Chapter 12 Notes
In chapter 3, we learned about mixtures and that they exist in 2 forms: homogeneous (consistent
composition) and heterogeneous (inconsistent composition). Within these 2 types, mixtures will fall
into three classifications. They are solutions, suspensions, and colloids.
SOLUTIONS
When you place salt or sugar into water, you say it dissolves. The proper term is SOLUBLE or capable of
dissolving. Molecules of two compounds mix together to form a mixture of uniform distribution make a
SOLUTION.
Characteristics of a solution
o
o
o
o
o
Homogeneous
Particle size is 0.01 nanometer - 1 nanometer (atoms, ions,
molecules)
Do not separate or settle out
Does not filter
Do not scatter light
A solution consists of two parts. The component dissolved is the SOLUTE and the
medium in which the solute is dissolved is the SOLVENT.
The solute of a solution can be classified as an ELECTROLYTE or NON-ELECTROLYTE. Ionic compounds
(bonded together by the electrical attraction of cations and anions) will ionize into their ionic parts.
Both cations and anions will exist in the solution. These compounds produce a solution when dissolved
in water that will conduct electricity. If an electric current is not conducted, then the solution is
considered to be a non-electrolyte.
SUSPENSIONS
If the particles of the solute are large enough to settle out unless the mixture is
constantly stirred, the mixture is considered to be a SUSPENSION.
Characteristics of a suspension
o
o
o
o
o
Heterogeneous
Particle size is greater than 1000 nanometers
Will settle out
Can be filtered
May scatter light, generally are not transparent.
COLLOIDS
If the particle size falls between that of a solution and a
suspension, the mixture is said to be a COLLOID. The
particles are small enough that the kinetic molecular
energy of the solvent keeps the particles dispersed.
Characteristics of a colloid
o
o
o
o
o
Heterogeneous
Particle size is between 1 nanometer and
1000 nanometers
Particles will not settle out
Cannot be filtered
Will scatter light, the ability to scatter light is known as the TYNDALL EFFECT
There are 3 factors that contribute to the rate a solute will dissolve into a solvent.
1. Surface Area – The greater the surface area, the faster a solute will dissolve. Dissolving occurs at
the surface of the solute, so more surface area provides more opportunity for dissolution to
take place.
2. Agitation – The greater the agitation (stirring), the faster a solute will dissolve. The
concentration of the dissolved solute is the greatest near the surface of the solute. Stirring
allows for the solvent containing dissolved solute to be moved out of the way and replaced with
fresh solvent.
3. Temperature – The greater the temperature, the faster a solute will dissolve. The kinetic
molecular theory, explains that at higher temperature the motion of particles is faster. The
increased particle speeds assist in moving fresh solvent to the surface of the solute.
How do we determine the amount of solute dissolved in a solvent? To answer this question, we look at
the terms SATURATED, UNSATURATED, AND SUPER SATURATED. A saturated solution holds the
maximum amount of dissolved solute. A solution holding anything less than the amount of solute
required to be saturated is called unsaturated. Under the
proper conditions, a saturated solution can be forced to hold
more dissolved solute. In this case, the solution is said to be
super saturated. A common tool for determining saturation
points is a saturation curve.
On a more quantifiable note, we must look at the amount of
solute dissolved in terms of concentration.
CONCENTRATION is the amount of solute dissolved in a
given amount of solution or solvent. SOLUBILITY is another
term often used to describe concentrations. The most
common methods used to measure concentration are
MOLARITY and MOLALITY.
MOLARITY (M) is the number of moles of solute per 1
liter of solution. It can be expressed as moles/liters.
MOLALITY (m) is the number of moles of solute per 1
kilogram of solvent. It can be expressed as
moles/kilogram.