WAYS OF EXPRESSING SOLUTION
CONCENTRATION
for General Chemistry 2/Grade 12-STEM
Quarter 3/Week 2.c-d
FOREWORD
This Self Learning Kit (SLK) focuses on the discussion of the
different
ways
of
expressing
solution
concentration
and
stoichiometric calculations involving solution. Sample calculations
and practice exercises are included to help you understand better
on the topic.
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OBJECTIVES:
At the end of the lesson, the learners are expected to:
K- Identify the different ways of expressing the concentration of
a solution.
S- Carry out stoichiometric calculations involving reactions in
solution.
A- Recognize the importance of understanding the different
ways of expressing solution concentration.
LEARNING COMPTENCIES:
- Use
different ways of expressing concentration of solutions:
percent by mass, mole fraction, molarity, molality, percent by
volume, ppm (STEM_GC11PPIIId-f-111).
- Perform stoichiometric calculations for reactions in solution
(STEM_GC11PPIIId-f-112).
I. WHAT HAPPENED
PRE-ACTIVITIES/PRE-TEST:
Directions: Choose the best answer. Write the letter of your
choice in your notebook.
1. It is a unit of concentration expressed as the number of moles of
solute dissolved in a liter (L) of solution.
A. molality
C. percent by mass
B. molarity
D. percent by volume
2. It is a general term expressing the amount of solute contained in
the given amount of material?
A. Concentration
C. Molality
B. Density
D. Molarity
3. It is a unit of concentration defined as the number of moles of
solute per kilogram of solvent.
A. molality
C. percent by mass
B. molarity
D. percent by volume
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4. If 10.0 g of NaCl is present in 200.0 mL of aqueous solution, what
is the concentration of the solution?
A. 0.02%
B. 0.05%
C. 5.0%
D. 20.0%
5. What are the parts of solution?
A. liquid and salt
B. solid and salt
C. solution and solute
D. solvent and solute
6. Which of the following is an example of a solute-solvent
combination when table salt is dissolve in water?
A. gas-gas
C. solid-liquid
B. liquid-gas
D. solid-solid
7. A solvent is _____.
A. always a liquid
B. always water
C. the substance being dissolved
D. the substance present in the greatest amount
8. A solution may contain ___________.
A. many solvents and many solutes
B. many solvents but only one solute
C. only one solvent but many solute
D. only one solvent and one solute
9. What is the concentration of solution in %(m/m) if 10.0 g solute
dissolved in 90.0 g solvent?
A. 0.1000%
C. 10.00%
B. 0.1111%
D. 11.11%
10. The concentration of 0.50 mole solute in 500.00 mL solution is _.
A. 0.001mol/L
C. 0.100 mol/L
B. 0.010 mol/L
D. 1.00 mol/L
II. WHAT I NEED TO KNOW
DISCUSSION:
Recall your previous lesson about solution. In Chemistry,
solution is a homogeneous mixture composed of solute, the
dissolved matter in a solution and solvent, a substance capable of
dissolving other substances. The quantity of solute present in a given
quantity of solvent or solution is called concentration.
Several methods can be used to quantitatively express the
concentration of the solution. These include percent by mass,
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percent by volume, percent mass by volume, mole fraction,
molarity, molality and parts per million (ppm).
Ways of Expresing Solution Concentration
1. Percent by Mass (m/m)
• It is referred as the mass of solute, in grams(g), present in
100 g of solution .
Example 1. A sample of 0.446 g sodium chloride (NaCl) is dissolved
in 27.3 g water (H2O). What is the percent by mass of NaCl?
Given: mass of NaCl (solute)= 0.446 g
mass of H2O (solvent)= 27.3 g
% NaCl =?
Solution:
2. Percent by Volume(v/v)
• It is referred as the volume of solute present in 100 mL of solution.
Example 2. A 1.75-L bottle wine contains 560 mL of ethanol. What
is the v/v percent concentration of ethanol?
Given: volume of ethanol (solute) = 560 mL
volume of wine (solution) = 1.75 L or 1750 mL
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% ethanol = ?
Solution:
3. Percent mass by volume(m/v)
• It is referred as the mass of solute, in g, present in 100 mL of
solution.
Example 3. If 30.0 g calcium chloride, CaCl 2, is present in 0.5000 L of
aqueous solution, what is its concentration in terms of
mass/volume percent?
Given: mass of CaCl2 = 30.0 g
volume of solution = 0.5000 L or 500.0 mL
%CaCl2 =?
Solution:
4. Parts Per Million, ppm
• This unit of concentration is referred as the parts of a
component per million parts (10 6 or 1,000,000) of the
solution and is usually used if the quantity of solute present
in a solution is very small.
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Example 4. If there is 1.102 mg of silver (Ag) in 696 g of
solution, what is the concentration of Ag in ppm?
Given: mass of Ag= 1.102 mg or 1.102x10-3 g
mass of solution=696 g
concentration of Ag in ppm=?
Solution:
5. Molarity
• Molarity is another unit of concentration defined as moles of
solute per liter of solution.
Example 5. What is the molarity of a solution containing 37.4 g
of NaCl in 6.8 liters solution?
Given: mass of NaCl = 37.4 g (must be converted to moles)
Volume of solution = 6.8 L
Molarity =?
Solution:
moles of solute
L of solution
1 mole NaCl
37.4 g NaCl
58.44 g NaCl
=
6.8 L
M=
M = 0.094 mol/L
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Na = 22.99 g/mol
Cl = 35.45 g/mol
58.44 g/mol
Moles = m/mm
6. Molality
• It is the number of moles of solute dissolved in 1 kilogram of
solvent.
Example 6.1 Calculate the molality of a sulfuric acid solution
containing 48.8 g of sulfuric acid in 396 g of water.
Given: mass of sulfuric acid, H2SO4=48.8 g
mass of water(solvent)=396 g
molality=?
Solution:
Example 6.2. Calculate the molality of a 10.0 % CaCl 2 by weight.
(Atomic mass: Ca=40.08 g/mol, Cl= 35.45 g/mol)
Given: 10.0% CaCl2(10.0 g CaCl2 /100.0 g solution)
Solution:
• Calculate mole CaCl2
• Calculate Molality
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Solution = Solute +Solvent
Solvent = Solution-Solute
Solvent = 100.0 g-30.0g
Solvent = 70.0g (or 0.0700 kg)
Mol/kg
7. Mole Fraction
• It is a unitless quantity that expresses the ratio of the number
of moles of one component to the total number of moles of
the solution.
Example 7. A solution is prepared by adding 400.8 g ethanol,
C2H5OH to 287.8 g H2O. Calculate the mole fractions of these two
components. (Molar masses: C2H5OH= 46.07 g/mol; H2O=18.02
g/mol)
Given: mass of C2H5OH = 400.8 g
Mass of H2O = 287.8 g
Xethanol =?
Xwater =?
Solution:
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Practice Exercise
Direction: Solve the following problems and show your solutions in
your notebook.
1. A 60-mL solution contains 8.6 g of ethanol and 0.042 g of
antiseptic. Calculate the concentration of each component in
mass/volume percent. (Ans. Ethanol = 14%; antiseptic = 0.70%)
2. What is the molarity of the solution made from 40.0 g NaOH in
500.0 mL of solution? (Atomic Mass: Na = 22.99 g/mol; O = 16.00
g/mol; H = 1.008 g/mol; Ans. M = 2.00 mol/L)
3. Calculate the molality of phosphoric acid, H3PO4, in a solution of
29.0 g H3PO4 in 250.0 g H2O. (Atomic mass: H = 1.008 g/mol; P = 30.97
g/mol; O = 16.00 g/mol; Ans. m = 1.18 mol solute/kg solvent)
4. Refer to the data given in problem # 3, calculate the mole
fraction of H3PO4 and H2O. (Ans. XH3PO4 = 0.979; XH2O = 0.0209)
5. An aqueous solution has 0.0400 g of NaCl (solute) in 2.00 kg H2O
(solvent). What is the concentration of the solution in parts per
million? Hint: Convert mass of H2O to g. (Ans. 20.0 ppm)
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Solution Stoichiometry
Understanding solution concentration is important because it
gives a concrete idea on how much solute and solvent are
necessary to prepare such solution. Also, in stoichiometric
calculation, solution concentration can be used as a conversion
factor to determine the amount of product that can be produced
in a chemical reaction.
Example 1. Determine the mass, in grams, of solid Mg(OH)2 that can
be produced if 90.0 mL of a 1.26 M Mg(NO3)2 solution completely
reacts with excess NaOH. (Atomic mass: Mg = 24.31 g/mol; O =
16.00 g/mol; N = 14.01 g/mol; Na = 22.99 g/mol; H = 1.008 g/mol)
Given: 90.0 mL of 1.26 M Mg(NO3)2
mass of Mg(OH)2 = ?
Solution:
• Before you will answer the problem, try to recall your previous
lesson on the following:
✓ Writing chemical formula, the crisscross method.
✓ Types of chemical reaction, such as, combination, single
replacement, double replacement.
• To calculate the amount of magnesium hydroxide, Mg(OH)2,
produced, first, we must write the balance chemical equation.
• Then, calculate moles of Mg(NO3)2.
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• Next, calculate the mass of Mg(OH)2.
Example 2. Calculate the mass, in grams, of 6.00% H2O2 solution is
needed to produce 132.6 g of O2 (g).
Given: 6.00% H2O2
132.6 g O2
Solution:
• Write the balanced chemical equation
• Calculate moles O2.
• Calculate mass of H2O2 solution.
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Practice Exercise
Directions: Solve the following problems and show your solutions in
your notebook.
1. Calculate the volume, in mL, of 1.72 M HCl solution that will
react with 2.67 mol of CaCO3? (Ans. 3.10x103 mL)
2. If 0.650% solution of Na2CO3 will be used to precipitate Ca+2 from
solution, determine the amount of solution, in grams, needed to
precipitate 5.00x102mL of 0.01120M Ca+2? (Atomic mass: Na=22.99
g/mol; C=12.01 g/mol; O=16.00 g/mol; Ca= 40.08 g/mol; Ans. 91.3
g)
II. WHAT I HAVE LEARNED
EVALUATION/POST TEST:
I. Directions: Choose the best answer. Write the letter of your
choice in your notebook. Show all your work if applicable!
1. It referred as a measure of the amount of solute dissolved in a
specified quantity of solvent.
A. concentration
C. molarity
B. molality
D. solution
2. What is the molarity of a solution that contains 10.0 moles of
solute in 2000.0 mL solution?
A. 5.00x10-3 mol/L
C. 5.00 mol/L
B. 0.200 mol/L
D. 2.00x102mol/L
3. To determine the number of solute present in a solution, which
of the following operation will be used
A. molality x moles of solution
B. molality x volume of solution, L
C. molarity x moles of solution
D. molarity x volume of solution, L
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4. The mass of sucrose(C12H22O11) needed to prepare 250.0 mL of a
0.250M solution is ________. (Atomic mass: C=12.01 g/mol; H=1.008
g/mol; O=16.00 g/mol).
A. 0.0625 g
B. 1.00 g
C. 21.4 g
D. 34.2g
5. What is the molality of 30.0% NaCl by weight? (Atomic mass:
Na=22.99 g/mol; Cl=35.45 g/mol)
A. 0.513 m
B. 5.13 m
C. 7.33 m
D. 73.3 m
II. Direction: Answer the following word problems in your notebook.
Show your work!
1. Calculate the volume of 0.400 M H3PO4 needed to react with
200.0 mL of 0.200 M NaOH.
2. If 10.0g of glucose (C6H12O6) is present in 2.0 L of aqueous
solution, what is the concentration in terms of the following:
A) ppm
B) mass/volume percent
Atomic mass: C=12.01 g/mol; H=1.008 g/mol; O=16.00g/mol
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C) molarity
References
Expressing solution concentration
https://www.askiitians.com/iit-jee-solutions-colligativeproperties/expressing-concentration-of-solutions/
(accessed January 17,2021)
Helmenstine, Anne Marie, Ph.D. "What Is a Mole Fraction?"
ThoughtCo. https://www.thoughtco.com/mole-fraction-definitionchemistry-glossary-606379 (accessed January 25, 2021).
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SYNOPSIS
Answer Key
Solution concentration is the
measure of the amount of solute dissolved in
a specified quantity of solvent. It can be
expressed in several ways, such as, percent
by mass and volume, parts per million,
molality, molarity, and mole fraction. Also, in
stoichiometric
calculations,
units
of
concentration can be used as the
conversion factor in determining the desired
quantity.
.
ABOUT THE AUTHOR
Agustina C. Omaguing is a graduate of Bachelor of Science
in Chemistry at Negros Oriental State University (NORSU).
Also, she earned Education units at Foundation University,
and completed her academic requirements in Master of
Arts in Science Teaching at NORSU. Currently, she is a
Senior High School Teacher at Valencia National High
School.
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