Transcript 4. Solution Concentrations

General, Organic, and
Biological Chemistry
Fourth Edition
Karen Timberlake
Chapter 8
Solutions
8.4
Solution Concentration
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Lectures
Concentration
The concentration of a solution
 is the amount of solute dissolved in a specific amount
of solution.
 can be represented as
mass percent,
volume percent,
mass/volume percent, or
molarity.
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Chapter 8, Section 4
2
Mass Percent Concentration
 Mass percent (m/m) concentration is the grams of the
solute in exactly 100 g of solution (mass solute + mass
solvent).


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Chapter 8, Section 4
3
Calculating Mass Percent
Suppose we prepared a solution by mixing 8.00 g of KCl
(solute) with 42.00 g of water (solvent).
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Chapter 8, Section 4
4
Mass of Solution
When water is added to 8.00 g of KCl to form 50.00 g
of KCl solution, the mass percent concentration is
16.0% (m/m).
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Chapter 8, Section 4
5
Guide to Calculating Solution
Concentration
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Chapter 8, Section 4
6
Learning Check
A solution is prepared with 15.0 g of Na2CO3 and 235 g
of H2O. What is the mass percent (m/m) of Na2CO3 in the
solution?
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Chapter 8, Section 4
7
Solution
A solution is prepared with 15.0 g of Na2CO3 and 235 g
of H2O. What is the mass percent (m/m) of Na2CO3 in
the solution?
Step 1 Determine the quantities of solute and
solution.
Analyze the Problem.
Quantity
of Solute Quantity of Solution
Concentration
15.0 g
Na2CO3
? g Na2CO3/100 g
Na2CO3 solution
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15.0 g Na2CO3
+ 235 g H2O = 250 g
Na2CO3 solution
Chapter 8, Section 4
Type of
Solution
Problem
mass
percent
(m/m)
8
Solution
A solution is prepared with 15.0 g of Na2CO3 and 235 g
of H2O. What is the mass percent (m/m) of Na2CO3 in
the solution?
Step 2 Write the concentration expression.
Step 3 Substitute solute and solution quantities into
the expression and calculate.
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Chapter 8, Section 4
9
Volume Percent
The volume percent (v/v) is
 percent by volume of solute (liquid) in a solution, and

A 7% (v/v) solution contains 7 mL of solute per 100 mL
of solution.
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Chapter 8, Section 4
10
Learning Check
A bottle contains 59 mL of lemon extract solution. If the
solution contains 49 mL of alcohol, what is the volume
percent (v/v) of the alcohol in the extract solution?
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Chapter 8, Section 4
11
Solution
A bottle contains 59 mL of lemon extract solution. If the
solution contains 49 mL of alcohol, what is the volume
percent (v/v) of the alcohol in the extract solution?
Step 1 Determine the quantities of solute and solution.
Analyze the Problem.
Quantity
of Solute Quantity of Solution
Concentration
49 mL
alcohol
? mL alcohol/100
mL solution
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59 mL extract solution
Chapter 8, Section 4
Type of
Solution
Problem
volume
percent
(v/v)
12
Solution
A bottle contains 59 mL of lemon extract and 49 mL of
alcohol, what is the volume percent (v/v) of the alcohol in
the extract solution?
Step 2 Write the concentration expression.
Step 3 Substitute solute and solution quantities into
the expression and calculate.
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Chapter 8, Section 4
13
Mass/Volume Percent
 The mass/volume percent (m/v) is widely used for
preparation of intravenous solutions and medications.

 A 5% mass/volume percent solution contains 5 grams of
solute per 100 mL of solution.
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Chapter 8, Section 4
14
Preparation of a Solution:
Mass/Volume Percent
Water is added to 5.0 g of KI to make 250 mL of KI solution. The
mass/volume percent of the solution is 2.0% (m/v) KI solution.
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Chapter 8, Section 4
15
Molarity, (Moles/L)
Concentrations are frequently measured using molarity
(M), a concentration that states the number of moles of
solute in exactly 1 liter of solution.
If 2.0 moles of NaCl are dissolved in enough water to
prepare 1.0 L of solution, the resulting NaCl solution
has a molarity of 2.0 M.
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Chapter 8, Section 4
16
Molarity, (moles/L)
A solution of 2.0 moles of NaCl and water added to the
1-L mark is a 2.0 M NaCl solution.
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Chapter 8, Section 4
17
Learning Check
What is the molarity of a 0.350 L solution that contains
46 g of KCl?
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Chapter 8, Section 4
18
Solution
What is the molarity of a 0.350 L solution that contains
46 g of KCl?
Step 1 Determine the quantities of solute and
solution.
Analyze the Problem.
Quantity
of Solute Quantity of Solution Concentration
Type of
Solution
Problem
46 g of
KCl
Molarity
(M)
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0.350 L KCl solution
? M of KCl solution
or (? moles KCl/1 L
solution)
Chapter 8, Section 4
19
Solution
What is the molarity of a 0.350 L solution that contains
46 g of KCl?
Step 1 Determine the quantities of solute and
solution.
1 mole of KCl = 74.6 g of KCl
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Chapter 8, Section 4
20
Solution
What is the molarity of a 0.350 L solution that contains
46 g of KCl?
Step 2 Write the concentration expression.
Step 3 Substitute solute and solution quantities into
the expression and calculate.
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Chapter 8, Section 4
21
Summary of Concentration
Expressions
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Chapter 8, Section 4
22
Using Concentrations as
Conversion Factors
The value of 100 in the denominator of a percent
expression is an exact number. Examples of
conversion factors from concentrations are:
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Chapter 8, Section 4
23
Learning Check
Write two conversion factors for each solution.
1. 8.50% (m/m) NaOH
2. 4.8% (m/v) HCl
3. 3.4 M NaOH
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Chapter 8, Section 4
24
Solution
1. 8.50% (m/m) NaOH
2. 4.8% (m/v) HCl
3. 3.4 M NaOH
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Chapter 8, Section 4
25
Guide to Using Concentration to
Calculate Mass or Volume
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Chapter 8, Section 4
26
Learning Check
How many grams of NaCl are needed to prepare 225 g
of a 10.0% (m/m) NaCl solution?
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Chapter 8, Section 4
27
Solution
How many grams of NaCl are needed to prepare 225 g
of a 10.0% (m/m) NaCl solution?
Step 1 State the given and needed quantities.
Analyze the Problem.
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Given
Need
225 g NaCl solution
10.0% (m/m) NaCl solution
? grams NaCl
Chapter 8, Section 4
28
Solution
How many grams of NaCl are needed to prepare 225 g
of a 10.0% (m/m) NaCl solution?
Step 2 Write a plan to calculate the mass or
volume.
g of solution
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% (m/m) factor
Chapter 8, Section 4
g of NaCl
29
Solution
How many grams of NaCl are needed to prepare 225 g
of a 10.0% (m/m) NaCl solution?
Step 3 Write equalities and conversion factors.
10.0 g of NaCl = 100 g of NaCl solution
Step 4 Set up the problem to calculate the mass or
volume.
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Chapter 8, Section 4
30
Learning Check
How many liters of a 2.00 M NaCl solution are needed to
provide 67.3 g of NaCl?
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Chapter 8, Section 4
31
Solution
How many liters of a 2.00 M NaCl solution are needed to
provide 67.3 g of NaCl?
Step 1 State the given and needed quantities.
Analyze the Problem.
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Given
Need
67.3 g NaCl
2.00 M NaCl solution
? liters NaCl
solution
Chapter 8, Section 4
32
Solution
How many liters of a 2.00 M NaCl solution are needed to
provide 67.3 g of NaCl?
Step 2 Write a plan to calculate the mass or volume.
g of NaCl
solution
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molar
mass
moles
NaCl
Chapter 8, Section 4
molarity
L of NaCl
33
Solution
How many liters of a 2.00 M NaCl solution are needed to
provide 67.3 g of NaCl?
Step 3 Write equalities and conversion factors.
1 mole of NaCl = 58.5 g of NaCl
2.00 mole of NaCl = 1 L of NaCl solution
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Chapter 8, Section 4
34
Solution
How many liters of a 2.00 M NaCl solution are needed to
provide 67.3 g of NaCl?
Step 4 Set up the problem to calculate the mass or
volume.
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Chapter 8, Section 4
35