Chem 116 Lecture Note Outlines
Set 02: Concentration Units
Four common concentration units
1. Molarity
2. Weight Percent (Wt %), ppm, ppb
3. Molality
4. Mole Fraction
♦
−
Molarity, M
♦ tells you how many moles of solute are present in every liter of solution (solute-to-solution)
Molarity, M =
moles of solute
liters of solution
♦
Weight Percent (Wt %), parts per million (ppm) and parts per billion (ppb)
The weight-weight percent, tells you how many grams of solute are present per hundred grams of
the solution
%(w/w ) =
mass solute
× 100%
mass solution
The weight-volume percent tells you how many grams of solute are present per 100 mL of
solution.
%(w/v ) =
mass solute
× 100%
volume solution
Related concentration Units:
 mass solute 
6
parts per million, ppm = 
 (1 × 10 ppm)
mass
solution


 mass solute 
9
parts per billion, ppb = 
 (1 × 10 ppb)
mass
solution


♦
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Page 1 of 6
Chem 116 Lecture Note Outlines
Set 02: Concentration Units
Molality
♦ tells you how many moles of solute are present in every kilogram of solvent
molality, m =
moles solute
kg solvent
♦
Mole Fraction
♦
Concentration Units/ Summary
Molarity, M
moles solute
M=
L soln
Mole fraction, Xi
moles of i
Xi =
total moles
Mass percent, %
(m/m)
mass i
%=
× 100%
mass soln
Molality, m
moles solute
m=
kg solvent
Spring 2016 (Ratcliff)
units
moles
L
Advantages
Useful in stoichiometry;
M×V= mole if V is in liters
Disadvantages
Temperature dependent
Must know density to find
solvent mass
None,
unitless
Temperature independent;
useful in special applications
Must know density to convert to
molarity
%
Temperature independent;
useful for small amounts
Must know density to convert to
molarity
moles
kg
Temperature independent;
used in special applications
Must know density to convert to
molarity
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Page 2 of 6
Chem 116 Lecture Note Outlines
Set 02: Concentration Units
Concept Check
Which contains more solute particles: a 0.10 M aqueous solution of methanol (CH3OH) or a 0.10 M
aqueous solution of salt (NaCl)?
a. Neither solution contains solute particles.
b. They contain the same number of solute particles
c. The salt solution contains twice as many particles as the methanol solution.
d. The methanol solution contains three times as many particles as the salt solution.
116_PSV_02_conc_01
Determine the concentration of H2SO4 in a solution prepared by dissolving 25.0 g of H2SO4 in 1.30 kg
of water in the following units?
wt % (w/w) of H2SO4
Wt %(H2SO4) = 1.89 %
mole fraction of H2SO4
XH2SO4 = 0.00352
Molality of H2SO4
m = 0.195
mole
kg
116_PSV_02_conc_02
A solution is 7.5 m MgCl2. What is the mole fraction of MgCl2 in the solution?
XMgCl2 = 0.12
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Page 3 of 6
Chem 116 Lecture Note Outlines
Set 02: Concentration Units
116_PSV_02_conc_03
A 0.944 M solution of glucose, C6H12O6 in water has a density of 1.0624 g/ml at 20 ºC. What is the
concentration of this solution in the following units?
Mole fraction of glucose
X= 0.0187
Mass percent (w/w) of glucose
16.0 %
Molality of glucose
1.06
mole
kg
116_PSV_02_conc_04
The density of a 16.0 % (w/w) solution of sulfuric acid (H2SO4) in water is 1.1094 g/ml at 25.0 ºC.
What is the concentration of this solution in the following concentration units?
molarity of H2SO4
1.81
Spring 2016 (Ratcliff)
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mole
L
Page 4 of 6
Chem 116 Lecture Note Outlines
Set 02: Concentration Units
Molality of H2SO4
1.94
mole
kg
mole fraction of H2SO4
0.0338
Concept Check
Which of the following does not exist in aqueous solution?
a. Ca2+(aq)
b. CH3COOH(aq)
c. CH3COO–(aq)
d. NaCl(aq)
116_PSV_02_conc_05
The EPA maximum standard for lead (Pb2+) is in drinking water is 15 ppb. If a 5.0 L sample of your
tap water contains 0.30 mg Pb2+(aq), will the EPA deem your water safe to drink?
Will the EPA deem your water safe to drink?
No. [Pb2+]= 60. ppb
What is the concentration of Pb2+ in your tap expressed in molarity
[Pb2+]= 2.9×10−7 mole
L
Spring 2016 (Ratcliff)
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Page 5 of 6
Chem 116 Lecture Note Outlines
Set 02: Concentration Units
Extra Practice Problems
116_PSV_02_conc_06
What is the Weight% (w/w) concentration of each of the following solutions?
Dissolve 0.655 moles of citric acid, C6H8O7, in 1.00 kg water.
11.2 %
116_PSV_02_conc_07
Procaine hydrochloride (MM = 272.77 g/mol) is used as a local anesthetic. Calculate the molarity of a
4.666 m solution which has a density of 1.1066 g/mL
2.272
mole
L
116_PSV_02_conc_08
An aqueous solution of glycerol, C3H8O3 (MM = 92.09), is 48.0% glycerol by mass and has a density
of 1.120 g mL-1. Calculate the molarity of the glycerol solution
5.84
mole
L
116_PSV_02_conc_09
Sodium hydroxide is a common ingredient in drain cleaners such as Drano. The mole fraction of
sodium hydroxide in a saturated aqueous solution is 0.310. What is the molality of NaOH in the
solution? (MM of H2O is= 18.02 /mole)
24.9
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mole
kg
Page 6 of 6