Solutions
What is a solution?
• A solution is a mixture that has the same
composition, color, density, and even taste
throughout.
Solutes and Solvents
• To describe a solution, you may say that
one substance is dissolved in another.
• The substance being dissolved is the
solute, and the substance doing the
dissolving is the solvent.
• When a solid dissolves in a liquid, the
solid is the solute and the liquid is the
solvent.
Universal Solvent
• Water is often referred to as the universal
solvent because it can dissolve so many things.
• However, not all substances dissolve in water.
Some substances are non-polar and have no
separate positive and negative areas. Due to
this, they will not attract to polar molecules like
water.
• Ex: Oils, fats and lipids
Non-liquid Solutions
• Solutions can also be gaseous or even
solid.
• All mixtures of gases are solutions.
• Air is a solution of 78% nitrogen, 20%
oxygen, and small amounts of other
gases such as argon, carbon dioxide,
and hydrogen.
Dissolving Liquids and Gases
• When gases dissolve in gases or when
liquids dissolve in liquids, this movement
spreads solutes evenly throughout the
solvent, resulting in a homogeneous
solution.
Rate of Dissolving
• Sometimes the rate at which a solute
dissolves into a solvent is fast and other
times slow.
• There are several things
you can do to speed up
the rate of
dissolvingstirring,
reducing crystal size, and
increasing temperature
are three of the most
effective techniques.
Stirring
• Stirring a solution speeds up dissolving
because it brings more fresh solvent into
contact with more solute.
The fresh solvent attracts
the particles of solute,
causing the solid solute
to dissolve faster.
Crystal Size
• Another way to speed the dissolving of a
solid in a liquid is to grind large crystals
into smaller ones.
• Large crystals dissolve in water slowly
because the amount of surface area is
limited.
• Increasing the amount of surface area by
creating smaller particles increases the
rate of dissolving.
Temperature
• Increasing the temperature of a solvent
speeds up the movement of its particles.
• This increase
causes more
solvent particles to
bump into the
solute. As a result,
solute particles
break loose and
dissolve faster.
Controlling the Process
• Each technique, stirring, crushing, and
heating, is known to speed up the rate of
dissolving by itself. However, when two or
more techniques are combined, the rate of
dissolving is even faster.
How much can dissolve?
• If you continue adding sugar to lemonade,
eventually the point is reached when no
more sugar dissolves and the excess
granules sink to the bottom of the glass.
• Solubility is the
maximum amount of a
solute that can be
dissolved in a given
amount of solvent at a
given temperature.
Concentration
• A concentrated solution is one in which a
large amount of solute is dissolved in the
solvent.
• A dilute solution is one that has a small
amount of solute in the solvent.
Types of Solutions–Saturated
• A saturated solution is a solution that
contains all the solute it can hold at a
given temperature.
Saturated Solutions
• Generally, as the temperature
of a liquid solvent increases,
the amount of solid solute that
can dissolve in it also
increases. This table shows
the amounts of a few solutes
that can dissolve in 100 g of
water at different temperatures,
forming saturated solutions.
Solubility Curves
• Each line on the graph is called a solubility
curve for a particular substance.
• You can use a
solubility curve to
figure out how much
solute will dissolve at
any temperature given
on the graph.
1.
2.
3.
4.
5.
6.
How would you describe
NaClO3 with a
concentration of 80g/100g
of water at 40 °C?
____________________
With a concentration of
120g/100g water at 45
°C?
_____________________
With a concentration of
160g/100g water at 45
°C?
_____________________
Which salt is least affected
by temperature?
_____________________
Which is most affected by
temperature?
_____________________
How many grams of KBr
will form a saturated
solution in 100 g of water
at 50 °C?
_____________________
Unsaturated Solutions
• An unsaturated solution is any solution
that can dissolve more solute at a given
temperature.
• Each time a saturated solution is heated
to a higher temperature, it becomes
unsaturated.
Supersaturated Solutions
• A supersaturated solution is one that
contains more solute than a saturated
solution at the same temperature.
• Supersaturated
solutions are
unstable.
Solubility of Gases
• Shaking or pouring a solution of a gas in a
liquid causes gas to come out of the
solution.
• Agitating the solution exposes more gas
molecules to the surface, where they
escape from the liquid.
Pressure Effects
• Increasing the pressure of a gas forces the
gas to dissolve into a liquid.
• Soft drinks are bottled under increased
pressure.
• When the
pressure is
released, the
carbon dioxide
bubbles out.
Temperature Effects
• Another way to increase the amount of
gas that dissolves in a liquid is to cool the
liquid.
• This is just the opposite of what you do to
increase the speed at which most solids
dissolve in a liquid.
Sum it up!
• Solutes and Solvents make up a solution
• Solutions are homogeneous mixtures and can be made
of solids, liquids or gases.
• Water is aka the Universal Solvent
• There are 3 types of Solutions: Unsaturated, saturated
and supersaturated
• Solubility is the maximum amount of a solute that can
be dissolved in a given amount of solvent at a given
temperature.
• Solubility Curves show how solutes can dissolve at
different temperatures.
• We can increase the rate of solubility by increasing
temp, stirring, reducing solute size, and increasing
pressure .
Solubility Review Questions
1 In which of the following will sugar be
harder to dissolve?
a. Hot tea
b. Warm milk
c. Hot coffee
d. Iced tea
2 The substance that dissolves the solute is
called the
a. Solution
b. Solvent
c. Solid
d. Salt water
3 Which form of matter usually increases its
solubility as the temperature decreases?
a. Liquid
b. Gas
c. Solid
d. Ice
4 No matter how hot you make the tea, you
cannot dissolve any more sugar into the
solution. This is an example of a ____
solution.
a. Solvent
b. Hot
c. Heterogeneous
d. Saturated
5 Which of the following helps to increase
the rate of solubility in a liquid solution?
a. Stirring
b. Increasing temperature
c. Reducing crystal size of solute
d. All of the above
Answers
1.
2.
3.
4.
5.
D
B
B
D
D