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๐ฌ Think about it
Try squashing a balloon full of air — it shrinks. Try squashing a bottle of water — it barely moves. The gaps between particles are big in gases but tiny in liquids and solids. Let's measure these gaps with simple experiments.
Why can a gas be compressed but a liquid cannot?
- Pushing a syringe plunger reduces the volume of air inside.
- Gas particles have a lot of space between them.
- This space can be reduced by pressure.
- Water has tiny gaps, so it is practically incompressible.
Gas (air)
Liquid (water)
Large interparticle spaces.
Very small interparticle spaces.
Easily compressed by pressure.
Practically incompressible.
Plunger pushes in a lot.
Plunger hardly moves.
In this Activity, we will compress air in a syringe to show that gases have large spaces between their particles.
Materials needed
A syringe without a needle; water (for the repeat).
Procedure
1. Take a syringe without a needle and pull the plunger fully out.
2. Place your thumb over the open end so the air cannot escape.
3. Push the plunger slowly and steadily inwards.
4. Observe what happens to the volume of air.
5. Stop pushing and watch the plunger move back.
6. Repeat the activity using water instead of air.
2. Place your thumb over the open end so the air cannot escape.
3. Push the plunger slowly and steadily inwards.
4. Observe what happens to the volume of air.
5. Stop pushing and watch the plunger move back.
6. Repeat the activity using water instead of air.
Observation
The air volume decreases when pushed and springs back when released. With water, the plunger barely moves — water is practically incompressible.
Explanation
Gas particles have a lot of space between them, so pressure pushes them closer and reduces the volume. Releasing lets them spread again. Water particles have very little space, so water cannot be compressed.
โ Summary
- Air pushed in
- Volume decreases
- Water won't compress
- Gases have space
In this Activity, we will dissolve sugar in water and watch the level to show that liquids have spaces between their particles.
Materials needed
A glass vessel, water, two teaspoons of sugar, a glass rod, a marker.
Procedure
1. Fill a glass vessel about half with water and mark the level as A.
2. Add two teaspoons of sugar into it.
3. Mark the new water level as B.
4. Stir with a glass rod to dissolve the sugar.
5. Predict whether the level will rise or fall from B.
6. Mark the final water level as C.
7. Repeat with salt or glucose, and with insoluble sand or stone.
2. Add two teaspoons of sugar into it.
3. Mark the new water level as B.
4. Stir with a glass rod to dissolve the sugar.
5. Predict whether the level will rise or fall from B.
6. Mark the final water level as C.
7. Repeat with salt or glucose, and with insoluble sand or stone.
Observation
Adding sugar first raises the level (B), but after dissolving the level drops (C). The solution volume is less than water plus sugar separately.
Explanation
Since the solution volume is less than the sum of water and sugar, there must be spaces between the water particles. The dissolved sugar particles occupy these spaces. Insoluble sand does not dissolve; it settles and adds to the volume.
โ Summary
- Sugar added, level rises
- Stirred to dissolve
- Level drops
- Spaces in water
Why does sugar dissolve in water but sand does not?
- Sugar breaks into particles that fit between water particles.
- So the sugar disappears into the water.
- Sand particles are held too strongly to be pulled apart.
- So sand settles down and increases the volume.
Example:
Stir sugar and it vanishes; stir sand and it just sinks to the bottom.
How does interparticle spacing differ across the three states?
- Solids have the smallest spaces; particles are closely packed.
- Liquids have a little more space than solids.
- Gases have the largest spaces of all.
- The gaps contain nothing at all — not even air.
Interparticle Spacing: Solid to Gas
Solid
Smallest spacing; particles closely packed.
↓
Liquid
A little more space than in solids.
↓
Gas: maximum spacing
๐ก A step further
- The word "particle" means different things in different contexts.
- In air pollution, "Suspended Particulate Matter (SPM)" means tiny dust.
- These dust particles are not the constituent particles of matter.
- Even dust particles are made of huge numbers of atoms and molecules.
Important Points
- Gases compress easily; liquids and solids barely compress.
- Dissolved particles fit into the spaces between liquid particles.
- Spacing grows from solid to liquid to gas; the gaps hold nothing.
โ Test Yourself
-
Why is air easy to compress?
View Answer
Gas particles have large spaces between them, so pressure pushes them closer and reduces the volume. -
Is water compressible?
View Answer
No, water is practically incompressible because its particles have very little space between them. -
Why does the level drop after sugar dissolves?
View Answer
Sugar particles fit into the spaces between water particles, so the solution takes up less space than the two separately. -
Which state has the largest interparticle spaces?
View Answer
Gases have the largest spaces. Solids have the smallest, and liquids are in between. -
What fills the gaps between particles in a solid?
View Answer
Nothing at all. The gaps are not filled with air — they contain nothing.
Important Definitions
- Suspended Particulate Matter (SPM) — tiny dust particles suspended in air, much larger than constituent particles.
- Incompressible — something whose volume cannot be reduced by pressure, like water.
๐ NCERT Question 7 — Draw a picture representing
Draw the particles present in aluminium foil, glycerin, and methane gas.
View Answer →
๐ NCERT Question 8 — Observe Fig. 7.16a which
Identify the different states of wax in an extinguished candle and match them to particle arrangements.
View Answer →
