Transcript CH_7_4_Concentration_of_a_Solution

Chapter 7 Solutions
1
7.4
Concentration of a Solution
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution Concentration
2
The concentration of a solution is expressed as
amount of solute x
amount of solution
Units of concentration include:
• Mass percent (m/m)
• Volume percent (v/v)
• Mass/volume percent (m/v)
• Molarity (moles solute/liters solution)
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Mass Percent
3
Mass percent (% m/m) is the
• concentration by mass of solute in a solution
mass percent =
g of solute
 100
g of solute + g of solvent
• amount in g of solute in 100 g of solution
(conversion factor for mass percent)
mass percent =
g of solute x
100 g of solution
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Mass of Solute: Mass Solution
4
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Calculating Mass Percent
5
The calculation of mass percent (% m/m) requires the
• grams of solute (g KCl) and
• grams of solution (g KCl + g water) or
g of KCl
g of solvent (water)
g of KCl solution
+
=
8.00 g
42.00 g
50.00 g
8.00 g KCl (solute)  100 = 16.0% (m/m)
50.00 g KCl solution
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Guide to Calculating Solution
Concentration
6
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Learning Check
7
A solution is prepared by mixing 15.0 g of Na2CO3 and
235 g of H2O. Calculate the mass percent (% m/m) of
the solution.
A. 15.0% (m/m) Na2CO3
B. 6.38% (m/m) Na2CO3
C. 6.00% (m/m) Na2CO3
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
8
A solution is prepared by mixing 15.0 g of Na2CO3 and 235 g
of H2O. Calculate the mass percent (% m/m) of the solution.
Step 1 Determine the quantities of solute and solution.
mass solute = 15.0 g Na2CO3
mass solution = 15.0 g Na2CO3 + 235 g H2O = 250. g
Step 2 Write the concentration expression.
Use g solute/g solution ratio:
mass % (m/m) = g solute  100
g solution
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
9
A solution is prepared by mixing 15.0 g of Na2CO3 and 235 g
of H2O. Calculate the mass percent (% m/m) of the solution.
Step 3 Substitute solute and solution quantities into the
expression.
mass % (m/m) = 15.0 g Na2CO3  100 = 6.00% Na2CO3
250. g solution
The answer is C, 6.00% Na2CO3.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Volume Percent
10
The volume percent (% v/v) is
• percent volume (mL) of solute (liquid) to volume (mL)
of solution
volume % (v/v) =
mL of solute  100
mL of solution
• solute (mL) in 100 mL of solution
(conversion factor for volume percent)
volume % (v/v) =
mL of solute
100 mL of solution
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Mass/Volume Percent
11
The mass/volume percent (% m/v) is
• percent mass (g) of solute to volume (mL) of solution
mass/volume % (m/v) =
g of solute  100
mL of solution
• solute (g) in 100 mL of solution
(conversion factor for mass/volume percent)
mass/volume % (m/v) =
g of solute
100 mL of solution
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Learning Check
12
Write two conversion factors for each solution.
A. 8.50% (m/m) NaOH
B. 5.75% (v/v) ethanol
C. 4.8% (m/v) HCl
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
13
A. 8.50 g NaOH
100 g solution
and
B. 5.75 mL alcohol and
100 mL solution
C.
4.8 g HCl
and
100 mL solution
100 g solution
8.50 g NaOH
100 mL solution
5.75 mL alcohol
100 mL HCl
4.8 g HCl
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Molarity
14
Molarity (moles of solute/liter of solution) is moles of solute
per volume (L) of solution.
M =
moles solute = 1.0 mole NaCl
liter of solution
1 L solution
= 1.0 M NaCl solution
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Preparing a 1.0 M Solution
15
A 1.0 M NaCl solution
is prepared
• by weighing out 58.5 g
of NaCl (1.0 mole) and
• adding water to make
1.00 liter of solution
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Molarity Calculations
16
What is the molarity of 0.500 L of NaOH solution if it
contains 6.00 g of NaOH?
Step 1 Determine the quantities of solute and solution.
Solute: 1 mole of NaOH = 40.0 grams of NaOH
1 mole NaOH
and
40.0 g NaOH x
40.0 g NaOH
1 mole NaOH
6.00 g NaOH  1 mole NaOH = 0.150 mole of NaOH
40.0 g NaOH
The volume of the solution is 0.500 L.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Molarity Calculations
17
What is the molarity of 0.500 L of NaOH solution if it
contains 6.00 g of NaOH?
Step 2 Write the concentration expression.
M = moles solute
L solution
Step 3 Substitute solute and solution quantities into the
expression.
M = moles solute = 0.150 mole NaOH = 0.300 M NaOH
L solution
0.500 L solution
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Learning Check
18
What is the molarity of 0.225 L of a KNO3 solution
containing 34.8 g of KNO3?
A. 0.344 M
B. 1.53 M
C. 15.5 M
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
19
What is the molarity of 0.225 L of a KNO3 solution
containing 34.8 g of KNO3?
Step 1 Determine the quantities of solute and solution.
Solute: 1 mole of KNO3 = 101.1 grams of KNO3
1 mole KNO3
and
101.1 g KNO3
101.1 g KNO3
1 mole KNO3
34.8 g KNO3  1 mole KNO3 = 0.344 mole of KNO3
101.1 g KNO3
The volume of the solution is 0.225 L.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
20
Step 2 Write the concentration expression.
M=
moles solute
L solution
Step 3 Substitute solute and solution quantities into the
expression.
M = moles solute = 0.344 mole of KNO3 = 1.53 M KNO3
L solution
0.225 L solution
The answer is B, 1.53 M KNO3.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Molarity as a Conversion Factor
21
The units of molarity are used as conversion factors in
calculations with solutions.
Molarity
Equality
3.5 M HCl
1 L = 3.5 moles of HCl
Written as Conversion Factors
3.5 moles HCl
and
1L
1L
3.5 moles HCl
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Conversion Factors from
Concentrations
22
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Learning Check
23
How many grams of NaOH are needed to prepare 75.0 g
of 14.0% (m/m) NaOH solution?
A. 10.5 g of NaOH
B. 75.0 g of NaOH
C. 536 g of NaOH
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
24
How many grams of NaOH are needed to prepare 75.0 g of
14.0% (m/m) NaOH solution?
Using the conversion factor for mass percent:
75.0 g solution  14.0 g NaOH = 10.5 g of NaOH
100 g solution
14.0% (m/m) factor
The answer is A, 10.5 g of NaOH.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Learning Check
25
How many milliliters of a 5.75% (v/v) ethanol solution can
be prepared from 2.25 mL of ethanol?
A. 2.56 mL
B. 12.9 mL
C. 39.1 mL
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
26
How many milliliters of a 5.75% (v/v) ethanol solution can
be prepared from 2.25 mL of ethanol?
Using the conversion factor for volume percent:
2.25 mL ethanol  100 mL solution = 39.1 mL of solution
5.75 mL ethanol
5.75% (v/v) inverted
The answer is C, 39.1 mL of solution.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Learning Check
27
How many grams of AlCl3 are needed to prepare 125 mL of
a 0.150 M solution?
A. 20.0 g of AlCl3
B. 16.7 g of AlCl3
C. 2.50 g of AlCl3
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.
Solution
28
How many grams of AlCl3 are needed to prepare 125 mL of a
0.150 M solution?
0.125 L  0.150 mole AlCl3  133.5 g AlCl3 = 2.50 g of AlCl3
1L
1 mole AlCl3
molarity
conversion factor
molar mass
The answer is C, 2.50 g of AlCl3.
Chemistry: An Introduction to General, Organic, and Biological Chemistry, Eleventh Edition
Copyright © 2012 by Pearson Education, Inc.