Transcript 7.4 Percent Concentration

Chapter 7
Solutions
7.4
Percent Concentration
Copyright © 2009 by Pearson Education, Inc.
1
Percent Concentration
The concentration of a solution
is the amount of solute dissolved in a specific amount
of solution.
amount of solute
amount of solution
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Mass Percent
Mass percent (% m/m) is the
• concentration by mass of solute in a solution.
mass percent =
g of solute
x 100
g of solute + g of solvent
• amount in g of solute in 100 g of solution.
mass percent =
g of solute
a
100 g of solution
3
Mass of Solution
Add water to
give 50.00 g
of solution
8.00 g KCl
50.00 g of
KCl solution
Copyright © 2009 by Pearson Education, Inc.
4
Calculating Mass Percent
The calculation of mass percent (% m/m) requires the
• grams of solute (g KCl) and
• grams of solution (g KCl solution).
g of KCl
=
8.00 g
g of solvent (water)
=
42.00 g
g of KCl solution
=
50.00 g
8.00 g KCl (solute)
50.00 g KCl solution
x 100 = 16.0% (m/m)
5
Guide to Calculating Solution
Concentrations
Copyright © 2009 by Pearson Education, Inc.
6
Learning Check
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.
1) 15.0% (m/m) Na2CO3
2) 6.38% (m/m) Na2CO3
3) 6.00% (m/m) Na2CO3
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Solution
3) 6.00% (m/m) Na2CO3
STEP 1: mass solute = 15.0 g of Na2CO3
mass solution = 15.0 g + 235 g = 250. g
STEP 2: Use g solute/g solution ratio
STEP 3: mass %(m/m) = g solute x 100
g solution
STEP 4: Set up problem
mass %(m/m) = 15.0 g Na2CO3 x 100 = 6.00% Na2CO3
250. g solution
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Volume Percent
The volume percent (% v/v) is
• percent volume (mL) of solute (liquid) to volume (mL) of
solution.
volume % (v/v) = mL of solute x 100
mL of solution
• solute (mL) in 100 mL of solution.
volume % (v/v) = mL of solute
100 mL of solution
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Mass/Volume Percent
The mass/volume percent (% m/v) is
• percent mass (g) of solute to volume (mL) of solution.
mass/volume % (m/v) = g of solute x 100
mL of solution
• solute (g) in 100 mL of solution.
mass/volume % (m/v) =
g of solute
100 mL of solution
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Percent Conversion Factors
Two conversion factors can be written for each type
of % value.
Copyright © 2009 by Pearson Education, Inc.
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Learning Check
Write two conversion factors for each solutions.
A. 8.50% (m/m) NaOH
B. 5.75% (v/v) ethanol
C. 4.8% (m/v) HCl
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Solution
A. 8.50 g NaOH
100 g solution
and
100 g solution
8.50 g NaOH
B. 5.75 mL alcohol and
100 mL solution
100 mL solution
5.75 mL alcohol
C. 4.8 g HCl
and
100 mL solution
100 mL HCl
4.8 g HCl
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Using Percent Concentration (m/m)
as Conversion Factors
How many grams of NaCl are needed to prepare
225 g of a 10.0% (m/m) NaCl solution?
STEP 1: Given: 225 g solution; 10.0% (m/m) NaCl
Need: g of NaCl
STEP 2: g solution
g NaCl
STEP 3: Write the 10.0% (m/m) as conversion factors.
10.0 g NaCl
and
100 g solution
100 g solution
10.0 g NaCl
STEP 4: Set up using the factor that cancels g solution.
225 g solution x 10.0 g NaCl
= 22.5 g NaCl
100 g solution
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Learning Check
How many grams of NaOH are needed to prepare
75.0 g of 14.0% (m/m) NaOH solution?
1) 10.5 g of NaOH
2) 75.0 g of NaOH
3) 536 g of NaOH
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Solution
1) 10.5 g NaOH
75.0 g solution x 14.0 g NaOH = 10.5 g NaOH
100 g solution
14.0% (m/m) factor
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Learning Check
How many milliliters of a 5.75% (v/v) ethanol
solution can be prepared from 2.25 mL of ethanol?
1) 2.56 mL
2) 12.9 mL
3) 39.1 mL
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Solution
3) 39.1 mL
2.25 mL ethanol x 100 mL solution
5.75 mL ethanol
5.75% (v/v) inverted
= 39.1 mL of solution
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Using Percent Concentration (m/v)
as Conversion Factors
How many mL of a 4.20% (m/v) will contain 3.15 g of KCl?
STEP 1: Given: 3.15 g of KCl(solute); 4.20% (m/v) KCl
Need: mL of KCl solution
STEP 2: Plan: g of KCl
mL of KCl solution
STEP 3: Write conversion factors.
4.20 g KCl
and
100 mL solution
100 mL solution
4.20 g KCl
STEP 4: Set up the problem
3.15 g KCl x 100 mL KCl solution = 75.0 mL of KCl
4.20 g KCl
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Learning Check
How many grams of NaOH are needed to prepare
125 mL of a 8.80% (m/v) NaOH solution?
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Solution
How many grams of NaOH are needed to prepare
125 mL of a 8.80% (m/v) NaOH solution?
125 mL solution x 8.80 g NaOH =
100 mL solution
11.0 g of NaOH
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