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Measuring Concentration
Worksheet
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Parsons
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Printed: November 23, 2011
Author
Richard Parsons
Contributor
Dolly Kim
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Contents
1 The Solution Process
Worksheets
1.1
1
Measuring Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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Chapter 1
The Solution Process
Worksheets
1.1 Measuring Concentration
Concentration by Percent Mass Worksheet
CK-12 Foundation Chemistry
Name______________________ Date_________
The definition of percent mass concentration is the ratio of the mass of solute divided by the total mass of
the solution and multiplied by 100 to convert to a percentage.
percent by mass =
mass o f solute
× 100
mass o f solution
Example: What is the percent concentration by mass of a solution formed by dissolving 100. grams of
ethanol, C2 H5 OH, in 100. grams of water?
Solution: percent by mass =
mass o f solute
mass o f solution
× 100 =
100. g
200. g
× 100 = 50.0%
Example: If the density of a 10.0% by mass KNO3 solution in water is 1.19 g/mL, how many grams of
KNO3 are present in 100. mL of the solution?
Solution: We can multiply the volume times the density to the mass of the 100. mL of solution and then
take 10.0% of the mass of the solution to get the mass of the potassium nitrate.
grams o f solution = (100. mL)(1.19 g/mL) = 119 grams
grams o f KNO3 = (0.10)(119 grams) = 11.9 grams
Exercises
1. If 30.0 grams of AgNO3 are dissolved in 275 grams of water, what is the concentration of the silver
nitrate by mass percent?
2. How many grams of MgF2 are present in 100.0 g of a 20.0% MgF2 in water solution?
3. How many grams of water are present in the solution in question #2?
4. The density of a 30.0% by mass solution of NaOH in water is 1.33 g/mL. How many grams of NaOH
are required to prepare 500. mL of this solution?
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5. The density of pure water is 1.00 g/mL. What is the concentration gy percent mass of a solution
prepared by dissolving 85.0 grams of NaOH in 750. mL of water?
6. A solution is prepared by dissolving 66.0 grams of acetone, C3 H6 O, in 146.0 grams of water. The
density of the solution is 0.926 g/mL. What is the percent concentration of acetone by mass?
7. A 35.4% solution of H3 PO4 in water has a density of 1.20 g/mL. How many grams of phosphoric acid
are present in 300. mL of this solution?
Mole Fraction and Molality Worksheet
CK-12 Foundation Chemistry
Name______________________ Date_________
Mole Fraction
The definition of mole fraction is the ratio of the moles of solute divided by the total moles of the solution.
mole f raction =
moles o f solute
moles o f solution
Example: What is the mole fraction of ethanol in a solution prepared by dissolving 100. g of ethanol,
C2 H5 OH, in 100. g of water?
Solution:
100. g
= 2.17 moles
46.0 g/mol
100. g
moles water =
= 5.56 moles
18.0 g/mol
2.17 mols
= 0.281
mole f raction o f ethanol =
7.73 mols
moles ethanol =
Molality
The definition of molality is the ratio of the moles of solute divided by the kilograms of solvent.
molality =
moles o f solute
kilograms o f solvent
Example: What is the molality of a solution prepared by dissolving 100. g of ethanol, C2 H5 OH, in 100. g
of water?
100. g
= 2.17 moles
46.0 g/mol
2.17 mols
= 21.7 m
molality o f ethanol =
0.100 kg
moles ethanol =
Example: A 35.4% solution of H3 PO4 in water has a density of 1.20 g/mL. What is the mole fraction of
H3 PO4 in this solution and what is the molality?
Solution: We can choose a sample volume of this solution and get the mass of it by multiplying the
volume times the density. Suppose we choose a 1.00 L sample.
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mass of solution = (1000. mL)(1.20 g/mL) = 1200. grams
mass of H3 PO4 in the solution = (0.354)(1200. grams) = 425 grams
mass of H2 O = 1200. grams − 425 grams = 775 grams
425 g
moles H3 PO4 =
= 4.34 moles
98.0 g/mol
775 g
moles H2 O =
= 43.1 moles
18.0 g/mol
4.34 mol
mole fraction of H3 PO4 =
= 0.0916
47.4 mol
4.34 mol
molality =
= 5.60 m
0.775 kg
Exercises
1. What is the mole fraction of MgF2 in a solution that has 20.0 g of MgF2 dissolved in 80.0 grams of
water?
2. What is the molality of the solution in question 1?
3. The density of a 30.0% by mass solution of NaOH in water is 1.33 g/mL. What is the mole fraction
of NaOH in this solution?
4. What is the molality of the solution in problem 3?
5. What is the molality of a solution prepared by dissolving 4.00 g of NaCl in 100. g of water?
6. How many grams of beryllium chloride would you need to add to 125 g of water to make a 0.500 m
solution?
7. What would be the mole fraction of BeCl2 in the solution in problem 6?
8. A solution is prepared by dissolving 66.0 g of acetone, C3 H6 O, in 146.0 g of water. The density of
the solution is 0.926 g/mL. What is the molality of this solution?
9. What is the mole fraction of acetone in the solution in problem 8?
Molarity Worksheet
CK-12 Foundation Chemistry
Name______________________ Date_________
The definition of molarity is the ratio of the mols of solute divided by the volume of the solution.
molarity =
moles o f solute
liters o f solution
Example: What is the molarity of a solution prepared by dissolving 60.0 grams of NaOH in sufficient
water to produce 2.00 liters of solution?
Solution:
60.0 g
= 1.50 moles
40.0 g/mol
1.50 mol
molarity =
= 0.750 M
2.00 L
moles NaOH =
Example: What volume of 0.750 M NaOH solution will contain 10.0 gram of NaOH?
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10.0 g
= 0.250 moles
40.0 g/mol
mol
0.250 mol
volume =
=
= 0.333 L
M
0.750 mol/L
moles NaOH =
Exercises
1.
2.
3.
4.
5.
6.
7.
8.
What is the molarity of a solution in which 4.50 g of NaNO3 is dissolved in 265 mL of solution?
How many grams of ammonia, NH3 are present in 5.0 L of 0.100 M solution?
How many milliliters of 0.200 M NaOH solution is necessary to contain 6.00 grams of NaOH?
How many liters of 0.500 M CaF2 solution is required to contain 78.0 g of CaF2 ?
What mass of ammonium phosphate is needed to make 100. mL of 0.500 M (NH4 )3 PO4 solution?
What is the molarity of a solution prepared by dissolving 198 g of BaBr2 in 2.00 liters of solution?
How many grams of glycerine, C3 H8 O3 , are needed to make 100. mL of 2.60 M solution?
A test tube contains 10.0 mL of 3.00 M CaCO3 solution. How many grams of calcium carbonate are
in the tube?
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