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Ways of Expressing Concentration
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Ways of Expressing Concentration
MOLARITY (M)
mol of solute (n)
L of solutionM=
Because volume is temperature dependent, molarity
can change with temperature.
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Ways of Expressing Concentration
MOLARITY (M)
Example:
Calculate the molarity of each of the following
solutions:
a. 29.0 g of ethanol (C2H5OH) in 545 mL of solution,
b. 15.4 g of sucrose (C12H22O11) in 74.0 mL of
solution,
c. 9.00 g of sodium chloride (NaCl) in 86.4 mL of
solution.
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Ways of Expressing Concentration
MOLARITY (M)
Example:
Determine how many grams of each of the
following solutes would be needed to make 2.50
102 mL of a 0.100 M solution:
a. sulfuric acid (H2SO4)
b. sodium carbonate (Na2CO3),c. potassium dichromate (K2Cr2O7)
d. potassium permanganate (KMnO4).
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Ways of Expressing Concentration
MOLARITY (M)
Example:
Calculate the volume in mL of a solution required
to provide the following:a. 2.14 g of sodium chloride from a 0.270 M
solution
b. 4.30 g of ethanol from a 1.50 M solution
c. 0.85 g of acetic acid (CH3COOH) from a 0.30
M solution.
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MOLALITY (m)
mol of solute (n)
kg of solventM=
Ways of Expressing Concentration
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NORMALITY (N)
Number of equivalent weightsL of solutionN =
Ways of Expressing Concentration
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Example:
Normality
1) Calculate the (a) molarity and (b) Normality of a
solution prepared by dissolving 0.240 g of solid Ce(NO3)4
solute in enough water to make 250.0 mL of salt solution.
2) Calculate the mass of KMnO4which must be used to
prepare 200 mL of a solution whose concentration is:
a) 0.20N as a salt
b) 0.20N as an oxidizing agent in acidic mediumc) 0.20N as an oxidizing agent in neutral of basic
medium
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Mole fraction and Mole percent
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Mole fraction and Mole percent
Example:
1) What are the mole fractions of ethanol, C2H5OH, and
water in a solution prepared by mixing 70.0 g of ethanol with
30.0 g of water?
2) What are the mole fractions of ethanol, C2H5OH, and
water in a solution prepared by mixing 70.0 mL of ethanol
with 30.0 mL of water at 25C? The density of ethanol
is 0.789 g/mL, and that of water is 1.00 g/mL.
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1) Calculate the percent by mass of the solute in each
of the following aqueous solutions: (a) 5.50 g of NaBr in
78.2 g of solution, (b) 31.0 g of KCl in 152 g of water, (c)
4.5 g of toluene in 29 g of benzene.
Percentage Strength
2) Calculate the amount of water (in grams) that must
be added to (a) 5.00 g of urea (NH2)2CO in the
preparation of a 16.2 percent by mass solution, and
(b) 26.2 g of MgCl2in the preparation of a 1.5 percentby mass solution.
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Other Concentration Terms
ppm =mass of solute (g)
mass of solution (g)X 106
ppb = mass of solute (g)mass of solution (g)
X 109
p[solute] = -log [solute]
Proof strength = %(v/v) x 2
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Relationships between
concentration units
1) Sodium fluoride has a solubility of 4.22 g in 100.0 g of
water at 18C. Express the solute concentration in
terms of (a) mass percent, (b) mole fraction, and (c)
molality.
2) The density of an aqueous solution containing 12.50 g
K2SO4in 100.00 g solution is 1.083 g/mL. Calculate the
concentration of this solution in terms of molarity, molality,
percent of K2SO4, and mole fraction of solvent.
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