Exploration - Science solution
Class 9 - Chapter 5: Exploring Mixtures and their Separation
Exercise Solution
1. Which of the following mixtures are correctly classified as homogeneous (Hm) and heterogeneous (Ht)?
Answer: (iv)
- Muddy water — Ht ✓
- Milk — Ht ✓ (Colloid)
- Blood — Ht ✓
- Brass — Hm ✓ (Alloy)
Therefore, Option (iv) is correct.
2. Which among the following mixtures show the Tyndall Effect?
The Tyndall effect is shown by colloidal mixtures because colloidal particles scatter light.
- (a) Air and dust particles → Yes ✓
- (b) Copper sulphate and water → No ✗ (True solution)
- (c) Starch and water → Yes ✓ (Colloid)
- (d) Acetone and water → No ✗ (True solution)
Correct Option: (iii) a and c
3. Complete Table 5.2
| Solution | Suspension | Colloid |
|---|---|---|
| Properties | Properties | Properties |
| Small-sized particles (less than 1 nm diameter) | Large-sized particles (more than 1000 nm diameter) | Moderate-sized particles (1–1000 nm) |
| Transparent | Settles down when left undisturbed | Particles remain evenly distributed |
| Cannot be separated by filtration | Separates by filtration | Scatters light |
| Does not settle down | Heterogeneous mixture | Does not settle down |
| Examples | Examples | Examples |
| Salt solution | Sand in water | Milk |
| Brass | Mud | Smoke |
| Copper sulphate solution | Muddy water | Butter |
4. Solve the following problems
(i) Concentration of ingredients in the cake recipe
Total mass of mixture = 420 g + 75 g + 5 g = 500 g
Sugar:
Concentration = (Mass of sugar / Total mass) × 100
= (75 / 500) × 100
= 15%
All-purpose flour:
Concentration = (420 / 500) × 100
= 84%
Sodium hydrogen carbonate:
Concentration = (5 / 500) × 100
= 1%
Answer: Sugar = 15%, Flour = 84%, Sodium hydrogen carbonate = 1%
(ii) Copper and zinc in brass
Brass contains 70% copper.
Mass of brass = 120 g
Copper = (70/100) × 120
= 84 g
Zinc = 120 − 84
= 36 g
Answer: Copper = 84 g, Zinc = 36 g
5. Coconut oil and water
Yes, coconut oil and water form separate layers because they are immiscible liquids.
Since coconut oil is less dense than water, it forms the upper layer.
Water forms the lower layer.
They can be separated using a separating funnel.
Apparatus Used:
- Separating funnel
- Stand and clamp
- Beaker
6. Assertion and Reason
Assertion (A): Solutions do not exhibit Tyndall effect.
Reason (R): The particles in solutions are larger than 100 nm, so they cannot scatter light.
Assertion is true because solution particles are very small and do not scatter light.
Reason is false because particles in a solution are actually less than 1 nm in size.
Correct Option: (iii) A is true, but R is false.
7. Separation of mixtures (Table 5.3)
| Mixture | Method of Separation | Reason |
|---|---|---|
| Mud from muddy water | Filtration | Mud particles are insoluble and large. |
| Plasma from blood sample | Centrifugation | Components differ in density. |
| Naphthalene and sand | Sublimation | Naphthalene sublimes while sand does not. |
| Chalk powder and common salt | Dissolve salt in water → Filter → Evaporate | Salt is soluble, chalk is insoluble. |
| Common salt and water | Evaporation / Crystallisation | Water evaporates leaving salt behind. |
| Oil from water | Separating funnel | Oil and water are immiscible liquids. |
| Pigments of flower | Chromatography | Different pigments move at different speeds. |
8. Separation of two miscible liquids
Boiling point of A = 60°C
Boiling point of B = 90°C
Since the boiling points differ by 30°C, the liquids can be separated by simple distillation.
The liquid with lower boiling point (A) vaporises first and is collected separately.
9. Evaporation, Crystallisation and Distillation
| Method | Use |
|---|---|
| Evaporation | Obtaining dissolved solid from a solution. |
| Crystallisation | Obtaining pure crystals of a solid. |
| Distillation | Separating solvent from solution or two miscible liquids. |
Crystallisation is preferred when pure crystals are required because evaporation may leave impurities behind.
10. Blood as a colloid
(i) If blood behaved like a true suspension
The particles would settle down on standing. Blood would separate into layers and could not perform its functions properly.
(ii) Dispersed phase and dispersion medium
Dispersed phase: Blood cells
Dispersion medium: Plasma
11. Separation of sand, common salt and naphthalene
Correct sequence:
- Sublimation → Separate naphthalene.
- Add water to the remaining mixture.
- Filtration → Separate sand.
- Evaporation / Crystallisation → Obtain common salt.
12. Why is distillation effective for separating water and acetone?
Water and acetone are miscible liquids.
Their boiling points are different:
- Acetone = 56°C
- Water = 100°C
Acetone boils first and can be condensed separately, making distillation an effective method.
13. Solubility Table Questions
(i) Mass of potassium nitrate required
At 40°C, solubility of KNO3 = 62 g per 100 g water
For 50 g water:
= (62 × 50) / 100
= 31 g
Answer: 31 g
(ii) Observation with ammonium chloride solution
At 80°C, solubility = 66 g per 100 g water.
At 25°C, solubility decreases considerably.
Excess ammonium chloride crystallises out on cooling.
(iii) Effect of temperature on solubility
The solubility of all four salts increases with temperature.
- Potassium nitrate shows the maximum increase.
- Ammonium chloride shows considerable increase.
- Potassium chloride shows moderate increase.
- Sodium chloride shows very little increase.
14. Sugar solutions
(i) Percentage concentration (% m/m)
% m/m = (Mass of solute / Mass of solution) × 100
Student A
= (20 / 100) × 100
= 20%
Student B
= (20 / 120) × 100
= 16.67%
Student C
= (30 / 110) × 100
= 27.27%
(ii) Most concentrated solution
Student C's solution has the highest concentration (27.27%).
Answer: Student C has the most concentrated solution.
15. Fig. 5.26
(i) Technique marked as S
Simple Distillation
(ii) Labels
- A – Distillation Flask
- B – Condenser
- C – Receiver (Conical Flask)
(iii) Mixtures separated by this technique
Simple distillation is used when boiling points differ considerably.
| Mixture | Can be separated? |
|---|---|
| Water – Acetone | Yes ✓ |
| Water – Salt | Yes ✓ |
| Acetone – Alcohol | No ✗ (Fractional distillation) |
| Sand – Salt | No ✗ |
| Alcohol – Chloroform | Yes ✓ |
| Alcohol – Benzene | No ✗ (Fractional distillation) |