Chapter 2 – Is Matter Around Us Pure
In-Text Questions and Answers
Page 15 – Questions and Answers
Question 1
What is meant by a substance?
Answer:
A substance is a form of matter that is pure and consists of only one kind of particles.
It has a fixed composition and definite properties.
Examples:
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Pure water
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Iron
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Sugar
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Oxygen
Question 2
List the points of differences between homogeneous and heterogeneous mixtures.
Answer:
| Basis | Homogeneous Mixture | Heterogeneous Mixture |
|---|---|---|
| Composition | Uniform throughout | Non-uniform |
| Appearance |
Looks the same everywhere |
Different parts are visible |
| Phases | Single phase | Two or more phases |
| Components visibility |
Components not visible separately |
Components visible separately |
| Examples | Salt solution, sugar solution, air |
Oil and water, soil, sand and iron filings |
Page 18 – Questions and Answers
Question 1
Differentiate between homogeneous and heterogeneous mixtures with examples.
Answer:
| Basis | Homogeneous Mixture | Heterogeneous Mixture |
|---|---|---|
| Composition | Uniform throughout | Non-uniform |
| Phases | Single phase | Two or more phases |
| Visibility of components | Not visible separately | Visible separately |
| Appearance | Same throughout | Different at different places |
| Examples | Salt solution, sugar solution, air | Oil and water, soil, sand in water |
Question 2
How are sol, solution and suspension different from each other?
Answer:
| Property | Solution | Colloid (Sol) | Suspension |
|---|---|---|---|
| Nature | Homogeneous | Heterogeneous (appears homogeneous) | Heterogeneous |
| Particle size | Very small (< 1 nm) | Intermediate (1–1000 nm) | Large (> 1000 nm) |
| Visibility of particles | Not visible | Not visible to naked eye | Visible |
| Tyndall effect | No | Yes | Yes |
| Stability | Stable | Stable | Unstable |
| Filtration | Cannot be separated | Cannot be separated by ordinary filtration | Can be separated |
| Examples | Salt in water | Milk, starch solution | Muddy water |
Question 3
To make a saturated solution, 36 g of sodium chloride is dissolved in 100 g of water at 293 K.
Find its concentration at this temperature.
Answer:
Given:
-
Mass of solute (NaCl) = 36 g
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Mass of solvent (water) = 100 g
Mass of solution =
Mass by Mass Percentage (% w/w)
Formula
Calculation:
Final Answer:
The concentration of the solution is 26.47% (mass by mass).
Page 19 – Questions and Answers
Question 1
Classify the following as physical or chemical changes:
Answer:
| Change | Type of Change | Reason (in one line) |
|---|---|---|
| Cutting of trees | Physical | Only size/shape changes, no new substance |
| Melting of butter in a pan | Physical |
Change of state only |
| Rusting of almirah | Chemical |
New substance (rust) is formed |
| Boiling of water to form steam | Physical |
Reversible change of state |
| Passing electric current through water and water breaking into hydrogen and oxygen | Chemical |
New substances are formed |
| Dissolving common salt in water | Physical |
No new substance, reversible |
| Making a fruit salad with raw fruits | Physical | Only mixing/cutting |
| Burning of paper and wood | Chemical |
New substances (ash, gases) formed |
Question 2
Try segregating the things around you as pure substances or mixtures.
Answer:
Pure Substances:
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Iron
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Copper
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Sugar
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Distilled water
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Oxygen
Mixtures:
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Air
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Milk
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Soil
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Sea water
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Tea
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Fruit salad
Explanation:
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Pure substances contain only one kind of particles.
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Mixtures contain two or more substances mixed together.