Course 2.2Lesson 1 of 3
We separate the parts of a mixture by physical means that use a difference in a property. Evaporation, filtration, centrifugation and a separating funnel are four simple methods.
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Most of the materials that we need come as mixtures. Salt is mixed with sea water. Oxygen is mixed with other gases in air. Crude oil is a mixture of many fuels. To use a part, we separate it. Sometimes we also remove a harmful part, such as a stone from rice.
The parts of a mixture have different properties, such as the size of the particles, the boiling point or the density. A method of separation uses one of these differences. It does not change the parts into new substances.
A solution of salt in water can be heated. The water evaporates, and the salt stays behind. We use this to get salt from sea water, in shallow pans in the sun. It also separates a dye from ink.
Limit. We lose the water. Some solids also decompose when heated too strongly.
When sand is mixed with water, we pass the mixture through filter paper. The water goes through the tiny holes of the paper, and the sand stays on the paper. The liquid that goes through is the filtrate. We use filters to clean water, and in a tea strainer.
Some particles are so small that they would pass through the filter paper, or take very long to settle. In centrifugation, the mixture is spun very fast in a machine called a centrifuge. The heavier particles are thrown to the bottom of the tube, and the liquid stays at the top. We can pour it off.
Examples: separating cream from milk, and the parts of blood in a laboratory. Washing machines use the same idea to spin water out of clothes.
You should find that at turns each minute the push is about a thousand times gravity, and the day-long wait shrinks to under two minutes.
Oil and water do not mix, and they form two layers. The heavier liquid (water) is at the bottom. We pour the mixture into a separating funnel. When we open the tap, the lower liquid flows out first. We close the tap when only the upper liquid is left.
When one part of a mixture sublimes and the other does not, we heat the mixture. The part that sublimes turns into a gas, and it forms a solid again on a cold surface. We use this for a mixture of ammonium chloride and sand.
| The mixture | The property that is different | The method |
|---|---|---|
| Sand and water | One part does not dissolve | Filtration |
| Salt and water | One part does not evaporate | Evaporation |
| Oil and water | They do not mix, and their densities differ | Separating funnel |
| Cream and milk | Particle size and density | Centrifugation |
| Ammonium chloride and sand | One part sublimes | Sublimation |
The program finds how much salt two shallow pans of sea water give when they dry in the sun.
Try each one on your own first. If you are stuck, open a hint. Then check with Show the answer.
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