1. Natural Sciences Grade 7
Term 2: Matter and Materials
Separating mixtures
(ppt 2)

2. Topic 2 Separating mixtures
Methods of physical separation
Natural Sciences - Grade 7

3. Natural Sciences - Grade 7
Hand sorting
Sorting by hand (according to physical properties of size, colour, texture and shape).
It is cheap and easy, but it can take a long time.
Prior to fruit being sent to the market, it is hand sorted and packed according to quality and size.
Hand sorting was the first method used in the history of waste sorting.
Waste segregation means the waste is divided into dry (wood, glass, metal, etc. ) and wet waste.
Coarser mined materials can make the hand-sorting work much easier.
Hand-sorting in small-scale underground mines in developing countries frequently occurs.
 The hand-sorting operation can be improved and increase efficiency if cleaner material, better lighting, etc. are provided at the separation tables / sorting belts.
Children and unemployed adults are often found sitting among piles of garbage busy hand-sorting the refuse.
Mountains of brightly coloured plastic are hand-sorted by shade and type.
Natural Sciences - Grade 7

4. Hand sorting - examples
Thorns from sheep’s wool (after shearing, the fleece is cleaned and the thorns are removed);
Beans from rice;
Beads from buttons;
Nuts from bolts and screws;
Paper clips from safety pins;
Rice from lentils; etc.
Natural Sciences - Grade 7

5. Natural Sciences - Grade 7
Sieving [1]
Sieving is a method used to separate:
- two solids that have particles of different sizes
- a liquid from a solid
Sieves have holes that are all of the same size.
Sieves allow small particles / liquids to pass through the holes
The bigger particles [solids] are too big and it cannot pass through the sieve’s holes so it remains in the sieve.
A sieve used for sifting flour has very small holes.
The mesh in a wooden sieve is made from wood or wicker.
A strainer is a form of a sieve that is used to separate solids from liquid.
It is important to sift flour because:
- sifted flour is lighter than unsifted flour
- it is easier to mix into the other ingredients of a cake batter or when making dough
- it helps to combine the dry ingredients evenly
- the baked goods will have a lighter texture
- it adds air to the flour
- it is the key to successful baking
Natural Sciences - Grade 7

6. Natural Sciences - Grade 7
Sieving [2]
In the past, tea strainers (small sieves) were used to pour the tea leaves that were mixed with boiling water through it. Presently teabags (made from a paper-like material), are used and it works as a filter.
Kitchen sieves are also used
to strain cooked rice / pasta
and to sift cake flour.
Natural Sciences - Grade 7

7. Natural Sciences - Grade 7
Sieving [3]
Gold diggers use a special sieve
to separate gold nuggets from
the sand and water.
Natural Sciences - Grade 7

8. Natural Sciences - Grade 7
Sieving [4]
Before the builders can use the sand to make plaster, they use industrial size sieves to separate the sand from the stones and other impurities.
Natural Sciences - Grade 7

9. Natural Sciences - Grade 7
Using a magnet [1]
Magnets can attract iron (Iron, nickel and cobalt are magnetic elements).
The difference in the properties makes it possible to separate a magnetic substance that is mixed with a non-magnetic (aluminium and copper) substance.
Plastic and glass (non-metals),
are not attracted to magnets.
A magnet has two ends called poles (south pole and north pole)
The north pole of one magnet attracts the south pole of a second magnet
The north pole of one magnet repels the other magnet's north pole.
A magnet creates an invisible area of magnetism all around it (magnetic field).
Magnetization (Running a magnet a few times over an un-magnetized piece of a magnetic material (iron nail), can change it into a magnet as well.
Magnetic fields cut through paper (placing reminders with a magnet against the refrigerator's door)
A magnet can be used to pick up a long chain of paperclips.
Every electric appliance with an electric motor in it (electric toothbrush, lawn mower, etc. ) uses magnets to turn electricity into motion.
Magnets:
- in refrigerators hold the doors closed.
- read and write data (digital information) on a computer's hard drive.
- in the hi-fi loudspeakers / headphones help to turn stored music back into audible sounds.
- are used to recycle metal trash (picture 4)
Natural Sciences - Grade 7

10. Natural Sciences - Grade 7
Using a magnet [2]
Magnetic substances are recovered from domestic ways to be recycled by using magnets.
Magnets can sort iron nails from broken glass and iron filings from sand and salt.
Natural Sciences - Grade 7

11. Natural Sciences - Grade 7
Evaporation [1]
Salt can be retrieved out of the sea water by evaporation.
The process of separating a mixture by turning the liquid / solvent part (water)into a gas (water vapour), is called evaporation.
The crystals of salt (solutes) are left behind when salt water evaporates.
South Africa produces less than 50% of its salt requirements.
The shortfall (40% ) of salt is imported from Botswana, Australia and Namibia.
Sources of Salt in S.A come from: 20% Sea water; 77% Inland Salt pans and 3% Coastal salt pans.
Two methods of salt production are used in South Africa: .,
- Method 1: Pure vacuum dried (PVD) salt is produced at Coega, near Port Elizabeth
- Method 2: Solar evaporation of brines from inland and coastal saltpans.
The weather is an important factor in salt production:
- sunshine is beneficial
- wind helps evaporation but it may also cause contamination
- rainfall dilutes solutions
- storms may damage crystallisation ponds.
Methods have been developed to improve solar evaporation (installing sprinklers that produce fine mist / droplets).
There are 16 operating salt companies in South Africa that include one cooperative operation with more than 40 small-scale producer members.
The biggest producer is Upington Super Salt , followed by Swartkops, Saltcor, Industrial Salt, Cerebos and Orange River Salt Works.
Natural Sciences - Grade 7

12. Natural Sciences - Grade 7
Evaporation [2]
The Cerebos salt factory in Coega, near Port Elizabeth, retrieves the salt from sea water, which is held in shallow evaporating pans, by evaporation.
The salt is produced for commercial use.
The energy to evaporate water from the salt pans, is provided by the wind and the sun.
Salt can eventually be collected after the water had become more salty from moving through a series of ponds.
South Africa produces less than 50% of its salt requirements.
The shortfall (40% ) of salt is imported from Botswana, Australia and Namibia.
Sources of Salt in S.A come from: 20% Sea water; 77% Inland Salt pans and 3% Coastal salt pans.
Two methods of salt production are used in South Africa:
- Method 1: Pure vacuum dried (PVD) salt is produced at Coega, near Port Elizabeth
- Method 2: Solar evaporation of brines from inland and coastal saltpans.
The weather is an important factor in salt production:
- sunshine is beneficial
- wind helps evaporation but it may also cause contamination
- rainfall dilutes solutions
- storms may damage crystallisation ponds.
Methods have been developed to improve solar evaporation (installing sprinklers that produce fine mist / droplets).
There are 16 operating salt companies in South Africa that include one cooperative operation with more than 40 small-scale producer members.
The biggest producer is Upington Super Salt , followed by Swartkops, Saltcor, Industrial Salt, Cerebos and Orange River Salt Works.
Natural Sciences - Grade 7

13. Natural Sciences - Grade 7
Distillation [1]
Distillation (evaporation followed by condensation) is used to collect the solute as well as the solvent when a solution is separated.
The solution is heated. The solvent evaporates and the vapour is collected when the solution is heated.
The vapour is cooled so that it condenses and becomes a liquid.
Pure water can be collected from sea water through the process of distillation.
Distillation is commonly used to separate ethanol (alcohol in alcoholic drinks ) from water. 
Some liquids decompose (break apart) at / below their boiling points. 
Presently 95 % of all separation processes are carried out in industry with more than 40,000 distillation systems. 
A petroleum refining plant is usually distinguished by a group of distilling towers that rise more than 30 meters into the air. 
Distillation is used to :
- distil alcohol and produce distilled beverages (it is illegal to distil alcohol without a license and it is called moonshine)
- separate various fuels and raw materials from crude oil in the oil industry
- separate diesel, petrol, paraffin and LPG gas from crude oil
Natural Sciences - Grade 7

14. Natural Sciences - Grade 7
Distillation [2]
When salt water is heated in a pot, the water evaporates from the solution and eventually it condenses on the pot’s lid.
The distillation process needs a lot of heat energy which makes it very expensive.
Distillation makes it possible to separate the mixture of two liquids with different boiling points, e.g. mixture of water [100°C] and ethanol – [78,37°C].
Distillation is commonly used to separate ethanol (alcohol in alcoholic drinks ) from water. 
Some liquids decompose (break apart) at / below their boiling points. 
Presently 95 % of all separation processes are carried out in industry with more than 40,000 distillation systems. 
A petroleum refining plant is usually distinguished by a group of distilling towers that rise more than 30 meters into the air. 
Distillation is used to :
- distil alcohol and produce distilled beverages (it is illegal to distil alcohol without a license and it is called moonshine)
- separate various fuels and raw materials from crude oil in the oil industry
- separate diesel, petrol, paraffin and LPG gas from crude oil
Natural Sciences - Grade 7

15. Distillation [3] Liebig condensers
Distillation is commonly used to separate ethanol (alcohol in alcoholic drinks ) from water. 
Some liquids decompose (break apart) at / below their boiling points. 
Presently 95 % of all separation processes are carried out in industry with more than 40,000 distillation systems. 
A petroleum refining plant is usually distinguished by a group of distilling towers that rise more than 30 meters into the air. 
Distillation is used to :
- distil alcohol and produce distilled beverages (it is illegal to distil alcohol without a license and it is called moonshine)
- separate various fuels and raw materials from crude oil in the oil industry
- separate diesel, petrol, paraffin and LPG gas from crude oil
Natural Sciences - Grade 7

16. Natural Sciences - Grade 7
Chromatography [1]
The special substances that give colour to living tissues, paint, ink and specific materials, are pigments.
Pigments are responsible for the dye used in certain fabrics, as well as the red colour in blood.
There is more than one pigment in the ink of pens.
Chromatography is used to separate a mixture of different pigments.
Certain pigments dissolve easier than others.
Natural Sciences - Grade 7

17. Natural Sciences - Grade 7
Chromatography [2]
Alcohol / Water can be added as a solvent to a mixture of pigments and it can travel through paper.
Colours of the different pigments that were used to make ink can be identified as follows:
less soluble pigments covers a short distance through the paper, because it travels slower.
more soluble pigments covers a longer distance through the paper, because it travels faster.
Natural Sciences - Grade 7

18. Natural Sciences - Grade 7
Chromatography [3]
An example of paper chromatography.
Natural Sciences - Grade 7