Mixtures & Solutions
Objectives
 Compare the properties of suspensions, colloids,
and solutions.
 Identify types of colloids and types of solutions.
 Describe the electrostatic forces in colloids.
A heterogeneous mixture is a mixture that does not
have a uniform composition and in which the individual
substances remain distinct.
The individual substances retain their individual chemical
properties.
They are not blended smoothly through the mixture.
The two types of heterogeneous mixtures are suspensions &
colloids.
Suspensions are mixtures containing particles that
settle out if left undisturbed. Suspensions can also be
separated by filtering.
Examples are muddy water and some kinds of clay.
Some suspensions separate into a solidlike mixture on the bottom and water
on the top.
When the solid-like mixture, if stirred
or agitated, flows like a liquid, it is said
to be thixotropic.
Some substances that behave this way
are toothpaste and paint.
Colloids are heterogeneous
mixtures of intermediate sized
particles (between 1 nm and 1000
nm) that do not settle out, nor can
they be filtered apart.
The most abundant substance in a
mixture is called the dispersion
medium.
Milk is a colloid. Its dispersion
medium is a liquid.
Colloids are categorized according to the phases of the
particles dispersed in the dispersion medium.
Milk is considered an emulsion because its dispersed
particles are a liquid like its dispersion medium.
See the table on pg. 477 in the text (next slide).
The particles in a colloid do not
settle out because they often have
charged or polar structures.
These particles attract the
opposite charge of dispersingmedium particles. Electrostatic
layers work to keep the particles
suspended.
Brownian motion is the jerky, random movements of
particles in a liquid colloid, from the results of particle
collisions.
These erratic movements were first observed by Robert
Brown (1773-1858), who noticed the movement of pollen
grains dispersed in water.
Brownian motion results from collisions between the
dispersing-medium particles and the dispersed particles.
Concentrated colloids are often cloudy or opaque but dilute
ones may appear as clear as a solution.
However, dispersed colloid particles will scatter light, no
matter how dilute the colloid.
The Tyndall effect is the scattering of light by dispersed
colloid particles.
The Tyndall effect can be
used to determine the
concentration of colloid
particle.s
Solutions are homogeneous mixtures that contain two
or more substances called the solute and solvent.
The solute is the substance that dissolves. The solvent
is the dissolving medium.
It is not possible to distinguish the solute from the
solvent by appearance. It is also not possible to separate
the solute from the solvent by filtration.
 Most solutions are liquids, but gaseous and solid
solutions exist.
 The state of the solvent determines the type of
solution.
 In aqueous solutions, the solvent is water.
See text pg. 479
 A substance that dissolved in
a solvent is said to be
soluble in that solvent.
 A substance is insoluble if . .
.
 For a liquid in a liquid
solution, two substances that
are soluble in each other are
miscible.
 Immiscible means . . .