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Slide 1 of 46
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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Slide 2 of 46
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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>
Slide 3 of 46
16.2 Molarity
Molarity
How do you calculate the molarity of a solution?
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Slide 4 of 46
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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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Slide 5 of 46
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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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Slide 6 of 46
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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.
16.2
16.2
for Sample Problem 16.2
16.3
Sample Problem 16.3
16.3
for Sample Problem 16.3
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Slide 13 of 46
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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Slide 14 of 46
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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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Slide 15 of 46
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Concentrations of Solutions> Making Dilutions
Making a Dilute Solution
16.2
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Slide 16 of 46
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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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Slide 17 of 46
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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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Slide 18 of 46
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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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Slide 19 of 46
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Concentrations of Solutions> Making Dilutions
Volume-Measuring Devices
16.2
16.4
16.4
for Sample Problem 16.4
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Slide 23 of 46
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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Slide 24 of 46
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Concentrations of Solutions> Percent Solutions
Concentration in Percent (Volume/Volume)
16.2
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Slide 25 of 46
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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
16.5
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SAMPLE PROBLEM
Slide 27 of 46
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16.5
Practice Problems For Sample Problem 16.5
for Sample Problem 16.5
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Slide 29 of 46
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Concentrations of Solutions> Percent Solutions
Concentration in percent (mass/mass)
16.2
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Slide 30 of 46
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Concentrations of Solutions> Parts per million
Concentration in parts per million (ppm)
(To complete)
16.2
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Slide 31 of 46
Section Quiz
-or-Continue to: Launch:
Assess students’ understanding of the concepts in Section
16.2 Section Quiz.
16.1.
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Slide 32 of 46
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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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Slide 33 of 46
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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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Slide 34 of 46
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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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Slide 35 of 46
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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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Slide 36 of 46
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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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