science

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Concentrations of Solutions
Water must be tested
continually to ensure that the
concentrations of contaminants
do not exceed established
limits. These contaminants
include metals, pesticides,
bacteria, and even the by-
products of water treatment.
You will learn how solution
concentrations are calculated.
(molarity; % v/v; %m/m; ppm)
16.2

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Concentrations of Solutions> Molarity
The concentration of a solution is a measure of
the amount of solute that is dissolved in a given
quantity of solvent.
• A dilute solution is one that contains a small
amount of solute.
• A concentrated solution contains a large
amount of solute.
16.2

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Concentrations of Solutions>
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16.2 Molarity
Molarity
How do you calculate the molarity of a
solution?

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Concentrations of Solutions> Molarity
Molarity (M) is the number of moles of
solute dissolved in one liter of solution.
To calculate the molarity of a solution,
divide the moles of solute by the volume
of the solution.
16.2

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Concentrations of Solutions> Molarity
To make a 0.5-molar
(0.5M) solution, first
add 0.5 mol of solute
to a 1-L volumetric
flask half filled with
distilled water.
16.2

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Concentrations of Solutions> Molarity
Swirl the flask
carefully to dissolve
the solute.
16.2
Fill the flask with
water exactly to the
1-L mark.

7. 16.2

8. 16.2

9. for Sample Problem 16.2

10. 16.3

11. Sample Problem 16.3
16.3

12. for Sample Problem 16.3

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Concentrations of Solutions>
16.2 Making Dilutions
Making Dilutions
What effect does dilution have on the
total moles of solute in a solution?
Diluting a solution reduces the number
of moles of solute per unit volume, but
the total number of moles of solute in
solution does not change.

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Concentrations of Solutions> Making Dilutions
The total number of moles of solute remains
unchanged upon dilution, so you can write this
equation.
M1 and V1 are the molarity and volume of the
initial solution, and M2 and V2 are the molarity
and volume of the diluted solution.
16.2

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Concentrations of Solutions> Making Dilutions
Making a Dilute Solution
16.2

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Concentrations of Solutions> Making Dilutions
To prepare 100 ml of 0.40M MgSO4 from a stock
solution of 2.0M MgSO4, a student first measures
20 mL of the stock solution with a 20-mL pipet.
16.2

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Concentrations of Solutions> Making Dilutions
She then transfers the 20 mL to a 100-mL
volumetric flask.
16.2

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Concentrations of Solutions> Making Dilutions
Finally she carefully adds water to the mark to
make 100 mL of solution.
16.2

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Concentrations of Solutions> Making Dilutions
Volume-Measuring Devices
16.2

20. 16.4

21. 16.4

22. for Sample Problem 16.4

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Concentrations of Solutions> Percent Solutions
Percent Solutions
What are two ways to express the
percent concentration of a solution?
The concentration of a solution in
percent can be expressed in two ways:
as the ratio of the volume of the solute
to the volume of the solution or as the
ratio of the mass of the solute to the
mass of the solution.
16.2

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Concentrations of Solutions> Percent Solutions
Concentration in Percent (Volume/Volume)
16.2

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Concentrations of Solutions> Percent Solutions
Isopropyl alcohol (2-propanol) is sold as a 91%
solution. This solution consist of 91 mL of
isopropyl alcohol mixed with enough water to
make 100 mL of solution.
16.2

26. 16.5

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SAMPLE PROBLEM
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16.5

28. Practice Problems For Sample Problem 16.5
for Sample Problem 16.5

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Concentrations of Solutions> Percent Solutions
Concentration in percent (mass/mass)
16.2

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Concentrations of Solutions> Parts per million
Concentration in parts per million (ppm)
(To complete)
16.2

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Section Quiz
-or-
Continue to: Launch:
Assess students’ understanding
of the concepts in Section
16.2 Section Quiz.
16.1.

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16.2 Section Quiz.
1. To make a 1.00M aqueous solution of NaCl,
58.4 g of NaCl are dissolved in
a. 1.00 liter of water.
b. enough water to make 1.00 liter of solution
c. 1.00 kg of water.
d. 100 mL of water.

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16.2 Section Quiz.
2. What mass of sodium iodide (NaI) is contained
in 250 mL of a 0.500M solution?
a. 150 g
b. 75.0 g
c. 18.7 g
d. 0.50 g

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16.2 Section Quiz.
3. Diluting a solution does NOT change which of
the following?
a. concentration
b. volume
c. milliliters of solvent
d. moles of solute

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16.2 Section Quiz.
4. In a 2000 g solution of glucose that is labeled
5.0% (m/m), the mass of water is
a. 2000 g.
b. 100 g.
c. 1995 g.
d. 1900 g.

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16.2 Section Quiz.
4. In a 2000 g solution of glucose that is labeled
4.0 ppm, the mass of glucose is
a. 2000 g.
b. 100 g.
c. 1995 g.
d. 0.0080 g.

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