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Separating Substances
D. Crowley, 2007
Thursday, July 6, 2017
Separating Substances
• To know how to separate substances
Key Terms
• Name the following: -
Solute
Solvent
Solution
Solution - the mixture formed when a substance dissolves in it
Solute - the substance that dissolves
Solvent - the liquid in the solution
Dissolve - mixing of a substance in a liquid
Soluble - a substance which can dissolve (mix in a liquid)
Insoluble - a substance which cannot dissolve (mix in a liquid)
Accident
• Transport company set to lose millions…
• Yesterday a large truck crashed on the Marchwood Bypass
shedding its load in the road – a representative from the
transport company commented ‘this is a catastrophe! The truck
was carrying a large amount of sand, salt and iron, all destined
for different companies…
• We do not know how we are going to fulfil these orders unless
we are able to separate the mixture – if we fail to do this, we will
lose an enormous amount of money!’
Accident
• How could you help the company separate the sand, salt and
iron – consider this in your groups…
Filtration
• How does filtration work?
• Can you and your partner come up with a good explanation?
• Filtration can separate in insoluble solid (does not dissolve) from
a liquid
What if its dissolved?
•
Some solids dissolve in liquids (soluble) – others, such as sand, are not
(insoluble)
•
What could we do to separate something which has dissolved - e.g. salt
from water?
•
Say we were stuck on a ship, out at sea, and we ran out of water - how
could we get some fresh drinking water?
Dissolved
•
•
Why can’t we use filtration for salt and water?
Think about the particles, and what happens to them when they
dissolve
•
The salt has dissolved - its particles are thoroughly mixed, so they will
just pass straight through our filter paper…
•
•
Think about the Dead Sea - remember this has a very high salt level
Rivers flow into it, but none flow out - the salt level increases, but the
water level stays pretty constant - so where is the water going, and by
what means?!
Evaporation
• The Dead Sea is so salty because no rivers flow out of it. This
means, that when the water evaporates, the salt is left behind
• Evaporation can be really useful - remember its where a liquid
changes into a gas
• Water can be evaporated, leaving our solute behind (the salt)
Risks
• Before you complete this experiment, we need to consider the
risks
• Using your risk assessment, think about the apparatus we are
going to be using, and write in the risks and action to be taken…
What will you do?
•
Tick which equipment you will need
•
Explain how you are going to carry out your experiment - how you will
separate the sand, salt, iron and water?
•
And finally, draw the equipment you are going to use for the
corresponding experiment
Experiment
• Remember all the safety rules we follow during an experiment…
• Be as accurate as possible!
• The group with most sand + salt + iron separated will be the
winners
Salt pile
Sand pile
Iron pile
Review
• How did the filtration separate the sand and water?
• How did the evaporation separate the salt and water?
• Why would filtration not separate salt from water?
• Why did the magnet remove the iron but not the salt or sand?
Filtration
•
Filtration works because the filter paper will stop the insoluble solid
from passing through it - this makes it nice and easy for us to collect!
The filter paper can easily
catch the insoluble sand
Evaporation
•
Evaporation helps us separate because some water particles are given enough
energy to escape the attraction of the other particles. If we heat the water for a
long enough, eventually all our particles are given enough energy to escape, just
leaving salt
•
Salt cannot be separated using filtration, because the particles are too well
mixed - this means that they would pass straight through the filter paper
The filter paper cannot catch the soluble
salt, as the particles are too well mixed
Magnetism
• Only some metals are magnetic, allowing this method to
separate our iron from the other substances…
Levels
• Level 4 – the student draws a diagram and simply explains what
has happened
• Level 5 – the student draws a diagram using the correct
symbols and explains filtration and evaporation using the correct
scientific terms
• Level 6 – the student draws and labels a diagram using the
correct symbols and using a ruler and pencil. The student also
explains filtration and evaporation using a particle model