Multiple Choice Questions
1. Which of the following statements are true for pure substances?
Correct Answer:
(b) → (i) and (iii)
- (i)
True – Pure substances contain only one kind of particle. - (ii)
False – Pure substances cannot be mixtures. - (iii) True – They have the same composition throughout.
- (iv) False – All elements, not just those excluding nickel, can be pure substances.
2. Rusting of an article made up of iron is called
Correct Answer:
(c) corrosion and it is a chemical change
- Rusting is a type of corrosion.
- It is a chemical change as new substances (like iron oxide) are formed.
3. A mixture of sulphur and carbon disulphide is
Correct Answer:
(d) homogeneous and does not show Tyndall effect
- Sulphur dissolves completely in carbon disulphide.
- It forms a true solution, which is homogeneous.
- True solutions do not show the Tyndall effect.
4. Tincture of iodine has antiseptic properties. This solution is made by dissolving
Correct Answer:
(d) iodine in alcohol
- Tincture of iodine = Iodine + Alcohol
- It is used as an antiseptic.
- Sometimes sold as Betadine.
5. Which of the following are homogeneous in nature?
(i) ice
(ii) wood
(iii) soil
(iv) air
Correct Answer:
(c) → (i) and (iv)
- (i) Ice – Pure solid water (homogeneous if pure).
- (ii) Wood – Heterogeneous (fibers, vessels, moisture, etc.)
- (iii) Soil – Heterogeneous (particles of different sizes/composition)
- (iv) Air – Homogeneous mixture of gases (when clean)
6. Which of the following are physical changes?
(i) Melting of iron metal – 
Physical change (only change in state)
(ii) Rusting of iron – 
Chemical change
(iii) Bending of an iron rod – Physical change (no new substance)
(iv) Drawing a wire of iron metal – Physical change (just shape change)
Correct Answer:
(c) → (i), (iiii) and (iv)
7. Which of the following are chemical changes?
(i) Decaying of wood – Chemical change (decomposition)
(ii) Burning of wood – Chemical change (combustion produces new substances)
(iii) Sawing of wood – Physical change (only shape changes)
(iv) Hammering a nail into wood – Physical change
Correct Answer:
(a) → (i) and (ii)
8. Two substances, A and B were made to react to form a third substance, A_2B, according to the following reaction:
Which of the following statements concerning this reaction are incorrect?
(i) The product A_2B shows the properties of substances A and B
(ii) The product will always have a fixed composition
(iii) The product so formed cannot be classified as a compound
(iv) The product so formed is an element
Let’s analyze each:
- (i) Incorrect – Product does NOT show properties of A and B (compound formed).
- (ii) Correct – Compounds have a fixed composition.
- (iii) Incorrect – Product is a compound, so this statement is wrong.
- (iv) Incorrect – Product A₂B is a compound, not an element.
Incorrect statements: (i), (iii), and (iv)
Correct Answer:
(c) → (i), (iii) and (iv)
9. Two chemical species X and Y combine together to form a product P which contains both X and Y.
X and Y cannot be broken down into simpler substances by simple chemical reactions. Which of the following concerning the species X, Y and P are correct?
(i) P is a compound
(ii) X and Y are compounds
(iii) X and Y are elements
(iv) P has a fixed composition
(i) P is a compound – Yes
(ii) X and Y are compounds – Incorrect (They are elements)
(iii) X and Y are elements – Correct
(iv) P has a fixed composition – Correct
Correct Answer:
(d) → (i), (iii) and (iv)
Short Answer Questions
10. Suggest separation techniques for the mixtures:
(a) Mercury and water – Use a separating funnel (immiscible liquids)
(b) Potassium chloride and ammonium chloride – Use sublimation (NH₄Cl sublimates)
(c) Common salt, water, and sand
- Filtration to remove sand
- Evaporation to remove water and get salt
(d) Kerosene oil, water and salt
- Separating funnel (kerosene and water)
- Evaporation to get salt from water
11. Which tube (a or b) will be more effective as a condenser?
Answer:
Tube (a) is more effective. It has a larger surface area (due to packed beads) which helps in faster condensation.
12. Salt recovery techniques:
Besides evaporation, you can also use crystallization to recover pure salt from a solution. Crystallization gives larger and purer crystals.
13. Is sea-water homogeneous or heterogeneous?
Sea water is:
- Homogeneous: when dissolved salts and water form a uniform solution.
- Heterogeneous: if it contains floating impurities, sand, or marine life.
Conclusion: It can behave as both, depending on what it contains.
14. How to recover acetone from salt solution?
Since acetone boils at 56°C, use simple distillation.
Justification: Acetone has a lower boiling point than water, so it will evaporate first and can be condensed.
15. What would you observe when:
(a) Saturated KCl solution cooled – Crystals of KCl will form (excess salt precipitates).
(b) Sugar solution heated to dryness – Water evaporates; you are left with solid sugar (can char if overheated).
(c) Iron filings and sulphur strongly heated – A chemical reaction occurs; forms iron sulphide (FeS), a compound.
16. Why colloids don’t settle but suspensions do?
- Colloid particles are small and constantly moving (Brownian motion).
- Suspensions have larger, heavier particles that settle due to gravity when left undisturbed.
17. Difference between smoke and fog:
| Smoke | Fog |
|---|---|
| Solid particles in gas | Liquid droplets in gas |
| Formed by combustion | Formed by condensation |
| Example of aerosol | Also an aerosol |
18. Classify physical or chemical properties:
(a) Steel composition – Physical property (no new substance formed)
(b) Zinc + HCl → hydrogen – Chemical property (gas evolves, new substance)
(c) Sodium soft to cut – Physical property
(d) Metal oxides form alkalis with water – Chemical property
19.
Correct student: C
A 50% (mass/volume) solution means:
So we need:
20. Name the process:
(a) Dry ice is kept at room temperature and at one atmospheric pressure → Sublimation
Explanation:
- Dry ice is solid carbon dioxide (CO₂).
- At room temperature and 1 atmospheric pressure, dry ice does not melt into liquid.
- Instead, it directly changes from solid to gas without becoming liquid in between.
- This direct change from solid to gas is called sublimation.
(b) Drop of ink spreading → Diffusion
(c) KMnO₄ crystal stirred in water → Dissolution/Diffusion
(d) Acetone bottle left open → Evaporation, Diffusion
(e) Milk churning → Centrifugation
(f) Sand settling down → Sedimentation
(g) Light scattering in dust → Tyndall effect
21.
- Sample B has impurities (boils at 102°C), so it will not freeze at 0°C.
- Sample A is pure water (boils at 100°C), so it will freeze at 0°C.
22.
Favourable qualities of gold when alloyed:
- Hardness (for strength)
- Malleability and lustre remain
- Better for jewellery making
23.
- Sonorous and highly ductile → Metal
- Other expected properties: Malleable, good conductor of heat and electricity, lustrous
24. Examples and methods
(a) Volatile + non-volatile → Ink + water, use evaporation or distillation
(b) Two volatile (diff boiling points) → Alcohol + water, use fractional distillation
(c) Two immiscible liquids → Oil + water, use separating funnel
(d) Sublimation → Ammonium chloride + salt, use sublimation
(e) Colored soluble components → Ink, use chromatography
25. Fill in the blanks
(a) A colloid is a heterogeneous mixture, separated by centrifugation
(b) Ice, water, vapour → Look different, but chemically the same
(c) Chloroform and water:
- Upper layer = Water
- Lower layer = Chloroform (denser)
(d) Mixture of miscible liquids (boiling point diff < 25K) → Fractional distillation
(e) When light is passed through water containing a few drops of milk →
- The light shows a bluish tinge.
- This is due to the scattering of light by milk particles.
- The phenomenon is called the Tyndall effect.
- This indicates that milk is a colloid.
26.
Sucrose crystals from sugarcane and beetroot:
- It is a pure substance, because sucrose is a single compound (C₁₂H₂₂O₁₁).
- Even though sources are different, chemically it’s the same.
27.
Examples of Tyndall effect:
- Sunlight passing through a forest or fog
- Torchlight in a dusty room
- Headlights of a vehicle in mist
- Laser beam through smoke in a dark room
28.
Can alcohol be separated from water using a separating funnel?
No, because alcohol and water are miscible (they mix completely).
Instead, use fractional distillation (they have different boiling points).
29.
On heating calcium carbonate → calcium oxide + carbon dioxide
(a) This is a chemical change (new substances formed).
(b)
- Yes, you can prepare:
- One basic solution: calcium oxide + water → calcium hydroxide
- One acidic solution: dissolve CO₂ in water → carbonic acid
30.
(a) Lustrous non-metal: Iodine
(b) Liquid non-metal at room temp: Bromine
(c) Allotropic form of a non-metal that’s a good conductor: Graphite
(d) Non-metal forming most compounds: Carbon
(e) Non-carbon non-metal with allotropy: Sulphur
(f) Non-metal needed for combustion: Oxygen
31.
Classify into Elements and Compounds:
Elements:
- Cu (Copper)
- Zn (Zinc)
- O₂ (Oxygen)
- F₂ (Fluorine)
- Hg (Mercury)
- Diamond (Carbon in crystalline form)
Compounds:
- H₂O (Water)
- NaCl (aq) (Salt solution)
- CaCO₃ (Calcium carbonate)
Mixtures (not pure elements or compounds):
- Sand
- Wood
32. Which of the following are not compounds?
Not compounds (i.e., elements):
- (a) Chlorine gas
- (c) Iron
- (e) Aluminium
- (f) Iodine
- (g) Carbon
- (i) Sulphur powder
Compounds (rest):
- (b) Potassium chloride
- (d) Iron sulphide
- (h) Carbon monoxide
Long Answer Questions