Imagine you have a box of plastic counters. Some of them are green, some blue, some red and some yellow.
If each counter represented a different substance we would say we had a mixture .
We have a mixture when there is more than one substance in our container.
Example: muddy water would be a mixture. It countains mud and water
How can I separate my mixture?
Well, if we had counters it would be easy.
We would tip them all out of the box and arrange them into four piles: green counters, blue counters, red counters and yellow counters
With real substances it is more difficult to separate them.
We can make water water clean by pouring it through a filter.
The particles of mud get stuck in the holes and clear water drips through.
Four ways to separating a mixture
1. Using a sieve
A sieve is used to separate small solid particles from larger ones.
Example: using a sieve to sparate gravel (small pebbles) from sand
A sieve is a shallow tray with holes in.
The mixture is placed in the sieve which is then shaken from side to side.
The sand particles are much smaller than the gravel so fall though the holes in the sieve.
Using a sieve to separate sand from pebbles.
2. Using a magnet
Separates magnetic substances (eg substances containing iron) from non-magnetic substances.
Example: separating iron filings from sand
Picture 1: we have a mixture of iron filings and sand on a piece of paper
Picture 2: When a magnet is slowly pulled away from the mixture the iron sticks to the magnet leaving the sand behind
Using a magnet to separate iron filings from sand
Filtering is used to separate small solid particles from a liquid
Example: Separating dirt from water by filtering
The dirty water is poured through a piece of filter paper.
Water particles pass through the tiny holes in the filter paper.
The particles of dirt, which are larger than the particles of water, get stuck in the holes and do not get through.
When the process is finished the dirt is trapped in the filter paper and the clear water has dripped through into the beaker below.
Any liquid that has been filtered is known as a filtrate
Using filter paper to remove dirt from water
. 4. Evaporation
Evaporation is used when we want to get back a substance that has been dissolved
Example: Getting salt out of salty water
The salty water is put into an evaporating basin (or any shallow dish such as a saucer).
It is left in a warm place and the water evaporates leaving behind the salt crystals.
We see the salt crystals starting to form at the edge of the salty water but eventually all the water would go, leaving behind just the salt.
Evaporating water from salty water to get the salt
When we have only one substance, for example just blue counters, we say that it is pure.
Perfectly clean water is pure because it contains only water
Salty water is a mixture because it contains salt and water.
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