CHAPTER 8
Solutions, Acids, and Bases
8.1 Formation of Solutions
Dissolving

Recall that a solution is a homogeneous mixture of
two or more substances
 Every
solution has two components:
 Solute

Substance whose particles are dissolved in a solution
 Solvent

 Ex.
Substance in which the solute dissolves
Seawater – water is solvent, salt is solute
Dissolving

Solutes and solvents can take the form of solid,
liquid, or gas
 Solution

takes state of solvent
Substances can dissolve in water in three ways
 Dissociation
 Dispersion
 Ionization
Dissociation of Ionic Compounds

For a solute to dissolve in water
 The
solute and solvent particles must attract to one
another
 The
solute particles are attracted and the solvent particles
are attracted to one another
 So,
before a solution can form, those attractions must be
overcome
 Process in which an ionic compound seperates into ions
as it dissolves is called dissociation
Dispersion of Molecular Compounds

The water in your saliva dissolves the sugar and
flavoring in candy throughout your mouth
 Sugar
dissolves in water by dispersion, or breaking
into small pieces that spread throughout the water
 Both
sugar and water are polar, therefore attract
 When enough water molcules have surrounded the sugar
molecule, sugar molecule breaks free and is pulled into
solution
Ionization of Molecular Compounds

HCl – molecular compound where hydrogen and
chloride share an electron
 When
HCl gas dissolves in water, the H molecule is
transferred to water
 H30+
and Cl- are produced
 When
a neutral molecule gain or lose electrons it is
known as ionization

This is a chemical change
 Unlike
dispersion and dissociation
Properties of Liquid Solutions

Three physical properties of a solution that can
differ from those of its solute and solvent are:
 Conductivity
 Freezing
point
 Boiling point
Conductivity

Solid sodium chloride is a poor conductor
 When
it dissociates in water, the sodium and chloride
ions are able to move freely
 They
will then conduct electricity
Freezing Point and Boiling Point

MgCl2 is what is sometimes spread on icy roads
 When
it dissolves in melting ice, it dissociates into
Mg2+ and Cl These ions are able to interfer with freezing process
 Salted
roads have a freezing point of -15°C
Freezing Point and Boiling Point

Solute can also raise boiling point
 ex.
Coolant used in most car radiators
 Adding ethylene glycol to water raises the boiling point
 Solution helps prevent the engine from overheating
 Also
prevents the the liquid from freezing in the winter
Heat of Solution

During the formation of a solution, energy is either
released or absorbed
 Can
be described as either exothermic or endothermic
 Dissolving
sodium hydroxide in water is exothermic, releases
heat
 How it Works box explains how cold packs are used
Heat of Solution

In order for a solution to form, all attractions must
be broken
 That
requires energy
 Formation of solutions, releases energy
 The
difference between these energies is called the heat of
solution
Factors Affecting Rates of Dissolving

Reates of dissolving depend on the frequency and
energy of collisions
 Formation
of solutions, collisions occur between solute
and solvent particles

Factors that affect the rate of dissoling include:
 Surface
area
 Stirring
 temperature
Factors Affecting Rates of Dissolving

The greater the surface area of a solid solute, the
more requent the collision are between the solute
and the solvent particles
 Increase

surface area by breaking into smaller pieces
Stirring
 Moves
dissolved particles away from surface
 Allows
more collisions between solute and solvent
Factors Affecting Rates of Dissolving

Increasing temperature is another way to speed up
dissolving
 Increase
in temperature causes the particles to move
faster
 Both the number of collisions and the energy of these
collisions increases
 Goes into solution more quickly
8.2 Solubility and Concentration
Solubility

Solubility
 The
max amount of a solute that dissolves in a given
amount of solvent at a constant temperature
 Usually

expressed in grams of solute in 100g of solvent
Solutions are described as:
 Saturated
 Unsaturated
 Supersaturated
Solubility

Saturated
 Sugar
is very soluble in water
 At 20 degrees C you can dissolve 203.9 grams of
sugar in 100g of water
 What

 The

will happen if you try to dissolve more than that?
The extra sugar will not go into solution
solution is already saturated
One that contains as much solute as the solvent can hold at a
given temperature
Solubility

Unsaturated
A
solution that has less than the max amount of solute
that can be dissolved
 many
beverages are unsaturated
Solubility

Supersaturated
 If
you heat a solvent above the average temperature it
can dissolve more solute
 If
you then carefully cool the solvent back to the average
without jarring it, you may be able to keep the extra solute
in the solution
 Supersaturated
 One
solution
that contains more solute than it can normally hold at a
given temperature
 Very unstable
 If a tiny particle falls into a supersaturated solution, the
extra solute may rapidly fall out
Factors Affecting Solubility

Have you ever tried to wash oil or grease off your
hands?
 Will
not come off in just water, but in soapy water it will
wash off
 Not

soluble in water, but in soapy water it is
Three factors that affect solubility:
 Polarity
of the solvent
 Temperature
 pressure
Factors Affecting Solubility

Polar and Nonpolar Solvents
 Oil
molecules are nonpolar, water is polar
 Common
guideline for predicting solubility is ‘like dissolves
like’
 More
likely to dissolve if solute and solvent are both
polar or both nonpolar
 Soap
molecules have a polar and non polar end
 Makes it easy to dissolve oil
Factors Affecting Solubility

Temperature
 In
general the solubility of a solute increases when you
increase the temperature of the solvent
 When water temp increases, bubbles start to come out
of the water
 These
are gas bubbles that are dissolved in water
 Unlike most solids, gases usually become less soluble as the
temperature of solvent increases
Factors Affecting Solubility

Pressure
 Incresing
the pressure on a gas increases its solubility in
a liquid
 Pressure of carbon dioxide in a 12 oz can of soda at
room temp can by two to three times atmospheric
pressure