8.2 Solubility and Concentration
Fresh lemonade is a
solution of water, lemon
juice, and sugar.
There is a limit to the
amount of sugar that
can dissolve in a given
amount of water. Once
that limit is reached, you
cannot make the
solution taste any
sweeter.
8.2 Solubility and Concentration
Solubility
How are solutions with different amounts of
solute described?
Solutions are described as saturated,
unsaturated, or supersaturated, depending
on the amount of solute in solution.
8.2 Solubility and Concentration
Solubility
The maximum amount of a solute that
dissolves in a given amount of solvent at a
constant temperature is called solubility.
Solubilities are usually expressed in grams of
solute per 100 grams of solvent at a specified
temperature.
8.2 Solubility and Concentration
Solubility
At a given temperature, different substances
have different solubilities in water.
8.2 Solubility and Concentration
Solubility
At a given temperature, different substances
have different solubilities in water.
8.2 Solubility and Concentration
Solubility
At a given temperature, different substances
have different solubilities in water.
8.2 Solubility and Concentration
Solubility
Saturated Solutions
A saturated solution is one that contains as
much solute as the solvent can hold at a
given temperature.
At 20°C, 203.9 grams of table sugar will
dissolve in 100 grams of water. If you add
more sugar, it will not dissolve.
8.2 Solubility and Concentration
Solubility
Unsaturated Solutions
A solution that has less than the maximum
amount of solute that can be dissolved is
called an unsaturated solution.
As long as the amount of solute is less than
the solubility at that temperature, the solution
is unsaturated.
8.2 Solubility and Concentration
Solubility
Supersaturated Solutions
A supersaturated solution is one that
contains more solute than it can normally
hold at a given temperature.
A solvent can sometimes dissolve more
solute than you might expect, based on its
solubility.
If you heat a solution, more solute may
dissolve. Carefully cool the solution without
jarring it and the extra solute in solution
remains.
8.2 Solubility and Concentration
Solubility
Supersaturated solutions are very unstable. When a
single crystal of sodium acetate is added to a
supersaturated solution of sodium acetate in water,
the excess solute rapidly crystallizes.
8.2 Solubility and Concentration
Factors Affecting Solubility
What factors determine the solubility of a
solute?
Three factors that affect the solubility of a
solute are the polarity of the solvent,
temperature, and pressure.
8.2 Solubility and Concentration
Solubility
Polar and Nonpolar Solvents
Oil does not dissolve in water because oil
molecules are nonpolar and water molecules
are polar.
Solutions are more likely to form when the
solute and solvent are either both polar or
both nonpolar.
A soap molecule has a polar end, which
attracts water molecules, and a nonpolar
end, which attracts oil.
8.2 Solubility and Concentration
Solubility
Generally, a solute is more likely to dissolve
in a “like” solvent than an “unlike” solvent.
8.2 Solubility and Concentration
Solubility
Soaps and detergents are used to remove
grease and oil stains.
8.2 Solubility and Concentration
Solubility
Temperature
In general, the solubility of solids increases
as the solvent temperature increases.
In general, gases become less soluble as the
temperature of the solvent increases.
8.2 Solubility and Concentration
Solubility
Pressure
Increasing the pressure on a gas increases
its solubility in a liquid.
The pressure of CO2 in a sealed 12-ounce
can of soda at room temperature can be two
to three times atmospheric pressure.
8.2 Solubility and Concentration
Concentration of Solutions
What are three ways to measure the
concentration of a solution?
The concentration of a solution is the amount
of solute dissolved in a specified amount of
solution.
Concentration can be expressed as percent
by volume, percent by mass, and molarity.
8.2 Solubility and Concentration
Concentration of Solutions
Percent by Volume
Most bottled or canned juices are
made by adding water to natural
fruit juices. These solutions are
less concentrated than natural
fruit juices.
Percent by volume is a way to
measure the concentration of one
liquid dissolved in another.
8.2 Solubility and Concentration
Concentration of Solutions
Use the following equation to calculate
concentration as a percent by volume.
8.2 Solubility and Concentration
Concentration of Solutions
Percent by Mass
Concentration expressed as a percent by
mass is more useful when the solute is a
solid.
Percent by mass is the percent of a solution’s
total mass that is accounted for by a solute.
8.2 Solubility and Concentration
Concentration of Solutions
Molarity
To compare the number of solute particles in
solutions, chemists often use moles to
measure concentration.
Molarity is the number of moles of a solute
dissolved per liter of solution.
8.2 Solubility and Concentration
Concentration of Solutions
To make a 1-molar (1M) solution of sodium
chloride in water, first calculate the molar
mass of the solute. Sodium chloride, NaCl,
has a molar mass of 58.5 grams.
If 58.5 grams of sodium chloride is mixed with
enough water to make one liter of solution,
the resulting solution is 1-molar.
8.2 Solubility and Concentration
Concentration of Solutions
One liter of a 1M NaCl solution contains 58.5
grams of NaCl.
8.2 Solubility and Concentration
Assessment Questions
1. Compound X has a solubility of 20 g in 100 g of
water at 20°C. What is the minimum amount of
water needed to dissolve 50 g of compound X?
a.
b.
c.
d.
250 g
100 g
500 g
200 g
8.2 Solubility and Concentration
Assessment Questions
1. Compound X has a solubility of 20 g in 100 g of
water at 20°C. What is the minimum amount of
water needed to dissolve 50 g of compound X?
a.
b.
c.
d.
250 g
100 g
500 g
200 g
ANS: A
8.2 Solubility and Concentration
Assessment Questions
2. A saturated solution of carbon dioxide in water
suddenly experiences an increase in pressure.
What happens to the solution?
a. Bubbles form as the carbon dioxide comes out of the
water.
b. It becomes supersaturated.
c. It remains saturated.
d. More carbon dioxide can now be dissolved in the water.
8.2 Solubility and Concentration
Assessment Questions
2. A saturated solution of carbon dioxide in water
suddenly experiences an increase in pressure.
What happens to the solution?
a. Bubbles form as the carbon dioxide comes out of the
water.
b. It becomes supersaturated.
c. It remains saturated.
d. More carbon dioxide can now be dissolved in the water.
ANS: D
8.2 Solubility and Concentration
Assessment Questions
3. How does the number of particles in a 1 M solution of LiOH
(molar mass = 24) compare to the number of particles in a
1 M solution of NaCl (molar mass = 58.5)?
a.
b.
c.
d.
There are more particles of solute in the LiOH solution.
There are more particles of solute in the NaCl solution.
The number of particles of solute is the same in both solutions.
More information is necessary in order to compare the solutions.
8.2 Solubility and Concentration
Assessment Questions
3. How does the number of particles in a 1 M solution of LiOH
(molar mass = 24) compare to the number of particles in a
1 M solution of NaCl (molar mass = 58.5)?
a.
b.
c.
d.
There are more particles of solute in the LiOH solution.
There are more particles of solute in the NaCl solution.
The number of particles of solute is the same in both solutions.
More information is necessary in order to compare the solutions.
ANS:
B