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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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