Separation of Substances

In our daily life, we often separate substances from mixtures. Here are some common examples:

Tea leaves are separated from the liquid using a strainer when making tea.
Grains are separated from stalks during harvesting.
Butter is separated from milk or curd by churning.
Cotton seeds are separated from the fiber using a process called ginning.

Imagine you have a basket of mangoes and guavas. To separate them, you would pick out each type and place them in different containers. Easy, right? But what if the substances are much smaller, like sand mixed with salt? You can’t separate them by handpicking.

Methods of Separation

We use different methods to separate substances based on their properties. Let’s look at a few:

Handpicking

Activity: (click here)

Activity: Bring a packet of food grain to the classroom. Spread the grains on a sheet of paper. You might find stones, husks, and other impurities.
Method: Use your hands to remove these impurities.

Usage: This is useful for larger impurities in grains like wheat, rice, or pulses.

Threshing

What It Is: After harvesting, stalks of crops like wheat or paddy are dried in the sun. Each stalk has many grain seeds.
Method: Stalks are beaten to free the grain seeds.
Tools: Threshing can be done by hand, using bullocks, or with machines.
Usage: Separates grains from stalks.

Winnowing

Activity:

Mix dry sand with sawdust or powdered dry leaves. Look at the mixture—can you separate it by hand? No.
Method: Take the mixture to an open ground. Hold it high and let it slide out slowly. The wind will blow away the lighter sawdust, leaving the heavier sand behind.

Usage: Farmers use this to separate lighter husk particles from heavier grain seeds. The wind carries away the husk, and the seeds form a heap.

Summary

Handpicking: Used for large impurities.
Threshing: Separates grains from stalks by beating.
Winnowing: Uses wind to separate lighter and heavier components.

Sieving

Purpose: To remove impurities and bran from flour.
How It Works:
- Pour flour into a sieve.
- Fine flour particles pass through the holes.
- Bigger impurities stay on the sieve.
Examples:
- Flour Mills: Remove husk and stones from wheat before grinding.
- Construction Sites: Separate pebbles and stones from sand.

Activity:

Bring flour to class, sieve it to remove impurities. Mix powdered chalk with flour and try to sieve them. Sieving works when components have different sizes.

Sedimentation, Decantation, and Filtration

Purpose: To separate lighter impurities like dust or soil from rice or pulses, and to separate insoluble impurities from water.
Sedimentation:
- Add water to rice or pulses.
- Heavier impurities sink to the bottom.
- Example: Dust particles in rice sink when water is added.
Decantation:
- Tilt the vessel to pour out the water (with impurities).
- Example: Pouring out water after sedimentation to remove dust.
Filtration:
- Pour the mixture through a filter.
- Tea strainer example: Strain tea to remove leaves.
- Use cloth or filter paper for finer filtration.
- Examples:
  - Muddy Water: Let soil settle (sedimentation), pour out water (decantation), and use a filter to remove remaining impurities.
  - Juices: Filter to remove seeds and pulp.
  - Paneer: Filter milk after adding lemon juice to separate paneer from liquid.

Activity:

Collect muddy water, let it settle, and pour the clear water into another glass (sedimentation and decantation). Use a cloth or filter paper to filter out remaining impurities.

Summary

Sieving: Separates particles of different sizes.
Sedimentation and Decantation: Separates heavier impurities by settling and pouring out water.
Filtration: Uses filters to remove fine impurities.

Evaporation

Purpose: To separate a mixture of water and salt.

Activity:

Add salt to water and stir.
Heat the mixture until water boils away.
Salt is left behind in the beaker.

Definition: Evaporation is the process of turning water into vapor.
Example:
- Sea Water: Sunlight heats sea water in shallow pits, water evaporates, and salt is left behind.
- Common salt is obtained by purifying the leftover salt mixture.

Using More Than One Method

Sometimes, one method isn’t enough to separate substances. Multiple methods are needed.

Activity: Separating Sand and Salt

Steps:
1. Mixing: Combine sand and salt in a beaker.
2. Adding Water: Add water to the mixture and let it sit.
3. Settling: Sand settles at the bottom.
4. Decantation: Pour off the water to separate sand.
5. Evaporation: Boil the decanted water in a kettle.
6. Condensation: Hold a metal plate with ice above the kettle spout to collect condensed water.
7. Result: Salt remains in the kettle after all water evaporates.

Key Processes:
- Decantation: Separates sand from the water.
- Evaporation: Turns water into vapor, leaving salt behind.
- Condensation: Turns steam back into liquid water.
Example:
- Milk: Water drops under a plate covering boiled milk are due to condensation.

Problem Solving

Paheli’s Issue: Mixed salt with sand but recovered only a small part using these methods.
Possible Problem: Not all salt dissolved or was properly evaporated and condensed.

Summary

Evaporation: Used to separate dissolved substances from water.
Multiple Methods: Sometimes necessary to fully separate mixtures.
Key Techniques: Decantation, filtration, evaporation, and condensation.

These methods help us use substances safely and efficiently by removing unwanted materials.

Can Water Dissolve Any Amount of a Substance?

Solubility in Water

Soluble Substances: Many substances dissolve in water to form solutions.

Activity:

Add salt to water gradually.
Stir until no more salt dissolves.
When salt stops dissolving and settles at the bottom, the solution is saturated.

Saturation

Saturated Solution: No more of the substance can dissolve in the water.
Example:
- Paheli’s Problem: She mixed too much salt with sand, and the salt did not fully dissolve because the solution became saturated.
- Solution: Use more water to dissolve more salt.

Increasing Solubility

Activity:

Activity:
- Create a saturated salt solution.
- Heat the solution.
- Observe that more salt dissolves when heated.
- Cool the solution to see if salt settles again.
Observation: Heating increases water’s ability to dissolve more salt.

Concept: Heating increases water’s ability to dissolve more salt.

Different Substances, Different Amounts

Activity:

Compare how much salt and sugar dissolve in separate glasses of water.
Record the number of teaspoons needed to saturate each solution.

Observation: Water dissolves different substances in different amounts.

Concept: Water dissolves different substances in different amounts.

Summary

Solubility: Substances dissolve in water to form solutions.
Saturated Solution: No more substance can dissolve in the water.
Heating: Can dissolve more of a substance in water.
Different Substances: Water dissolves varying amounts of different substances.

These concepts help us understand how substances mix with water and how we can manipulate conditions to dissolve more.

Chapter Summary:

Handpicking, winnowing, sieving, sedimentation, decantation, and filtration are methods of separating substances from mixtures.
Husk and stones can be separated from grains by handpicking.
Husk is separated from heavier seeds of grain by winnowing.
The size difference of particles in a mixture is used for sieving and filtration.
In a mixture of sand and water, heavier sand particles settle at the bottom, and water can be separated by decantation.
Filtration separates components of a mixture with an insoluble solid and a liquid.
Evaporation is when a liquid turns into vapor.
Evaporation can separate a solid dissolved in a liquid.
A saturated solution cannot dissolve more of the substance.
More of a substance can dissolve in a solution by heating it.
Water dissolves different amounts of soluble substances.

Keywords

Serial No.	Keyword 1	Serial No.	Keyword 2
1	Churning	7	Saturated solution
2	Condensation	8	Sedimentation
3	Decantation	9	Sieving
4	Evaporation	10	Solution
5	Filtration	11	Threshing
6	Handpicking	12	Winnowing

Keywords

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