Chapter 8
Section 8.1
FORMATION OF SOLUTIONS
Formation of Solutions
 A solution is a homogeneous mixture of two or
more substances, consisting of ions or
molecules.
 For a solution to form, one substance must
dissolve in another.
Solute and Solvent
 Too simplify:
 What two things make up a solution?
 A solute and a solvent.
 What is a solute?
 Something that gets dissolved in a solvent.
 What is a solvent?
 Something that dissolves a solute.
Types of Solutions
 Solutions may exist as gases, liquids, or
solids.
 The solute is the dissolved substance. In
the case of a solution of a gas or solid in a
liquid, it is the gas or solid. Otherwise, it is
the component of lesser amount.
 The solvent is the dissolving medium.
Generally it is the component of greater
amount.
Examples of Solutions
Type
Gas in Gas
Gas in liquid
Example
Solute
Solvent
Air
Oxygen
Nitrogen
Soda
Carbon dioxide
(gas)
Water
(liquid)
Solid in Liquid
Seawater
Salt (solid)
Water (Liquid)
Liquid in Liquid
Windshield
Washer
Alcohol
Water
Solid in Solid
Brass
Zinc (solid)
Copper (solid)
Substances Dissolving in Water
Three Ways:
 Dissociation
 Dispersion
 Ionization
Dissociation
 Ionic compounds
 metal + nonmetal (Binary and Multivalent)
 metal + polyatomic anion
 polyatomic cation + anion
 When ionic compounds dissolve in water the
anions and cations are separated from each
other; this is called dissociation
 We know that ionic compounds dissociate
when they dissolve in water because the
solution conducts electricity
Dispersion of Molecular Compounds
 Sugar dissolves in water by dispersion, or
breaking into small pieces that spread
throughout the water.
 A substance dissolves in water by breaking up
into smaller pieces. These pieces of the same
substance spread throughout the water. This
process is known as dispersion.
Ionization of Molecular Compounds
 The process in which neutral molecules gain
or lose electrons is known as ionization.
 Unlike dissociation and dispersion, which are
physical changes, dissolving by ionization is a
chemical change. The solution that results
contains new substances.
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
 The current is carried by dissolved ions
 The ability of an ion to carry current is a
function of:
 Ions charge (more charge, more current)
 Ions mass or size (larger ions, conduct less)
Freezing Point
 Freezing Point Depression
 Lowering the freezing point of a solution
as a result of the dissolved solute
 The presence of solute particles affects
how the solvent freezes.
Boiling Point
 Boiling Point Elevation
 Raising the boiling point of a substance by
adding solute
Heat of Solution
 During the formation of a solution, energy is either released or




absorbed.
Like chemical reaction, the solution process can be described as
exothermic or endothermic.
Dissolving sodium hydroxide in water is exothermic because it
releases heat. Dissolving ammonium nitrate is endothermic
because it absorbs heat.
In order for a solution to form, both the attractions among
solute particles and the attractions among solvent particles
must be broken.
In an exothermic reaction, the amount of energy required to
break the attractions among the solute particles and among
the solvent particles is less than the energy released as
attractions form between solute and solvent particles.
Heat of Solution
 In an exothermic reaction, the amount of energy
required to break the attractions among the
solute particles and among the solvent particles
is less than the energy released as attractions
form between solute and solvent particles.
 The formation of attractions releases energy.
 The difference between these energies is
known as the heat of solution.
Factors Affecting Rates of Dissolving
 Like rates of chemical reactions, rates of
dissolving depend on the frequency and energy
of collisions that occur between very small
particles.
 During a chemical reaction, collisions occur
between particles of the reactants.
 During the formation of a solution, collisions
occur between particles of the solute and
solvent.
 Factors that affect the rate of dissolving include
surface area, stirring, and temperature.
Factors Affecting Rates of Dissolving
 Temperature
 If we heat particles they will move faster
 The solvent will carry the solute particles away
faster
 So… Hotter Faster
Factors Affecting Rates of Dissolving
 Stirring or Shaking
 Stirring or shaking a solution moves the solute
particles around so that they are closer to
water particles
 the water particles can then attract them
easily and carry them away!
 So…. Dissolve Faster
Factors Affecting Rates of Dissolving
 Surface Area
 When broken into small particles
 the water particles can then attract them
easily and carry them away!
 When solute is broken up, there is more
surface area where dissolving can occur
 So…smaller surface area faster dissolves