SEPARATING MIXTURES AND PURE SUBSTANCES
Chemistry it is very important to be able to create pure chemical substances.
These are some of the methods tha Chemists use to separate mixtures of chemicals
and to create pure substances.
of separating insoluble solids from liquids
For separating insoluble solids with heavy particles from liquids. e.g. mixture
of sand and water.
For separating insoluble solids with fine particle from liquids e.g. mixture of
chalk powder and water.
method: For separating fluids of different densities (e.g. cream
from milk) or liquids from solids in suspensions.
of separating soluble solids from liquids
(e.g. sodium chloride from water).
distillation: Used when both solid and liquid is to be recovered.
For separating soluble solids from liquids by allowing them to form crystals.
crystallisation: For separating two or more solutes with different
solubilities at the same temperature form a liquid.
of separating coloured substances in solution
Uses the difference in rates of movement of solutes over a porous medium like
filter paper by a moving solvent (e.g. ink, chlorophyll, dyes, and so on).
of separating liquid – liquid mixtures
funnel: For immiscible liquids (e.g. paraffin and water).
distillation: For miscible liquids with boiling points widely
distillation: For separating miscible liquids with closely related
boiling points (e.g. petrol and paraffin, ethanol and water).
of separating solid-solid mixtures
Used when one of the solids sublimes on heating (e.g. iodine and sand).
Used when the mixture consist of and any other substance.
picking and winnowing: Used when the solid particles of one of
the solids are big (e.g. husks/chuff and rice).
of drying solids
between filter papers.
with drying agents.
You should be prepared to work in groups with peers under minimal supervision
of your teacher (s). Ensure that you carefully follow instructions and guidelines
provided. Attempt to observe ALL laboratory safety precautions.
experiments should help you learn some basic concepts on uniform and non uniform
mixtures, miscible and immiscible liquids, soluble and insoluble solids, solute
and solvent. You are required to mix various substances and separate them:
Mineral water bottle, knife or razor blade.
Other requirements: Toilet paper, cotton cloth, cotton wool, grass.
muddy water from a nearby well or tap drainage system.
a mineral water bottle into two parts, with the top part acting as a filter funnel.
Turn the upper part upside down and stuff it with cotton wool. Place this on top
of the other part of the mineral water bottle.
Were you successful in obtaining a clean filtrate?
Name an application
of filtration at home.
2. Sodium chloride and water by evaporation.
Metal can, charcoal stove (sigiri), paraffin stove and spoon.
requirements: Common salt, water,
some water into the metal can and add three spoonful of common salt. Stir the
mixture with the spoon until the salt dissolves.
the can on a charcoal stove and heat the solution until it evaporates to dryness.
out the salt crystals onto a paper and allow your students to taste it.
3. Parrafin and water
Separating funnel and beakers.
Other requirements: Cooking
oil or paraffin and water.
some water into a separating funnel followed by some paraffin or cooking oil.
the tap so that the water runs out.
the tap when the water level is just at the top of the tap.
the paraffin or cooking oil into a separate beaker.
How can the water be purified?
4. Alcohol and water
Distillation kit, conical flasks or mineral water bottles, bumping stones, thermometer,
tripod stand, wire gauze, rubber corks and rubber tubing.
Other requirements: Ethanol and water.
a mixture of ethanol and water into a round bottom flask and drop a few bumping
stones into the flask.
up the distillation apparatus.
the mixture until it boils.
the distillate in a conical flask.
What did you collect as the distillate?
What is the purpose of the
What was the temperature on the thermometer?
Name one economic activity that is carried out locally in the villages or town
suburbs using ideas from this method.
5. Iron and sulphur.
Other requirements: Iron filings and powdered
a little iron filings on a paper, add powdered sulphur to it and mix them.
a magnet over the mixture.
What did you observe? What substance was attracted by the magnet?
6. Ammonium chloride and sand (Sublimation)
Glass beaker, conical flask, wire gauze, tripod stand, spoon or spatula and heating
Other requirements: Water, ammonium chloride
a mixture of ammonium chloride and sand in the glass beaker.
some cold water into the conical flask and place the flask on top of the beaker.
the mixture in the beaker and observe what collects at the bottom of the conical
What substances collected at the bottom of the flask?
Name one other
substance that could be used in place of the one collected.
7. Copper(II) sulphate solution (Evaporation and
Glass beaker, heating source, wire gauze,
Copper(II) sulphate solution.
some copper(II) sulphate solution into the glass beaker.
the beaker and solution onto the wire gauze and heat it till crystals begin to
the contents in the beaker to cool.
off the crystal or filter them off, wash with a little water and dry.
What is the colour of the substance that crystallized out?
did you obtain?
Name three different methods of drying salts.
8. Separation of the components of chlorophyll using ethanol as solvent
Mortar, pestle, glass rod, beaker, office pin or wire, filter paper,
ruler and razor blade.
Other requirements: Leaves and
some leaves in a mortar and grind them. Add some ethanol to the leaves and grind
a glass rod place a drop or two of the green colouring on a rectangular piece
of filter paper. Leave the drop to dry.
a little ethanol in a glass beaker and suspend the filter paper in the beaker.
The drop must not be submerged in the ethanol in the beaker.
the set up to stand for some (15) minutes.
What did you observe? How many coloured spots do you see?
method of paper chromatography used in this experiment?
Filter muddy water using filter paper and various materials as filter paper( e.g.
cotton wool, cotton cloth, grass etc ).
Distillation of local alcohol.
funnel: Separation of a mixture of cooking oil and water.
Separation of a mixture ammonium chloride and sand.
copper(II) sulphate solution.
Copper(II) sulphate crystals from copper(II) sulphate solution.
Chlorophyll using ethanol as solvent.
Separation of a mixture of iron filing and copper turnings.
Name one method that can be used to separate the mixture of the following substances;
chloride and chalk powder
dyes in sun –sip straw berry drink.
chloride and aluminum chloride
filing and ash.
oxide and copper(II) sulphate
- Copper(II) sulphate and water.
Name two drying agents?
Explain how you can separate a mixture containing sodium chloride, ammonium
chloride and chalk powder.
State the difference between the following;
and immiscible liquids
and boiling point
The picture below shows a local distillation set up.
is the role of the copper tube?
is the tube made of copper and not plastic?
is the tube coiled in the middle?
Name separation apparatus you can see in the pictures below.
What is the effect of impurity on melting and boiling points of substances?
FOR TASK 1
(i) Filtration then evaporation
(iv) Use of Separating funnel
(v) Fractional distillation
(vii) Dissolution in water and filtration and later crystallization
sulphuric acidAnhydrous calcium chloride
mixture is first heated where the ammonium chloride escapes off as vapour (sublimes).
The remaining solid mixture of sodium chloride and chalk is now then shaken with
water to dissolve all the sodium chloride. This mixture is then filtered.
The filtrate which is sodium chloride solution is then evaporated carefully in
an evaporating dish. The residue is chalk.
4. (i) Solute is a substance that dissolves in a solvent
Miscible liquids have a homogenous layer while immiscible liquids are separated
by a clearly defined boundary.
(iii) Filtrate is obtained by filtration process
while a distillate is obtained by distillation process.
point occurs at lower temperature than boiling point. Melting point
is defined as the temperature at which a solid substance changes to liquid state
at atmospheric pressure. Boiling point is the temperature at which the vapour
pressure of the substance equals the atmospheric pressure.
To convey alcohol vapour from the drum to the collection point.
It is resistant to decomposition by heat.
(iii) To increase the surface
area for condensation of the alcohol vapour.
6. Distillation and centrifuge.
7. Impurities decrease or increase melting and boiling points.
EXTENSION WORK AND STUDENT’S PROJECTS
individual projects are intended to help you apply basic chemistry concepts and
skills acquired in class to separate mixtures and pure substances. You are
required to formulate your own procedures for carrying out the project.
Then, you will write a report about your project that may include name of project,
apparatus and procedures used, results obtained, and conclusions. You will hand
in your report to the teacher. Your work may be displayed in class for your peers
Outlined below are some of the possible individual projects you will
oil from seeds: Roast groundnuts or Simsim, pound, grind them, boil with
water until oil floats then decant off the oil.
sand filter beds.
filter funnels from plastic bottles and large leaves.
distillation kit using clay.
of copper(II) sulphate crystals.
forest made growing crystals of different chemicals in glass water.
of dyes in coloured sweets, sodas and a mixture of phenolphthalein and methyl
This activity will
help you learn how the basic principles/methods of separating mixtures and pure
substances are carried out in real world situations such as factories, laboratories,
distilleries, and sewage treatment plants. During the study tour, carry with you
pencils and notebooks for taking notes. Be prepared to ask relevant questions
to the staff at the facility visited. You may ask your teacher for help in formulating
the relevant questionnaire.
examples of facilities that operate on the principles of separating mixtures and
pure substances include:
National water and sewage treatment plants (e.g. Bugolobi sewage treatment plant
and Gaba Water Treatment plant in Uganda).
distillation: Manufacture of oxygen at Uganda Oxygen Limited (UOL)
Uganda distilleries Luzira- Kampala and Kenya petroleum refinery Mombasa.
Chemotherapeutic research laboratories( e.g. Chemotherapeutics research laboratory
Wandegeya- Kampala Uganda
Clinical laboratories (e.g. in hospitals).
of methods of separating mixtures
Sewage and water treatment (stone and sand filter beds).see pictures attached.
distillation: Production of local alcohol e.g Kasese-Kasese, Lira-Lira.
distillation: Petroleum refinery, manufacture of spirits and separation
of liquid air into oxygen and nitrogen.
separation: Used in clinical laboratories separate blood into cells (corpuscles)
crystallisation: Used in the extraction of sodium chloride (common
salt) from Lake Magadi in Kenya and Lake Katwe in Uganda.
Used in analysing chemicals e.g. plant extracts in chemotherapeutics research