Mixtures and Methods Of Separating Mixtures class 8
INTRODUCTION
In our surroundings, we see and use many materials that are made by combining two or more substances. These combinations are called mixtures. A mixture is a material made up of two or more substances (elements or compounds) that are physically combined, not chemically. This means the individual substances in a mixture retain their original properties and can be separated by physical means.
For example, when we mix salt in water, we get a saltwater mixture. Similarly, air is a mixture of gases like nitrogen, oxygen, carbon dioxide, and others. In our kitchens, we often mix different food items like pulses and stones (before cleaning), sugar in milk, or spices — all of these are mixtures.
Methods of Separation of Mixtures
A mixture is made up of two or more substances that are physically combined. Since the components are not chemically bonded, they can be separated by various physical methods. The method used depends on the physical properties of the substances such as size, shape, weight, solubility, magnetism, or boiling point. These separation techniques are used in our homes, laboratories, and industries.
Below are the commonly used methods of separation:
1. Hand Picking
2. Threshing
3. Winnowing
4. Sieving
5. Magnetic Separation
6. Sedimentation and Decantation
7. Filtration
8. Evaporation
9. Distillation
10. Crystallization
1. Hand Picking
This is one of the simplest separation methods, used when the unwanted substances are visibly different and can be picked out by hand. It is useful only when the quantity of the mixture is small.
Example: Removing small stones, insects, or spoiled grains from pulses, rice, or wheat.
Real-life use: Households use this method before cooking.
2. Threshing
Threshing is the process of separating grains from harvested plants. It can be done by beating the crop on a hard surface, by trampling under animals, or by using threshing machines.
Example: Separating wheat or rice grains from stalks.
Used by: Farmers during post-harvest processing.
3. Winnowing
This method uses the wind or blowing air to separate lighter substances from heavier ones.
Example: Separating husk (chaff) from grains.
Working principle: The wind carries the lighter husk away while the heavier grains fall straight down.
Used in: Villages and rural areas after threshing.
4. Sieving
Sieving is used when the mixture contains components of different sizes. A sieve (a mesh or net with holes) allows smaller particles to pass through while larger ones remain behind.
Example:
Separating sand from gravel
Removing husk or impurities from flour
Common in: Kitchens, construction work, and grain cleaning.
5. Magnetic Separation
When one of the substances in a mixture is magnetic (like iron), it can be separated using a magnet.
Example: Separating iron filings from a mixture of sand and iron.
Used in: Scrap industries, recycling plants.
6. Sedimentation and Decantation
In this method, the heavier solid settles at the bottom of a liquid (sedimentation), and the clear upper liquid is poured off (decantation).
Example:
Removing mud from muddy water
Separating oil from water
Used in: Water treatment plants and home water purification.
7. Filtration
This method uses a filter (such as cloth, sieve, or filter paper) to separate an insoluble solid from a liquid.
Example:
Filtering tea leaves from tea
Purifying drinking water using filters
Used in: Labs, kitchens, and water purifiers.
8. Evaporation
Evaporation is used to separate a soluble solid from a liquid. The liquid evaporates on heating, leaving the solid behind.
Example:
Getting salt from seawater
Recovering sugar from sugarcane juice
Used in: Salt-making industries, sugar mills.
9. Distillation
Distillation separates two miscible liquids with different boiling points. The mixture is heated, the liquid with the lower boiling point turns into vapor, and the vapor is then cooled and collected.
Example:
Separating alcohol from water
Purifying water
Used in: Laboratories, distilleries, and industries.
10. Crystallization
This method is used to obtain pure solid substances in the form of crystals from their solutions. It is more effective than simple evaporation as it removes impurities.
Example:
Preparing crystals of copper sulphate
Making sugar and salt crystals
Used in: Chemical labs and food industries.
Other Methods to Mention (Briefly):
Centrifugation: Used to separate tiny suspended particles by spinning the mixture at high speed.
Example: Separating cream from milk.
Churning (Butter Separation): Used to separate butter (fat) from curd by rapid stirring.
Separating Funnel: Used to separate two immiscible liquids (liquids that do not mix), such as oil and water.
Conclusion
Separation techniques help us purify substances, remove harmful impurities, and make mixtures useful. From simple handpicking to advanced distillation, each method has a special role in science and everyday life. Understanding these methods allows us to appreciate the importance of separation in homes, schools, industries, and the environment.
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