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๐ฌ Think about it
Break a piece of chalk in half. Break it again, and again. Grind it to powder. Each speck is still chalk. But could you keep breaking forever? Like splitting a chocolate bar into tinier and tinier bits, there must be a smallest piece. Let's discover it.
What happens when we keep breaking and grinding chalk?
- Each tiny grain is still a speck of chalk.
- Grinding only reduces the size — it is a physical change.
- The chalk does not turn into a new substance.
- Imagine grinding on and on until pieces cannot break further.
Example:
Grinding chalk is a physical change, like tearing paper into smaller bits.
In this Activity, we will keep breaking and grinding chalk to see how small its pieces can get.
Materials needed
A stick of chalk, a mortar and pestle, a magnifying glass.
Procedure
1. Take a stick of chalk and break it into two pieces.
2. Continue breaking the chalk till it is difficult to break further by hand.
3. Grind the small pieces using a mortar and pestle.
4. Observe the fine chalk powder with a magnifying glass.
5. Note what each tiny grain looks like.
2. Continue breaking the chalk till it is difficult to break further by hand.
3. Grind the small pieces using a mortar and pestle.
4. Observe the fine chalk powder with a magnifying glass.
5. Note what each tiny grain looks like.
Observation
Each tiny grain you observe is still a speck of chalk.
Explanation
Grinding chalk is a physical change. The chalk does not become a new substance — only the size of each speck reduces. If we kept grinding, we would reach the smallest units that chalk is made of.
โ Summary
- Chalk broken small
- Ground to powder
- Still chalk
- Physical change
What are constituent particles?
- Keep grinding and chalk reaches its smallest building blocks.
- One piece of chalk is made of a huge number of these units.
- These tiny units are called constituent particles.
- Sand and clay grains are also made of constituent particles.
Example:
Like bricks in a wall, constituent particles are the smallest units that build up chalk.
In this Activity, we will dissolve sugar in water to see how it breaks into particles we can no longer see.
Safety first
Perform under the supervision of a teacher or adult. Never eat or drink anything unless asked to.
Materials needed
A glass tumbler, drinking water, two teaspoons of sugar, a spoon.
Procedure
1. Fill a glass tumbler with drinking water.
2. Put two teaspoons of sugar into it.
3. Do not stir the water; taste a small spoonful from the top layer.
4. Now stir the water until the sugar dissolves completely.
5. Again taste a spoonful of water from the top layer.
6. Note any difference in taste, and look for sugar particles.
2. Put two teaspoons of sugar into it.
3. Do not stir the water; taste a small spoonful from the top layer.
4. Now stir the water until the sugar dissolves completely.
5. Again taste a spoonful of water from the top layer.
6. Note any difference in taste, and look for sugar particles.
Observation
Before stirring, the top is not sweet. After dissolving, the top layer tastes sweet, but no sugar particles can be seen.
Explanation
The sweet taste shows sugar is present even though we cannot see it. When sugar dissolves, it breaks up into its constituent particles, which cannot be broken further. Each grain of sugar is made of millions and millions of such particles.
โ Summary
- Sugar added to water
- Stirred to dissolve
- Water tastes sweet
- Particles too small
Where does the dissolved sugar go?
- Matter is made of a large number of extremely small particles.
- They are too tiny to see, even through an ordinary microscope.
- Sugar particles fill the gaps between the water particles.
- These gaps are called interparticle spaces.
Example:
Sugar particles slip into the spaces between water particles, like sand filling gaps between marbles.
Important Points
- Matter is made of a very large number of extremely small particles.
- The smallest building units are called constituent particles.
- There are gaps between particles, called interparticle spaces.
โ Test Yourself
-
Is grinding chalk a physical or chemical change?
View Answer
A physical change. Only the size of the chalk reduces — it does not turn into a new substance. -
What is a constituent particle?
View Answer
The basic smallest unit that makes up a larger piece of a substance or material. -
Why does dissolved sugar taste sweet but stay invisible?
View Answer
It breaks into constituent particles too small to see, but the taste tells us it is still there. -
What are interparticle spaces?
View Answer
The empty gaps between the particles of matter. Sugar particles fit into the gaps between water particles. -
Can constituent particles be seen with a microscope?
View Answer
No, they are so small they cannot be seen even through an ordinary microscope.
Important Definitions
- Constituent particle — the basic unit that makes up a larger piece of a substance or material.
- Interparticle spaces — the empty spaces between the particles of matter.
๐ NCERT Question 3 — Choose the correct answer
If all the constituent particles were removed from a chair, what would happen to it?
View Answer →
๐ NCERT Question 9 — Why does the water
Why does ocean water taste salty even though the salt is not visible? Explain.
View Answer →
