The Identification of Matter
Matter
Can it be physically separated?
NO
YES
Pure Substance
Can it be chemically decomposed?
NO
Element
Mixture
Is the composition uniform?
YES
Compound
NO
YES
Heterogeneous
Are the particles visible?
NO
Colloid
Homogeneous
YES
Suspension
Solution
Review of Pure Substances
There are two types of pure substances:
1. Elements
Elements are composed of one kind of atom.
Examples are on the periodic table.
2. Compounds
Compounds are composed of two or more elements
chemically combined in a fixed ratio
When the atoms of the elements combine chemically
they form molecules of a compound
Examples: H2O, NaCl, C2H5OH, Fe2O3
Examples of atoms of elements forming
molecules of compounds
A.
B.
A. One carbon atom and one oxygen atom make
one molecule of carbon monoxide
B. One carbon atom and two oxygen atoms make
one molecule of carbon dioxide
Examination of Mixtures
There are three types of mixtures:
1. Solutions
Uniformly mixed, homogeneous mixtures of two or
more pure substances
2. Suspensions
Heterogeneous mixtures of two or more pure substances
in which the substances are visible with the naked eye
3. Colloids
Heterogeneous mixtures of two or more pure substances
in which the particles of the substances are too small to be
seen with the naked eye, but separate out over time.
Examples of Solutions:
An aqueous solution of copper sulfate
(Water and copper sulfate)
The Metallic alloy - Brass
( a mixture of copper and zinc)
Other examples:
air (mixture of gases)
water and ethyl alcohol
water and oxygen gas
An aqueous solution of potassium dichromate
(Water and potassium dichromate)
All solutions have a solute and a solvent
When a solid is dissolved in a liquid, the solid is termed the solute,
the liquid the solvent.
When one liquid is dissolved in a second liquid, the liquid present in the
smaller amount is usually called the solute. (the same for a gas in a gas)
Solutions always have a concentration
The concentration can be expressed as a solute to solvent ratio
For example:
If 5.0 grams of table salt (solute) is completely dissolved in
100 mL of water (solvent)
The concentration of the aqueous salt solution = 5.0 g/100 mL
Depending on the concentration, liquid solutions can be:
1. Unsaturated
In an unsaturated solution more solute may be
dissolved in the solvent at a given temperature
2. Saturated
In a saturated solution no more solute can be
dissolved in the solvent at a given temperature
3. Supersaturated
In a supersaturated solution more than the predicted
normal maximum amount of solute has been dissolved.
A supersaturated solution can be created when a liquid
solution is heated and then slowly cooled.
Liquid solutions can be separated physically
by using evaporation
A solution heated in an evaporation dish
Heterogeneous Mixtures - Suspensions
Examples of heterogeneous mixtures and suspensions
(note: suspensions have a liquid or gas component)
oil and vinegar - a suspension (if shaken)
sand and water - a suspension (if shaken)
iron, sulfur and salt - a solid heterogeneous mixture
Certain rocks are
solid heterogeneous
mixtures
A rock is formed from a number of substances mixed heterogeneously
Suspensions in liquids have two or more visibly obvious
components, in which, the components can be separated
physically by filtration or decantation
Filtration
Decantation
Heterogeneous Mixtures - Colloids
Examples of Colloids:
milk
shaving cream
mustard
mayonnaise
jello
fog
pearls
marshmellows
The particles in colloids are in between the size of those
in solutions and those in suspensions.
Colloids look homogeneous, but are not.
Liquid colloids will separate out slowly over time.
Colloids are often opaque, which means, you can not
see through them.
But sometimes liquid colloids can be clear and can
be confused or mistaken for a solution!
If one is not sure, there is a way to find out.
By using something called
The Tyndall Effect
The Tyndall Effect
The Tyndall Effect is used with gas and liquid mixtures.
It is a method by which a clear solution and a clear colloid
Can be identified.
Light is passed through the unknown liquid or gas mixture.
Since Light bounces off of particles, the greater the particle
size the more light will be seen.
If the reflected light is visible to the naked eye, then the
mixture is considered to be a colloid
The Tyndall Effect
light source
colloid
solution
(or a pure liquid)
http://www.silver-lightning.com/tyndall/
The laser light travels through the solution with little or no
reflection of light, while the beam is very obvious in the colloid.
A Comparison of Liquid Mixtures
solution
suspension
colloid
homogeneous
heterogeneous
heterogeneous
Very tiny particles do
not settle out
Larger particles settle
out quite quickly
Particles larger than
those in a solution
will eventually settle
out
No Tyndall effect
Tyndall effect
Tyndall effect
No separation by
filtration or
decantation
Separation by
filtration or
decantation
No separation by
filtration or
decantation
A Comparison of Mixtures and Compounds
Mixture
Compound
1.
Components may be in any proportion
Components are in fixed proportions
2.
Individual components retain their own
properties
Individual components lose their
identities. A new set of properties result
3.
Components may be separated by
physical means
Components may only be separated by
chemical means
4.
When mixed there is little, if any
evidence of a chemical change.
When combined there is evidence of a
chemical change (heat, light, gas
production, precipitate).
5.
It is a physical combination of pure
substances
It is a chemical union of atoms of
elements, to form molecules of
compounds
Identify the following as:
element, compound, solution, suspension, colloid
peanut butter
steel
nitrogen
ketchup
ethanol
whipped cream
air
cement
oil and water
salt water
lithium
sand and ethanol
water
carbon
milk
carbon dioxide
water and vinegar