Questions and Answers
Why do we need to separate different components of a mixture?
To remove harmful or non-useful substances, and to use useful components separately.
What is winnowing?
Winnowing is a method used to separate heavier and lighter components of a mixture using wind.
How will you separate husk or dirt particles from a given sample of pulses before cooking?
By washing the pulses in water and allowing the impurities to settle or by handpicking.
What is sieving, and where is it used?
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How will you separate sand and water from their mixture?
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Is it possible to separate sugar mixed with wheat flour? If yes, how will you do it?
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The method of separating seeds of paddy from its stalks is called __________.
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How would you obtain clear water from a sample of muddy water?
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When milk, cooled after boiling, is poured onto a piece of cloth, the cream (malai) is left behind on it. This process of separating cream from milk is an example of __________.
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Salt is obtained from seawater by the process of __________.
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Impurities settled at the bottom when muddy water was kept overnight in a bucket. The clear water was then poured off from the top. The process of separation used in this example is called __________.
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A mixture of powdered salt and sugar can be separated by the process of winnowing.
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A mixture of milk and water can be separated by filtration.
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Separation of sugar from tea can be done with filtration.
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Grain and husk can be separated with the process of decantation.
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Should you add ice to the lemonade before or after dissolving sugar? In which case would it be possible to dissolve more sugar?
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Study Notes
Separation of Substances
- In our daily life, we often need to separate substances from a mixture of materials.
- Examples: separating tea leaves from liquid, butter from milk or curd, grain from stalks, and salt from a mixture.
Handpicking
- Handpicking is a convenient method of separating slightly larger impurities from a substance.
- Example: separating stones, husks, and broken grains from wheat, rice, or pulses.
Threshing
- Threshing is a process used to separate grain seeds from stalks.
- Example: farmers use threshing to separate grain from stalks, and machines are also used to thresh large quantities of grain.
Winnowing
- Winnowing is a method of separating heavier and lighter components of a mixture by wind or by blowing air.
- Example: farmers use winnowing to separate lighter husk particles from heavier seeds of grain.
Sieving
- Sieving is used to separate components of a mixture based on their sizes.
- Examples: separating pebbles and stones from sand, and removing impurities from flour.
- Sieving is commonly used in flour mills to remove impurities like husk and stones from wheat.
Sedimentation, Decantation, and Filtration
- Sedimentation is the process of separating heavier components from a mixture that settle at the bottom of a container.
- Decantation is the process of pouring out the top layer of a mixture, leaving the heavier components behind.
- Filtration is the process of separating components of a mixture based on their ability to pass through a filter.
- Examples: separating rice or pulses from impurities like dust or soil particles, and separating water from insoluble impurities like soil.
Evaporation
- Evaporation is the process of converting water into its vapour.
- Evaporation can be used to separate a mixture of water and salt.
- Example: sea water is evaporated to obtain salt, and common salt is then obtained from this mixture of salts by further purification.
Condensation
- Condensation is the process of converting water vapour into its liquid form.
- Example: steam from a kettle condenses into liquid water when it comes into contact with a cooled surface.
Uses of More than One Method
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Often, one method of separation is not sufficient to separate the different substances present in a mixture.
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In such cases, more than one method is used to separate the substances.
- Example: separating salt, sand, and water using processes of decantation, filtration, evaporation, and condensation.### Separation of Substances
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Substances can dissolve in water and form a solution, and many substances are soluble in water.
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If we go on adding more and more of a substance to a fixed quantity of water, a point will be reached where the solution becomes saturated, meaning no more of that substance can be dissolved in the water.
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Water cannot dissolve an unlimited amount of a substance, and the amount it can dissolve varies from substance to substance.
Dissolving Salt in Water
- When dissolving salt in water, if we go on adding salt, one teaspoonful at a time, and stir, eventually the solution will become saturated, and no more salt can be dissolved in the water.
- If we heat a saturated solution of salt in water, more salt can be dissolved in it.
- Once the hot solution cools, the salt appears to settle at the bottom of the beaker again.
Solubility of Different Substances
- Water dissolves different amounts of different soluble substances, as shown in Table 3.2.
- For example, salt and sugar are both soluble in water, but they dissolve in different amounts.
Methods of Separating Substances
- Handpicking: separating husk and stones from grains.
- Winnowing: separating husk from heavier seeds of grain.
- Sieving: separating particles of different sizes in a mixture.
- Decantation: separating sand and water from their mixture.
- Filtration: separating components of a mixture of an insoluble solid and a liquid.
- Evaporation: separating a solid dissolved in a liquid.
Applications of Separation Methods
- Sieving is used in separating components of a mixture of different sizes.
- Filtration is used in separating components of a mixture of an insoluble solid and a liquid.
- Evaporation is used in separating a solid dissolved in a liquid.
Separation of Substances from Mixtures
- Husk and stones can be separated from grains by handpicking.
- Husk is separated from heavier seeds of grain by winnowing.
- Difference in the size of particles in a mixture is utilised to separate them by sieving and filtration.
- In a mixture of sand and water, the heavier sand particles settle down at the bottom and the water can be separated by decantation.
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Description
Separation of substances from mixtures in daily life, such as tea leaves and butter
