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A. Fill in the blanks
- Housewives sometimes use the method of hand picking to remove unwanted substances from eatables like rice and pulses.
- Common salt is prepared on a large scale through the process of evaporation.
- Separation of tea leaves from tea is done by a process called filtration.
- The process of loading can be used to increase the rate of sedimentation of the suspended particles in a solid-liquid mixture.
- The method used to separate the fine particles suspended in a liquid by rotating the mixture at high speed is known as centrifugation.
B. Match the following
| Column A | Column B |
|---|---|
| 1. Wind | (b) Winnowing |
| 2. Chalk powder and water | (c) Sedimentation |
| 3. Oil and water | (e) Separating funnel |
| 4. Separating peas from cooked pulao | (a) Hand picking |
| 5. Muslin cloth | (d) Filtration |
| 6. Camphor and salt | (f) Sublimation |
C. Tick (✓) the correct option
1. Which of the following is an example of a heterogeneous mixture?
✅ Pebbles in rice
2. Which one of the following is not an example of a pure substance?
✅ Air
3. The process of loading helps to—
✅ Speed up the rate of sedimentation
4. Transferring the clear liquid into another container, leaving behind the residue, is called—
✅ Decantation
5. A substance that sublimes easily is—
✅ Naphthalene
D. Answer the following questions in brief.
1. Name any three methods used for separating a solid-solid mixture.
Three methods used for separating a solid-solid mixture are:
- Hand picking
- Winnowing
- Sieving
These methods help us separate useful substances from unwanted materials in our daily life. Farmers, shopkeepers, and even homemakers use these simple techniques to keep food clean and safe for everyone.
2. What is winnowing? Give an example of a mixture whose components can be separated by this method.
Winnowing is the method of separating lighter particles from heavier particles with the help of wind or blowing air. In this process, the lighter particles are carried away by the wind while the heavier particles fall down near the person performing the activity.
For example, husk can be separated from grains using winnowing.
This method has been used by farmers for many years and helps in cleaning food grains naturally without harming the environment.
3. Some iron pins get scattered on the carpet when you are expecting guests. How can one collect all the pins in the shortest possible time?
The iron pins can be collected quickly by using a magnet. When the magnet is moved over the carpet, the iron pins stick to it because iron is attracted towards magnets.
This method saves time, reduces effort, and also helps in preventing injuries that may happen if someone accidentally steps on the pins.
4. Name any three substances which sublime on heating.
Three substances that sublime on heating are:
- Camphor
- Naphthalene
- Ammonium chloride
These substances directly change from solid state into vapour on heating without becoming liquid.
5. What is crystallisation? Name any three substances which can be purified using this technique.
Crystallisation is the process of obtaining pure solid crystals from a solution. It is used to purify substances by removing impurities dissolved in them.
Three substances that can be purified by crystallisation are:
- Common salt
- Sugar
- Copper sulphate
This method is very useful in laboratories and industries because it helps in obtaining clean and pure substances that are safe to use.
E. Answer the following questions.
1. Differentiate between a pure substance and a mixture. Give two examples of each.
| Pure Substance | Mixture |
|---|---|
| A pure substance contains only one kind of particle. | A mixture contains two or more substances mixed together. |
| It has fixed composition and definite properties. | Its composition may vary. |
| The components cannot be separated by simple physical methods. | The components can be separated by physical methods. |
Examples of Pure Substances:
- Distilled water
- Common salt
Examples of Mixtures:
- Air
- Salt and sand mixt
- Pure substances are uniform throughout, while mixtures are formed when substances combine physically without changing their individual properties.
2. State the difference between heterogeneous and homogeneous mixtures. Give two examples of each type.
| Homogeneous Mixture | Heterogeneous Mixture |
|---|---|
| The composition is uniform throughout. | The composition is not uniform throughout. |
| Different components cannot be seen separately. | Different components can be seen separately. |
Examples of Homogeneous Mixtures:
- Salt dissolved in water
- Air
Examples of Heterogeneous Mixtures:
- Sand and water
- Oil and water
The DAV Class 6 book explains that homogeneous mixtures appear as a single substance, whereas heterogeneous mixtures show different parts separately.
3. Can a mixture of iodine and camphor be separated by the sublimation method? Give reason for your answer.
No, a mixture of iodine and camphor cannot be separated by the sublimation method because both iodine and camphor are sublimable substances. On heating, both change directly from solid to vapour. Since both substances sublime together, it becomes difficult to separate one from the other by this method.
4. Why does the size of naphthalene balls, put in open, keep on reducing with time?
Naphthalene balls keep on reducing in size because naphthalene undergoes sublimation. It changes directly from solid state into vapour without becoming liquid. When kept in the open, the vapours mix with air continuously, so the balls gradually become smaller. This process is commonly used to keep clothes safe from insects and moths.
5. After a dust storm, how does rain help in making air clear?
Rain helps in making air clear after a dust storm because raindrops trap dust particles and bring them down to the ground. As the dust settles, the air becomes cleaner and fresher. shows a natural process of separation where heavier particles are removed from the air with water.
6. Sawdust, mixed in water, cannot be separated by the sedimentation method. Why?
Sawdust cannot be separated from water by sedimentation because it is lighter than water and floats on the surface instead of settling down at the bottom. Sedimentation works only for substances that are heavier than water. Therefore, other methods like filtration or skimming are more suitable for separating sawdust from water.
7. The filtration method cannot be used to separate sugar and salt mixed in water. Why?
Filtration cannot be used because both sugar and salt dissolve completely in water to form a solution. The dissolved particles are very small and pass through the filter paper along with water. Filtration is useful only for separating insoluble substances from liquids.
8. Describe the method of centrifugation using an appropriate example.
Centrifugation is a method used to separate heavier insoluble particles from a liquid by rotating the mixture at high speed. The heavier particles settle down at the bottom due to the spinning motion. Example: In dairies, centrifugation is used to separate cream from milk. When milk is spun rapidly in a machine called a centrifuge, the heavier portion remains below while the lighter cream collects on the top.This method is also used in washing machines to remove water from wet clothes.
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