Chemistry 16.2

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Chemistry 16.2

© Copyright Pearson Prentice Hall

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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.

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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

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.

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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.

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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.

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Swirl the flask carefully to dissolve the solute.

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Fill the flask with water exactly to the 1-L mark.

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SAMPLE PROBLEM

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Practice Problems

Problem Solving 16.8 Solve Problem 8 with the help of an interactive guided tutorial.

for Sample Problem 16.2


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Sample Problem 16.3

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Sample Problem 16.3

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SAMPLE PROBLEM

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Sample Problem 16.3

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Practice Problems

ProblemSolving 16.11 Solve Problem 11 with the help of an interactive guided tutorial.



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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?


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Concentrations of Solutions> Making Dilutions

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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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.

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Making a Dilute Solution

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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.

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She then transfers the 20 mL to a 100-mL volumetric flask.

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Finally she carefully adds water to the mark to make 100 mL of solution.

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Volume-Measuring Devices

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Practice Problems

Problem Solving 16.12 Solve Problem 12 with the help of an interactive guided tutorial.


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Concentrations of Solutions> Percent Solutions

Percent Solutions

What are two ways to express the percent concentration of a solution?

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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.

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Concentration in Percent (Volume/Volume)

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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.

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SAMPLE PROBLEM

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Practice Problems

Practice Problems For Sample Problem 16.5

Problem-Solving 16.15 Solve Problem 15 with the help of an interactive guided tutorial.


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Concentration in Percent (Mass/Mass)

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Section Quiz

-or-Continue to: Launch:

Assess students’ understanding of the concepts in Section

16.2 Section Quiz.

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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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Chemistry 16.2

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