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प्रश्न
Which of the following are chemical changes and which physical ? Give reason.
- a glass bottle breaking
- coal burning in air
- making a cake
- wool being knitted into a sweater
उत्तर
- Breaking of a glass bottle is a physical change because each of the broken piece of bottle is still a glass and no new substance has been formed. In the process, only the shape and size of bottle change.
- Burning of coal in air is a chemical change because the burnt coal cannot be obtained back and it is an irreversible change.
- Preparation of a cake is a chemical change as all the raw materials that go inside the mixture get cooked after baking and the process cannot be reversed.
- Knitting sweater from wool is a physical change as we can obtain back the wool from the sweater. So, it is a reversible process.
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संबंधित प्रश्न
Match the following
| Column A | Column B | ||
| (a) | Molecules | (i) | Water boils |
| (b) | 100° C | (ii) | Evaporation |
| (c) | 0° C | (iii) | Changes from solid to gas |
| (d) | At all temperatures | (iv) | Matter |
| (e) | Camphor | (v) | Water freezes |
Give one difference between atoms and molecules.
Write true or false for each statement. Rewrite the false statement correctly.
Matter cannot exist in different states.
All kinds of matter
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Bromine and air take about 15 minutes to diffuse completely but bromine diffuses into a vacuum very rapidly. Why is this so?
What is the other name for impure substances ? Give two examples of impure substances.
Which of the following statements are true for pure substances ?
- pure substances contain only one kind of particles
- pure substances may be compounds or mixtures
- pure substances have the same composition throughout
- pure substances can be exemplified by all elements other than nickel
Which of the following is not an emulsion ?
Which one of the following is not a chemical change ?
How will you separate iron pins from sand ?
How will you separate camphor, common salt and iron nails from their mixture ?
Which method is better for recovering sugar from sugar solution : evaporation or crystallisation ? Give reason
for your answer.
The liquid air has three components X, Y and Z whose boiling points are : –186°C, –183°C and –196°C,
respectively. When liquid air is fed into a tall fractional distillation column from near its bottom and warmed
up slowly :
(a) Which component will be collected from near the bottom of the fraction distillation column ? Why ?
(b) Which component will be collected from the top part of the fractional distillation column ? Why ?
(c) Which component will be collected from the middle part of the fractional distillation column ? Why ?
(d) What could the component X, Y and Z be ?
Explain the meaning of the term ‘matter’.
Stars including Sun are covered in ______.
Liquids cannot be compressed and they have fixed volume.
Evaporation does form bubbles.
Define the term matter.
