Chemistry - A Molecular Science

Chapter 10 Solutions

THE OBJECTIVES OF CHAPTER 10 ARE TO: •

define and describe solutions;

-^

define various units of concentration;

-^

define solubility and describe the solution process;

-^

present simple principles for predicting solubilities;

-^

describe the function of detergents;

-^

define electrolytes and the natu

re of their aqueous solutions;

-^

introduce net equations; and

-^

describe solubility equilibria and define the solubility product constant.

10.1

CONCENTRATION The relative amounts of solute and solvent in

a solution are important characteristics of the

solution. They are usually given in terms of the

concentration

of the solute in the solvent

or solution. There are many concentration units, but we will consider only three.

%(m/m)

percent by mass

grams of solute/100 g of solution

%(V/V)

percent by volume

mL of solute/100 mL of solution

M

molarity

moles of

solute/L of solution

Percent by mass

is most commonly used in solid solutions. A 60/40 solder is a

solution of lead and tin that is 60% lead and 40% tin by mass.

Percent by volume

is used

for solutions of liquids in liquids. Ethylene glycol (C

H 2

O 6

) is a common antifreeze, which 2

gives a maximum freezing protection in a 50% mixture by volume. Thus, your car is best protected from freezing when half of the

volume

of the solution in the cooling system is

ethylene glycol and half is water. The grain alcohol or ethanol (C

H 2

OH) content in 5

alcoholic beverages is given in terms of

proof

, which is simply twice the percent by

volume of the alcohol in the solution. Thus, 100 mL of 90 proof rum contains 45 mL of C^2

H^5

OH. The mole is the most useful measure of amount in a chemistry laboratory because it is

easily related to the number of molecules or ions, so

molarity

is a very common unit of

concentration in the laboratory. A solution of sugar that is composed of 0.10 mole of sugar (C

H 12

O 22

) in a liter of solution is said to have a concentration of 0.10 M (read as 0.10 11

molar). The molarity of a solute is represented by enclosing its formula in square brackets; thus, the above sugar solution is one in which [C

H 12

O 22

] = 0.10 M. 11

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