Substances used for mixture State of substances used for mixture 2. Cold drink concentrate and water Observations: Describe the mixture according to a) appearance; b) colour; and c) clarity. Mixtures can be separated in different ways. 2.2 Methods of separation Particles of the different substances in the mixtures do not have the same properties. Therefore, they can be separated. The method that is used depends on the properties of the different substances in the mixture. A mixture of oil and water is called an emulsion. 54 Doc Scientia - Natural Sciences and Technology - Grade 6
We will look at a few methods: Hand sorting Separation of mixtures Evaporation Sifting Magnetism Settling and decanting Filtration Separating funnel Watch this! I suffer from separation anxiety. Doc Scientia - Natural Sciences and Technology - Grade 6 55
Jumbo 2.2.1 Hand sorting Hand sorting is used where different substances consist of larger particles and can be sorted easily by hand or by using tweezers. The particles are picked up one by one and separated from each other. Diamonds are separated from other rocks. Eggs are sorted according to size. On fruit farms, fruit, like apples and grapes are sorted by hand according to quality. Watch this! La rge 2.2.2 Sifting This method can be used when one substance has much larger particles than the other substance. Sieves have different size holes. The mixture is poured into the sieve and shaken or vibrated so that the particles that are small enough fall through. Examples: Sieve to separate rocks and sand. Small coins can be sorted using a sieve with different size holes. Fruit can be sorted by size using a sieve. Watch this! Wwwhhheeeeeeeeeeee!!! 56 Doc Scientia - Natural Sciences and Technology - Grade 6
2.2.3 Settling and decanting Mixtures that consist of liquid and solid particles that are not soluble can be left to settle. The liquid is poured off carefully. This way it separates. Examples of where settling is used: limewater where the lime settles at the bottom after it has been standing for a while; muddy water turns clear after the mud settles. What is decanting? A liquid and an insoluble solid are separated by pouring off the liquid after the solid has settled. The solid remains. Watch this! 2.2.4 Separating funnel Certain liquids do not mix with each other. Examples of this are milk and cream or oil and water. This method can be used when liquids do not mix. After the liquids have been standing for a while, one liquid floats on top of the other. The liquid with the lower density floats on top of the liquid with the higher density. Doc Scientia - Natural Sciences and Technology - Grade 6 57
Why does one liquid float on top of the other? The spaces between the particles and the masses of the particles differ. The larger the spaces between the particles of the liquid and the lower the mass of its particles, the less dense it is. It will then float on a liquid with smaller spaces and heavier particles. The bottom liquid can be drained carefully. mixture of two liquids with different densities that cannot mix (water + olive oil) mixture is poured into a funnel with a tap (a separating funnel) higher density liquid settles at the bottom the tap is opened to let out the high density liquid tap is closed as soon as the low density liquid gets to the spout 2.2.5 Filtration This is used when one of the substances is a liquid and the other is an insoluble solid. The liquid mixture is poured into the filter so the liquid can flow through, and the solid remains in the filter. Filter coffee can be divided into coffee and coffee grounds by filtration. Uuuuurrrrrmm... Excuse me... Examples: Tea made with tea leaves and then poured through a sieve. A swimming pool filter separates leaves from the water. Sand and water can be separated in this way. Curry powder and water can be separated using this method. 58 Doc Scientia - Natural Sciences and Technology - Grade 6
mixture of water and sand filter paper residue filter funnel filtrate 2.2.6 Magnetism This separation method can be used if one of the substances in the mixture can be attracted by a magnet. The other substance in the mixture must not be magnetic. I thought I tasted something strange... Magnetic means that the substance is attracted by a magnet. Doc Scientia - Natural Sciences and Technology - Grade 6 59
Magnetic substances are iron, cobalt and nickel. You will learn more about this in the coming years. The following sketches show how a magnet can be used to remove paperclips from sand. mixture of sand and paperclips hover a magnet over the surface of the mixture magnet attracts the paperclips, leaving the sand in the bowl Examples: Iron filings can be removed from other substances. Iron staples can be taken out of paper and recycled. In a scrapyard, magnetic metals can be removed and separated from others. 2.2.7 Evaporation Watch this! Evaporation is used if one substance is dissolved in another and only one of the two substances can evaporate. The liquid will evaporate. After evaporation, the solid will remain as crystals. If the mixture is heated, the liquid will evaporate faster. A crystal necklace definitely suits a saltwater fish better! 60 Doc Scientia - Natural Sciences and Technology - Grade 6
This is a simple representation of a solution of water and table salt that is heated so evaporation can occur faster. Table salt crystals are left behind. solution of water and salt solution is heated to boiling point for the liquid to evaporate solid particles of salt remain after liquid evaporates Examples: Recovering of salt from sea water Sugar is manufactured in this way from the juice of sugar cane. Mmmmmmmmmmmm Hehehehehe Evaporation is the change of a liquid into a gas at the surface of the liquid, at any temperature. Doc Scientia - Natural Sciences and Technology - Grade 6 61