1st Year Science – Chemistry
Separating Mixtures – Introduction
Mixtures:
‘A mixture is made up of 2 or more substances mingled
together but not chemically combined’
e.g. Air – oxygen, carbon dioxide, Nitrogen
e.g. Cup of Coffee – coffee granules, milk, water, sugar
e.g. Sea Water– water, salt, chlorine and many more
Ways of Separating Mixtures
• Decanting: Very Basic method
• Filtration & Evaporation: Separating solids from liquids
• Distillation: Uses evaporation to separate 2 liquids
• Chromatography: Separating Different Dyes in inks
Filtration
Evaporation
Distillation
Chromatography
Separating Solids from liquids
The type of separation depends on whether the solid is Soluble or
Insoluble in the liquid
Soluble:
Solids that dissolve in liquids to form a solution
e.g. Sugar in tea or coffee, Salt in sea water
Evaporation can be used to separate
soluble solids and Liquids
Insoluble: Solids that don’t dissolve.
Instead they sink to the bottom of the liquid
e.g. Sand & soil in water
Filtration can be used to separate
insoluble solids and Liquids
Filtration Experiment
Title:
‘Separation of Soil and Water’
Apparatus:
Beaker, Stirring rod, Retort stand, Funnel, Filter paper,
Soil/water mixture
Filter paper
Filtrate
Evaporation Experiment
Title:
‘Separation of Salt and Water through Evaporation’
Apparatus:
Bunsen Burner, Tripod, Evaporating Dish, Salt water
solution, Beaker of Water (optional)
Evaporating
Dish
Salt water
Solution
Tripod
Bunsen Burner
Separating Solids from liquids
Another basic method of filtration is Decanting
Water
Water
Sand
Solids are allowed to settle at the bottom of the liquid and then
water is gently drained off.
Distillation
• The problem with evaporation is that the liquid is lost.
• Distillation is a method of separation that saves the liquid(s)
Distillation is used to separate...
1.
Two miscible liquids (liquids that mix)
e.g. Water and alcohol
2. Soluble solids from liquids
e.g. Salt and water
Two types of Distillation...
1.
Simple distillation
2. Fractional Distillation
Immiscible means substances that do not mix together e.g. Water & oil
Distillation
Simple Distillation:
e.g. Separation of two miscible liquids – Water and alcohol
• Both liquids have two different boiling points...
Round
Bottom
Flask
Water = 100⁰C
Alcohol = 78⁰C
• Some water evaporates with the
Thermometer
Water Out
Liebig Condenser
alcohol, therefore it is not a perfect
method of separation
Solution
• Cooling water condenses steam back
into water droplets (distillate)
Water In
• Can also be used to separate liquids
and solids (salt & water)
Wire
Gauze
Tripod
Bunsen Burner
Distillate
Simple Distillation
Distillation
Fractional Distillation:
• Greater quality of separation
• Fractionating column is heated to the
Fractionating Column
Thermometer
boiling point of alcohol (78⁰C)
Round
Bottom
Flask
• The water cools down over the long
Liebig Condenser
Water Out
distance and condenses back into
droplets.
Water In
• The pure alcohol continues on
Distillate
through the Liebig condenser and
Solution
condenses at the other end as
Wire Gauze
distillate.
Tripod
Bunsen Burner
Fractional Distillation
Distillation – Separating Salt and Water
Chromatography
• Chromatography is a method used to separate complex mixtures
e.g. Hospitals: Analysing blood samples
e.g. Forensics: Analysing samples from crime scenes
How Chromatography is carried out:
• A coloured dot is placed at one end of the chromatography paper
• The strip is placed in a beaker/cylinder that contains a solvent (water)
• The strip is placed in the solvent with the ink dots above solvent (water) level.
• The solvent (water) is absorbed upwards through the paper and carries the different
dyes with it
• Some dyes only go up to a certain point therefore separating them out.
Chromatography
How Chromatography is carried out:
Container
Separated Dyes
After 10-15 minutes
Chromatography
Paper
Solvent
(water)
Ink
Spots
Direction of Absorbed Solvent