Activity 5.1 – Table of common changes
Q (a) Complete Table 5.1 – what do you observe for each change?
| S. No. | Change | Simple observation |
|---|---|---|
| 1 | Melting ice cubes | Ice becomes liquid water. |
| 2 | Chopping vegetables | Large pieces become many small pieces. |
| 3 | Boiling water | Water turns to steam (gas) and bubbles. |
| 4 | Making popcorn from corn | Hard corn pops into white fluffy popcorn and smells nice. |
| 5 | Cutting a piece of paper | One sheet becomes many parts; shape changes. |
| 6 | Adding beetroot extract to water | Water turns pink-red. |
| 7 | Burning wood | Wood turns black, gives smoke, heat and ash. |
| 8 | Drying wet clothes | Water in cloth goes away; cloth feels dry. |
| 9 | Making small balls of dough | Big lump is divided into small balls. |
| 10 | Rolling balls into chapatis | Dough balls flatten into round chapatis. |
| 11 | Any other (e.g., rusting iron) | Shiny iron gets brown rust spots. |
Activity 5.2 – Paper folding, balloon play, chalk crushing
Q 1. Do you get the same sheet of paper back after unfolding?
Yes. The paper is the same; only its shape was changed.
Q 2. Balloon questions
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After letting air out slowly, you get the original empty balloon back.
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After pricking with a pin the balloon bursts; you cannot get the original balloon back.
Q 3. Can you get the chalk piece back from the powder?
No, once crushed the chalk cannot be re-made easily at home.
Q 4. Is there any similarity in the changes A, B and C?
Yes, in all of them only the appearance (size or shape or state) changed. The material itself stayed the same. These are physical changes.
Activity 5.3 – Blowing into water and lime water
Q What do you notice?
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In tap water: only bubbles, water stays clear → no new substance.
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In lime water: bubbles plus water turns milky and later a white solid settles → a new substance formed (calcium carbonate). This is a chemical change.
Activity 5.4 – Vinegar and baking-soda
Q What do you observe when vinegar and baking soda are mixed?
Fizzing sound and many bubbles— a gas is made. If you pass this gas into fresh lime water, the lime water turns milky. So the gas is carbon dioxide. It is a chemical change.
Q Repeat with baking soda and water— any bubbles? Physical or chemical?
No big bubbles form. Only baking soda dissolves a little— this is mostly a physical change (no new substance seen).
Activity 5.5 – Candle under a tumbler
Q What happens to the two candle flames?
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The open candle keeps burning.
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The candle covered by the glass tumbler goes out after a short time.
Reason: the covered candle uses up the oxygen inside the glass; without oxygen the flame stops.
Activity 5.6 – Ignition temperature (paper + match / sun-rays)
Q What do you observe?
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Paper near a lighted match lights up immediately.
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Concentrated sun-rays first brown the paper, then it smokes and finally catches fire.
This shows a substance burns only after its temperature reaches the ignition temperature.
Activity 5.7 – Burning candle (think–pair–share)
Q What changes occur when a candle burns?
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Wax melts (solid to liquid) – physical.
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Melted wax climbs the wick and evaporates – physical.
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Wax vapour burns, making new substances (carbon dioxide, water vapour, soot) plus heat and light – chemical.
So burning a candle has both physical and chemical changes.
Activity 5.8 – Which changes can be reversed?
A sample fill for Table 5.2:
| Change | Can the original form come back? | Reason |
|---|---|---|
| Melting ice cubes | Yes | Freeze the water again. |
| Chopping vegetables | No | Pieces cannot re-join. |
| Boiling water | Yes | Cool the steam to get water. |
| Making popcorn | No | Popcorn can’t turn back into kernels. |
| … | … | … |
5.3, 5.4, 5.5 In-text questions
| Question | Answer in simple words |
|---|---|
| Is rusting physical or chemical? | Chemical – iron becomes a new brown substance (iron oxide). |
| Is burning magnesium a physical or chemical change? | Chemical – turns into white magnesium oxide plus heat & light. |
| What three things are needed for combustion? | Fuel, oxygen, heat (ignition temperature). |
| Is tearing paper desirable or undesirable? | Usually desirable when we need small pieces, undesirable if we spoil a book page. |
LET US ENHANCE OUR LEARNING – Exercise Answers
1. Choose the correct statements for a physical change.
Answer: (c) (i) and (iii).
State may change; no new substance forms.
2. Reversible or not?
| Change | Reversible? | Why |
|---|---|---|
| Stitching cloth to a shirt | No | You can’t get the same cloth pieces back easily. |
| Twisting a straight string | Yes | Untwist to original. |
| Making idlis from batter | No | New cooked substance. |
| Dissolving sugar in water | Yes | Evaporate water, sugar reappears. |
| Drawing water from a well | Yes | Water can be poured back. |
| Ripening of fruits | No | Cannot un-ripe. |
| Boiling water in open pan | Partly – steam can be cooled | Condense steam to water. |
| Rolling up a mat | Yes | Unroll it. |
| Grinding wheat to flour | No | Flour can’t be grains again. |
| Soil forming from rocks | No (very hard to reverse) | Natural very slow process. |
3. True / False
| Statement | T / F | Correction if False |
|---|---|---|
| (i) Melting of wax is necessary for burning a candle. | True | |
| (ii) Collecting water vapour by condensing involves a chemical change. | False – it is physical. | |
| (iii) Leaves turning into compost is a chemical change. | True | |
| (iv) Mixing baking soda with lemon juice is a chemical change. | True |
4. Fill in the blanks
(i) Brown deposits are due to rusting, and this is a chemical change.
(ii) Folding a handkerchief is a physical change and can be reversed.
(iii) The process is called combustion, and this is a chemical change.
(iv) Burning magnesium produces magnesium oxide. The substance formed is basic in nature. Burning of magnesium is a chemical change.
5. Are water → ice and water → steam physical or chemical?
Both are physical changes because only the state (solid, liquid, gas) changes; water itself stays the same substance.
6. Is curdling of milk physical or chemical?
Chemical change. The milk proteins change permanently, forming new substances (curd).
7. Weathering of rocks into soil – physical or chemical and why?
It is both:
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Breaking into smaller pieces = physical
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Minerals reacting with water/air = chemical
8. Story “Eco-friendly Prithvi” – choose the type of change
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Chopping/peeling: physical changes
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Collecting waste in clay pot: physical (just gathering)
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Composting: chemical change
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Seed germination and flower blooming: chemical changes
(Any suitable creative title is fine, e.g., “From Kitchen Waste to Colourful Garden.”)
9. Venn diagram of changes
| Area | Changes |
|---|---|
| A (Physical only) | Tearing paper, Melting ice, Folding clothes |
| B (Chemical only) | Rusting, Curdling milk, Ripening fruits, Mixing baking soda with vinegar, Burning magnesium |
| C (Both physical + chemical) | Burning candle |
10. Lime-water test (Fig 5.11) – where does it turn milky and why?
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(a) Vinegar + baking soda → makes CO₂ → lime water turns milky.
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(d) Lemon juice + baking soda → also makes CO₂ → lime water turns milky.
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(b) Vinegar + common salt does not make CO₂, lime water stays clear.
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(c) Lemon juice + vinegar just mixes two acids, no CO₂, lime water stays clear.