIONS
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). Lets look at the V/V method
1st
The formula for Concentration (V/V)
is Percent (V/V) Volume of solute x
100 Volume of Solution
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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 9.1 (27
270)
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 x 100 4.76
(1.5 30)
Note Vinegar bought at the store is about a 5
soln
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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 x 100
Mass of Solution NOTE its 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
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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
6.26 (16.7g 250g)
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
16.1 (24 125)
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PPM
The last method of expressing soln
concentrations Quantitatively is PARTS PER
MILLION (i.e. ppm)
This method is used extensively in
the Environmental Field. Why is this the
case? Its 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? Well 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. Lets 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 Pb2. What is the
concentration of lead In the well water in ppm?
PPM Lead mass of the solute x 106 mass
of the solution PPM Lead 3.5 x 10-6g x
106 6.5g PPM Lead 0.538 ppm
Is this the total mass? 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 106 mass
of the solution PPM NaCl 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 hadnt added in the 1.2g of NaCl to
the Mass of solvent (240g). Would it have made a
difference? Lets check it out
PPM NaCl mass of the solute x 106 mass
of the solution PPM NaCl 1.2g x
106 5000 ppm 240g
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 x 106
4.999975ppm (0.0012 240)g PPM NaCl
0.0012g x 106 5.000000ppm
240g Are these two numbers significantly
different? No, not really! So here we could have
ignored the mass Of the salt
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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?
54 ppm increase or
B) In 2000 what Was the Percent by Volume of
CO2 In the atmosphere?
16.98 increase in CO2
(372-318)/318 x 100
372 X 100 106
O.037