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Is Matter Around Us Pure
Physics IX : Complete NCERT Exercise Solutions
"Get NCERT Solutions for Class 9 Science Chapter 2 Is Matter Around Us Pure. Understand mixtures, solutions, suspensions, colloids, separation techniques, and purity of substances with exam-oriented explanations.
Question 2.1
Which separation techniques will you apply for the separation of the following?
(a) Sodium chloride from its solution in water.
(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.
(c) Small pieces of metal in the engine oil of a car.
(d) Different pigments from an extract of flower petals.
(e) Butter from curd.
(f) Oil from water.
(g) Tea leaves from tea.
(h) Iron pins from sand.
(i) Wheat grains from husk.
(j) Fine mud particles suspended in water.
(a) Sodium chloride from its solution in water.
(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride.
(c) Small pieces of metal in the engine oil of a car.
(d) Different pigments from an extract of flower petals.
(e) Butter from curd.
(f) Oil from water.
(g) Tea leaves from tea.
(h) Iron pins from sand.
(i) Wheat grains from husk.
(j) Fine mud particles suspended in water.
Answer & Explanation:
(a) Evaporation
(b) Sublimation
(c) Filtration or Decantation
(d) Chromatography
(e) Centrifugation
(f) Separating Funnel
(g) Filtration
(h) Magnetic Separation
(i) Winnowing or Sieving
(j) Filtration or Sedimentation & Decantation
(b) Sublimation
(c) Filtration or Decantation
(d) Chromatography
(e) Centrifugation
(f) Separating Funnel
(g) Filtration
(h) Magnetic Separation
(i) Winnowing or Sieving
(j) Filtration or Sedimentation & Decantation
Question 2.2
Write the steps you would use for making tea. Use the words: solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
Answer & Explanation:
1. Boil water (solvent).
2. Add tea leaves and sugar. Sugar is soluble and dissolves completely.
3. Tea leaves are insoluble and form a mixture.
4. After boiling, filter the mixture. The liquid collected is the filtrate, and the tea leaves left behind are the residue.
5. The solute (sugar and tea essence) is now in the solvent (water), forming a solution of tea.
2. Add tea leaves and sugar. Sugar is soluble and dissolves completely.
3. Tea leaves are insoluble and form a mixture.
4. After boiling, filter the mixture. The liquid collected is the filtrate, and the tea leaves left behind are the residue.
5. The solute (sugar and tea essence) is now in the solvent (water), forming a solution of tea.
Question 2.3
Pragya tested the solubility of three different substances at different temperatures and collected the data as given below (results are given in grams of substance dissolved in 100 grams of water to form a saturated solution).
(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K?
(b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperature. What would she observe as the solution cools? Explain.
(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?
(d) What is the effect of change of temperature on the solubility of a salt?
| Substance Dissolved | 283 K | 293 K | 313 K | 333 K | 353 K |
|---|---|---|---|---|---|
| Potassium nitrate | 21 | 32 | 62 | 106 | 167 |
| Sodium chloride | 36 | 36 | 36 | 37 | 37 |
| Potassium chloride | 35 | 35 | 40 | 46 | 54 |
| Ammonium chloride | 24 | 37 | 41 | 55 | 66 |
(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313 K?
(b) Pragya makes a saturated solution of potassium chloride in water at 353 K and leaves the solution to cool at room temperature. What would she observe as the solution cools? Explain.
(c) Find the solubility of each salt at 293 K. Which salt has the highest solubility at this temperature?
(d) What is the effect of change of temperature on the solubility of a salt?
Answer & Explanation:
(a) At 313 K, solubility of KNO₃ = 62 g per 100 g water.
For 50 g water: \( \frac{62}{2} = 31 \, \text{g} \).
(b) Crystals of KCl will form because solubility decreases on cooling, making the solution supersaturated.
(c) At 293 K:
KNO₃: 32 g
NaCl: 36 g
KCl: 35 g
NH₄Cl: 37 g
Highest: Ammonium chloride (37 g)
(d) Solubility generally increases with temperature for most salts (like KNO₃, KCl, NH₄Cl), but for some (like NaCl), it changes very little.
For 50 g water: \( \frac{62}{2} = 31 \, \text{g} \).
(b) Crystals of KCl will form because solubility decreases on cooling, making the solution supersaturated.
(c) At 293 K:
KNO₃: 32 g
NaCl: 36 g
KCl: 35 g
NH₄Cl: 37 g
Highest: Ammonium chloride (37 g)
(d) Solubility generally increases with temperature for most salts (like KNO₃, KCl, NH₄Cl), but for some (like NaCl), it changes very little.
Question 2.4
Explain the following giving examples.
(a) saturated solution
(b) pure substance
(c) colloid
(d) suspension
(a) saturated solution
(b) pure substance
(c) colloid
(d) suspension
Answer & Explanation:
(a) Saturated solution: A solution in which no more solute can be dissolved at a given temperature. Example: Sugar solution with undissolved sugar at the bottom.
(b) Pure substance: A substance made up of only one kind of particles, with fixed composition and properties. Example: Distilled water, gold.
(c) Colloid: A heterogeneous mixture where particles are too small to be seen but large enough to scatter light (Tyndall effect). Example: Milk, fog.
(d) Suspension: A heterogeneous mixture where particles are visible, settle down, and can be separated by filtration. Example: Muddy water.
(b) Pure substance: A substance made up of only one kind of particles, with fixed composition and properties. Example: Distilled water, gold.
(c) Colloid: A heterogeneous mixture where particles are too small to be seen but large enough to scatter light (Tyndall effect). Example: Milk, fog.
(d) Suspension: A heterogeneous mixture where particles are visible, settle down, and can be separated by filtration. Example: Muddy water.
Question 2.5
Classify each of the following as a homogeneous or heterogeneous mixture.
soda water, wood, air, soil, vinegar, filtered tea.
soda water, wood, air, soil, vinegar, filtered tea.
Answer & Explanation:
Homogeneous: Soda water, air, vinegar, filtered tea.
Heterogeneous: Wood, soil.
Heterogeneous: Wood, soil.
Question 2.6
How would you confirm that a colourless liquid given to you is pure water?
Answer & Explanation:
1. Check boiling point: Pure water boils at 373 K (100°C) at 1 atm.
2. Check freezing point: Pure water freezes at 273 K (0°C).
3. Test with anhydrous copper sulphate: Turns blue if water is present.
4. Evaporation: Leaves no residue if pure.
2. Check freezing point: Pure water freezes at 273 K (0°C).
3. Test with anhydrous copper sulphate: Turns blue if water is present.
4. Evaporation: Leaves no residue if pure.
Question 2.7
Which of the following materials fall in the category of a “pure substance”?
(a) Ice
(b) Milk
(c) Iron
(d) Hydrochloric acid
(e) Calcium oxide
(f) Mercury
(g) Brick
(h) Wood
(i) Air
(a) Ice
(b) Milk
(c) Iron
(d) Hydrochloric acid
(e) Calcium oxide
(f) Mercury
(g) Brick
(h) Wood
(i) Air
Answer & Explanation:
Pure substances: Ice, Iron, Hydrochloric acid, Calcium oxide, Mercury.
Mixtures: Milk, Brick, Wood, Air.
Mixtures: Milk, Brick, Wood, Air.
Question 2.8
Identify the solutions among the following mixtures.
(a) Soil
(b) Sea water
(c) Air
(d) Coal
(e) Soda water
(a) Soil
(b) Sea water
(c) Air
(d) Coal
(e) Soda water
Answer & Explanation:
Solutions: Sea water, Air, Soda water.
Not solutions: Soil (suspension), Coal (heterogeneous mixture).
Not solutions: Soil (suspension), Coal (heterogeneous mixture).
Question 2.9
Which of the following will show “Tyndall effect”?
(a) Salt solution
(b) Milk
(c) Copper sulphate solution
(d) Starch solution
(a) Salt solution
(b) Milk
(c) Copper sulphate solution
(d) Starch solution
Answer & Explanation:
Show Tyndall effect: Milk, Starch solution (both are colloids).
Do not show: Salt solution, Copper sulphate solution (true solutions).
Do not show: Salt solution, Copper sulphate solution (true solutions).
Question 2.10
Classify the following into elements, compounds and mixtures.
(a) Sodium
(b) Soil
(c) Sugar solution
(d) Silver
(e) Calcium carbonate
(f) Tin
(g) Silicon
(h) Coal
(i) Air
(j) Soap
(k) Methane
(l) Carbon dioxide
(m) Blood
(a) Sodium
(b) Soil
(c) Sugar solution
(d) Silver
(e) Calcium carbonate
(f) Tin
(g) Silicon
(h) Coal
(i) Air
(j) Soap
(k) Methane
(l) Carbon dioxide
(m) Blood
Answer & Explanation:
Elements: Sodium, Silver, Tin, Silicon
Compounds: Calcium carbonate, Methane, Carbon dioxide
Mixtures: Soil, Sugar solution, Coal, Air, Soap, Blood
Compounds: Calcium carbonate, Methane, Carbon dioxide
Mixtures: Soil, Sugar solution, Coal, Air, Soap, Blood
Question 2.11
Which of the following are chemical changes?
(a) Growth of a plant
(b) Rusting of iron
(c) Mixing of iron filings and sand
(d) Cooking of food
(e) Digestion of food
(f) Freezing of water
(g) Burning of a candle
(a) Growth of a plant
(b) Rusting of iron
(c) Mixing of iron filings and sand
(d) Cooking of food
(e) Digestion of food
(f) Freezing of water
(g) Burning of a candle
Answer & Explanation:
Chemical changes: Growth of a plant, Rusting of iron, Cooking of food, Digestion of food, Burning of a candle.
Physical changes: Mixing of iron filings and sand, Freezing of water.
Physical changes: Mixing of iron filings and sand, Freezing of water.
📘 Exam Preparation Tip:
Clearly differentiate between elements, compounds, and mixtures. Memorize the definitions and examples of solutions, suspensions, and colloids. Be thorough with separation techniques like centrifugation, distillation, and chromatography.