Unit 1: Pure Substances and Mixtures
What are things made of?
Matter is anything that has mass and takes up space.
We can see and feel most types of matter.
We can classify items in many different ways (for example: soft,
hard, shiny, colourful, liquid, solid).
To make products, we mix new materials together in combinations
that may require heating, freezing, stirring, melting, hardening or
dissolving.
Through a series of processes, we end up with the items we use
every day.
The raw materials that we use for products come from the earth
(for example: the food we grow, metals we mine).
By taking things from the earth and putting things into landfills, we
are having an effect on the environment.
Classifying Substances
Matter is defined as anything that has mass and volume.
Mass usually refers to the amount of stuff in a substance.
Volume indicates the amount of space a substance occupies.
Matter generally exists in three forms: solid, liquid, and gas.
A fourth state does exist: plasma. Substances may be classified
according to their physical, chemical and biological properties.
Physical properties include: size, shape, texture, mass, volume
Chemical properties refer to the way substance reacts with other
substances to form new substances.
Biological properties refer to characteristics of life such as
metabolism, growth, irritability, locomotion, reproduction, and
adaptation.
Pure Substances
A pure substance contains only one kind of particle throughout.
Only a few pure substances can be found in nature. Almost all
pure substances we use have been made pure by humans. We take
the raw material that contains them and separate out the substance
we want. (e.g. table sugar, aluminum foil)
Mixtures
Almost all substances (natural and man-made) are mixtures of pure
substances.
Mechanical Mixtures and Solutions
Pure substances mix to form either mechanical mixtures or solutions.
Solution: particles of the pure substances are mixed evenly so that
neither original substance is visible. (e.g. chocolate milk)
(also called a homogeneous mixture)
pure substance
solution
pure substance
In a solution, one substance has mixed completely, or dissolved,
into another. They look like pure mixtures, but contain at least two
different kinds of particles.
Solvent: the substance into which they dissolve (has large spaces in
the particles)
Solutes: the substances that dissolve (has small spaces in the
particles). When combined with the solvent, the solute hides in the
larger spaces of the solvent.
complete chart using info on p 21:
Solution
Solutes
Solvent
Air
oxygen, argon, carbon dioxide
nitrogen
Steel
oxygen, carbon
iron
Juice
sugar, minerals,
water
Types of Solutions
Example
Solute
Solvent
air (hydrogen in oxygen)
gas
gas
pop (carbon dioxide in water)
gas
liquid
antifreeze (alcohol in water)
vinegar (acetic acid in water)
liquid
liquid
dental fillings
amalgams
liquid
solid
salt or sugar in water
solid
liquid
brass (copper in zinc)
solder (tin in lead)
alloys like steel (carbon in iron)
solid
solid
Mechanical Mixture: the substances do not mix evenly. Both
substances are clearly visible and can be separated.
(e.g. granola, or sand and rocks)
(also called a heterogeneous mixture)
pure substance
mechanical mixture
pure substance
Particle Theory
Solid: particles are close together and
locked into a pattern. They can move,
but only back and forth a little.
Attractive forces hold the particles
together.
Liquid: particles are slightly farther apart.
Because the particles are farther apart,
the attractive forces are weaker.
They are able to slide past one another.
Gas: particles are far apart. The particles
can move in any direction because
the attractive forces are weakest.
Types of Mixtures
Suspension: A solid and a liquid which
mix but settle upon
standing, such as silt and
water.
Emulsion: Two liquids which mix but separate
upon standing, such as oil and water.
Colloids: mixtures that are made of particles of one substance
suspended into another. The suspended particles get
stuck in the spaces of the other particles. This allows
them to scatter light. (e.g. smoke in air)
Colloids will show the Tyndall Effect.
Tyndall Effect: shows that some mixtures that appear to be
solutions may prove not to be solutions after all. If the
path of light shining through a mixture can easily be
seen, then that mixture is not a solution. A non-solution
contains particles large enough to
scatter or reflect light, showing the
path of light as it passed through a
mixture. True solutions do not show
the Tyndall Effect.
Solutions
Colloids
Suspensions
Homogeneous
Heterogeneous
Heterogeneous
Do not separate on standing
Do not separate on
standing
Particles settle out
Cannot be separated by
filtration
Cannot be separated by
filtration
Can be separated by
filtration
Do not scatter light
Scatter light (Tyndall
effect)
May scatter light, but are not
transparent
Separation of Mixtures
Solutions and mechanical mixtures can be separated in many ways.
1. Evaporation: the liquid evaporates and a solid
(residue) is left behind.
2. Distillation: a two step process that:
a) heats a solution to change one part into gas and then,
b) cools the gas/vapour to liquid form and collects it
3. Filtration: the use of a funnel and filter paper to
separate a solid from a liquid. The liquid
passes through the filter paper and is called
filtrate. The solid remains in the filter paper
and is called residue.
4. Sifting: using a sieve, different sized substances can
be separated.
5. Magnetism: a magnet can be used to remove metal
from non-metallic substances.
Mechanical Mixtures and Solutions
Problem
To create and identify a variety of mechanical mixtures and
solutions.
Materials
• test tubes
• rubber stoppers
• test tube rack
• water
• salt
• sugar
•
•
•
•
•
rice
flour
drink crystals
ethanol
graduated cylinder
Method
Part A:
1. Label 10 test tubes with numbers 1 through 12.
2. In each of the test tubes 1-6, pour 20 mL of water.
3. Add a pinch of solute to each test tube.
4. Stopper each tube.
5. Shake.
Part B:
6. Put 20mL of ethanol in each.
7. Repeat steps 3-6.
8. Dispose of the contents of the test tubes as instructed by teacher.
9. Clean up.
Observations
See chart.
Analysis and Interpretation
1. Which of the substances seemed to “disappear” when mixed in
a) water?
b) ethanol?
2. Which of the substances were you still able to see (even after
vigorous shaking) in
a) water?
b) ethanol?
Looking Back / Conclusion
The solids that I think will settle to the bottom when the mixture is
left overnight are _________________________________
because ________________________________.
Inquiry Observations
Mechanical Mixtures and Solutions
Name: _________________________
Mixture
Solute
Solvent
1
Salt
Water
2
Sugar
Water
3
Rice
Water
4
Flour
Water
5
Drink Water
Crystals
6
Salt
Ethanol
7
Sugar
Ethanol
8
Rice
Ethanol
9
Flour
Ethanol
10
Oil
Water
11
Drink Ethanol
Crystals
12
Oil
Colour
Clear or
Cloudy?
Are Particles Mechanical
Present?
Mixture?
Solution?
Ethanol
Sub Task 1: Mixtures & Solutions
How Do Solutions Form?
Some substances mix easily to form solutions, while others do not
mix at all. If a solution is formed, particles in the solute are
attracted to particles of the solvent and break apart to attach to the
solvent particles in the spaces between them. This means the
solute is soluble, or able to be dissolved. The resulting volume
may not be the sum of the two volumes before combined. (e.g.
water & alcohol)
A Model for a Solution
50 mL water + 50 mL dice
=
If the particles of the solute are not attracted to the particles of the
solvent, the two substances generally cannot form a solution. This
means that the solute is insoluble, or unable to be dissolved.
The Rate of Dissolving
Many factors affect the speed at which one substance dissolves in
another, for example:
•
•
the surface area of the solute particles
size of the solute particles
Breaking up the solute particles into smaller pieces increases the
overall surface area of crystals exposed to solvent, thereby
accelerating the dissolving process.
•
temperature
As temperature increases, the particles move faster and spread out
with greater chances for mixing of the solute and solvent particles.
•
•
•
amount of solute
amount of solvent
amount of shaking
The greater the amount of solvent relative to the solute, the greater
the opportunity for interactions and attractions between the solute
and solvent particles, and the more uniform the distribution of the
particles.
•
type of solvent
The level of attraction changes with the types of particles.
Dissolving will happen faster when the solute’s and solvent’s
particles are highly attractive.
Saturated or Unsaturated?
Concentration: the amount of solute dissolved in a given quantity
of solvent or solution.
Dilute Solutions: low concentration of
solute (“weak”)
Concentrated Solutions: high amount of
solute (“strong”)
Unsaturated Solutions: still contain unfilled spaces between the
solvent particles
Saturated Solutions: the maximum amount of solute dissolved in
the solution (all the spaces in solvent are filled). If you try to
strengthen a saturated solution, the solute will simply sink to the
bottom of the solvent without dissolving.
Supersaturation: a solution that contains more of the solute than
would be found in a saturated solution (can be made with some
solutes by starting with a hot saturated solution and cooling it
slowly).