Mixing and Separating
In everyday life you would only come across
a few pure substances e.g. sugar, pure
water, pure gold and helium gas. Most
products that you use are a mixture of two
or more substances e.g. lipstick, soft drink
A “Gold” one dollar coin is actually made
from a mixture of copper, aluminium and
Chemical and Physical changes
Chemical reaction – new substance is
formed. These reactions are not easily
reversed e.g. wood burning.
Physical change – no new substances
are formed. These reactions can be
easily reversed e.g. ice melting.
An example of crystallisation is when you
separate sugar from water in a soft drink.
You heat the soft drink and the water
evaporates while the sugar crystallises.
• Solution – when one substance is
dissolved in another (chocolate milk)
• Solvent – substance in which the
chemical dissolves (milk)
• Solute – substance that is dissolved
in the solvent (chocolate)
• Soluble – substances which dissolve in a
liquid are said to be soluble.
• Concentrated – when more solute is
dissolved in a solvent the solution
becomes more concentrated.
• Saturated – when no more solute is able
to be dissolved in the solvent the solution
• Substances which do not dissolve in
a solvent are insoluble in that
• Sand is insoluble in water. The sand
settles to the bottom of the water
forming a sediment.
• When the insoluble substance is
dispersed (spread) throughout the
liquid, it is called a suspension.
There is a limit to the amount of solute
that will dissolve in a solution.
When a solution will dissolve no more
solute, it is saturated.
Until it reaches this point, it is
Most solids are more soluble in warm
water than in cold water. We say that
their solubility increases as the
• Decanting: gently pouring off a liquid,
leaving the solid in the container.
• Example - You gently tip the saucepan so
that the water runs out, leaving the peas in
Centrifugation: separate mixtures by a
Filtration: a way of separating a solid
from a liquid (or gas) using a filter.
This is similar to separating sand and
gravel using a sieve.
The solution that passes through the filter
paper and collects in the beaker is called the
The solid material that remains in the filter
paper is called the residue.
Once a solute has dissolved in a solvent
to form a solution, you cannot separate it
The solution simply passes through the
filter paper in the same way that water
If a solution consists of a solid dissolved in
water, you can separate them by heating.
• The water evaporates — turns into a
vapour and seems to disappear into the
air — leaving the solid behind. Salt can be
obtained from sea water by this method.
If you want to keep the liquid you must trap it
as it evaporates and condense it back to a
liquid. This process is called distillation.
Distillation can also be used to separate two
or more liquids with different boiling points,
e.g. water and alcohol.
1. If one solid is soluble in water and the
other is insoluble, you can add water.
When you filter the mixture, the residue is
the insoluble solid. The filtrate contains the
soluble solid in solution. It can be recovered
2. If one solid is attracted to a magnet
and the other is not, you can use
Used in mining.
3. If one insoluble solid floats on water and
the other sinks, you can add water to the
mixture and skim off the floating solid.
You can separate sawdust and sand this way.
4. If one solid is heavier than the other, you
can use gravity separation.
A good example of this is gold panning. Here the
water is swirled about in the pan, allowing the
heavy gold to sink and the lighter mud and sand
to be washed off the top.