5. Separation of Substances
Introduction: In our daily life, there are many instances when we notice a substance being separated from a mixture of materials. Tea leaves are separated from the liquid with a strainer. Grain is separated from stalks, while harvesting.
Methods of Separation
1. Handpicking: Used to separate slightly larger sized impurities like the pieces of dirt, stone, and husk from wheat, rice or pulses. The quantity of such impurities is usually not very large.
2. Threshing: The process that is used to separate grain from stalks etc. Stalks are beaten to free the grain seeds. Sometimes done with the help of bullocks or machines.
ACTIVITY 3: Winnowing
Method: Used to separate heavier and lighter components of a mixture by wind or by blowing air. Example: Separating husk (lighter) from grain seeds (heavier). Ideally done in open ground.
3. Sieving: Allows the fine flour particles to pass through the holes of the sieve while the bigger impurities remain on the sieve. Used when components of a mixture have different sizes.
Sedimentation, Decantation and Filtration
Sometimes, it may not be possible to separate components by winnowing and handpicking.
- Sedimentation: When the heavier component in a mixture settles after water is added to it.
- Decantation: When the water (along with the dust) is removed.
- Filtration: Using a filter (like a piece of cloth or filter paper) to separate finer impurities. E.g., Separating tea leaves, or pulp from juice.
ACTIVITY 5: Separating Muddy Water
Process: Collect muddy water. Allow it to stand (Sedimentation). Pour clear water into another glass (Decantation). If still muddy, use a filter paper (Filtration) to get clear water.
Evaporation and Condensation
- Evaporation: The process of conversion of water into its vapour. This process takes place continuously wherever water is present. Sea water contains salts mixed in it. Salt is obtained by evaporation of sea water in shallow pits (lagoons).
- Condensation: The process of conversion of water vapour into its liquid form. Example: Water drops on a lid covering a hot pan.
ACTIVITY 7: Salt and Sand
Method: Mix salt and sand. Add water. Sand settles (Sedimentation). Decant water. Now water has salt. Heat water to evaporate it. You get salt!
Can Water Dissolve Any Amount of a Substance?
Saturated Solution: A solution in which no more substance can be dissolved at that temperature.
Tip: Heating the solution can help dissolve more substance!
SOLVED IN-TEXT QUESTION: Paheli
Q: Paheli asks if we have a mixture of salt and sugar, how can we separate them?
Ans: This is tricky for Class 6! But generally, we use alcohol (ethanol) because sugar dissolves in alcohol but salt does not. (Note: Only water is discussed in this chapter, so usually this question implies using sieving if crystal sizes differ, or just identifying them).
Chapter Summary
- Handpicking, winnowing, sieving, sedimentation, decantation and filtration are some of the methods of separating substances from their mixtures.
- Husk and stones could 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 the process of 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.
- Filtration can be used to separate components of a mixture of an insoluble solid and a liquid.
- Evaporation is the process in which a liquid gets converted into its vapour. Evaporation can be used to separate a solid dissolved in a liquid.
Exercise Q1
Q: Why do we need to separate different components of a mixture? Give two examples.
Examples:
- Separating stones from rice.
- Churning milk to obtain butter.
Exercise Q2
Q: What is winnowing? Where is it used?
Exercise Q3
Q: How will you separate husk or dirt particles from a given sample of pulses before cooking?
Exercise Q4
Q: What is sieving? Where is it used?
Exercise Q5
Q: How will you separate sand and water from their mixture?
Exercise Q6
Q: Is it possible to separate sugar mixed with wheat flour? If yes, how will you do it?
Exercise Q7
Q: How would you obtain clear water from a sample of muddy water?
Exercise Q8: Fill in the blanks
- Method of separating seeds of paddy from its stalks is called Threshing.
- 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 Filtration.
- Salt is obtained from sea water by the process of Evaporation.
- 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 Decantation.
Exercise Q9: True or False
- A mixture of milk and water can be separated by filtration. (False)
- A mixture of powdered salt and sugar can be separated by the process of winnowing. (False)
- Separation of sugar from tea can be done with filtration. (False) (Sugar dissolves)
- Grain and husk can be separated with the process of decantation. (False) (Winnowing)
Exercise Q10
Q: Preparation of Lemonade: ice before or after dissolving sugar?
Key Facts and Definitions
- Churning: Process of shaking milk or cream to separate butter.
- Saturated Solution: A solution in which no more solute can be dissolved.
- Solution: A homogeneous mixture of two or more substances (Solute + Solvent).
| Technique | Principle | Example |
|---|---|---|
| Handpicking | Visible difference in size/color | Stones from rice |
| Winnowing | Difference in weight | Grain and husk |
| Sieving | Difference in size | Flour and bran |
| Sedimentation | Heavier particles settle | Mud settling in water |
Miscible Liquids: Liquids that completely soluble in water (e.g. Alcohol, Vinegar).
Immiscible Liquids: Liquids that do not dissolve in water (e.g. Oil, Petrol) and can be separated by Decantation (or Separating Funnel).