NCERT Solutions Class 9 Science Chapter 2 Is Matter Around Us Pure

1. Which separation techniques will you apply for the separation of the following?

(a) Sodium chloride from water solution: Evaporation
(b) Ammonium chloride from mixture: Sublimation
(c) Metal pieces from engine oil: Filtration
(d) Pigments from flower petals: Chromatography
(e) Butter from curd: Centrifugation
(f) Oil from water: Separating Funnel
(g) Tea leaves from tea: Filtration
(h) Iron pins from sand: Magnetic Separation
(i) Wheat grains from husk: Winnowing
(j) Fine mud particles suspended in water: Centrifugation (or Loading followed by filtration)

2. Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.

1. Take water as a solvent in a vessel and boil it.
2. Add tea powder (which is insoluble in water) and sugar (which is a solute).
3. Sugar will dissolve in water to form a solution.
4. Add milk (another solute which is soluble) to the boiling solution.
5. After boiling, filter the mixture. The tea leaves remain on the strainer as residue.
6. The tea collected in the cup is the filtrate.

3. Pragya tested the solubility of three different substances at different temperatures and collected the data…
(a) Mass of Potassium nitrate needed for saturated solution in 50g water at 313 K?
(b) Observation when saturated Potassium chloride solution at 353 K cools?
(c) Solubility at 293 K and salt with highest solubility?
(d) Effect of temperature change on solubility?

(a) At 313 K: Solubility of Potassium nitrate is 62g in 100g water.
For 50g water: $\frac{62}{100} \times 50 =$ $31 \text{ g}$.

(b) As the solution cools from 353 K to room temperature, the solubility decreases. Pragya would observe crystals of Potassium chloride separating out from the solution (crystallization).

(c) At 293 K:
Potassium nitrate: 32g
Sodium chloride: 36g
Potassium chloride: 35g
Ammonium chloride: 37g
Highest Solubility: Ammonium chloride (37g).

(d) Effect: The solubility of a salt generally increases with an increase in temperature and decreases with a decrease in temperature.

4. Explain the following giving examples.
(a) Saturated solution (b) Pure substance (c) Colloid (d) Suspension

(a) Saturated Solution: A solution in which no more solute can be dissolved at a given temperature.
Example: Adding salt to water until it stops dissolving.

(b) Pure Substance: A substance consisting of a single type of particles (atoms or molecules) with fixed chemical properties.
Example: Iron, Water, 24-carat Gold.

(c) Colloid: A heterogeneous mixture where particle size is intermediate between true solution and suspension. Particles scatter light (Tyndall effect).
Example: Milk, Fog.

(d) Suspension: A heterogeneous mixture containing solid particles large enough for sedimentation.
Example: Muddy water, Chalk powder in water.

5. Classify each of the following as a homogeneous or heterogeneous mixture:
soda water, wood, air, soil, vinegar, filtered tea.

Homogeneous Mixtures: Soda water, Vinegar, Filtered tea, Air.

Heterogeneous Mixtures: Wood, Soil.

6. How would you confirm that a colourless liquid given to you is pure water?

By checking its Boiling Point. Pure water boils exactly at $100^\circ \text{C}$ (373 K) at atmospheric pressure. If the liquid boils at this exact temperature without fluctuation, it is pure water. Any impurity will elevate the boiling point.

7. Which of the following materials fall in the category of a “pure substance”?

Pure Substances:
• Ice (Compound $H_2O$)
• Iron (Element $Fe$)
• Hydrochloric acid (Compound $HCl$)
• Calcium oxide (Compound $CaO$)
• Mercury (Element $Hg$)

8. Identify the solutions among the following mixtures:
(a) Soil (b) Sea water (c) Air (d) Coal (e) Soda water

Solutions (Homogeneous Mixtures):
• (b) Sea water
• (c) Air
• (e) Soda water

[Image of Tyndall effect in a colloid] 9. Which of the following will show “Tyndall effect”?
(a) Salt solution (b) Milk (c) Copper sulphate solution (d) Starch solution

The Tyndall effect is shown by Colloids.
Correct Answers:
• (b) Milk
• (d) Starch solution

10. Classify the following into elements, compounds and mixtures.

Elements	Compounds	Mixtures
Sodium	Calcium carbonate	Soil
Silver	Methane	Sugar solution
Tin	Carbon dioxide	Coal
Silicon	Soap	Air
		Blood

11. Which of the following are chemical changes?

Chemical Changes:
• (a) Growth of a plant
• (b) Rusting of iron
• (d) Cooking of food
• (e) Digestion of food
• (g) Burning of a candle

Group Activity: Water Filtration Plant

Design:
1. Take an earthen pot with a small hole at the bottom.
2. Layer the bottom with large pebbles, followed by smaller gravel, and then fine sand on top.
3. Pour muddy water into the pot.
4. The layers act as a natural filter, trapping suspended impurities. Clean water drips out from the bottom.

Is Matter Around Us Pure?