# Is Matter Around Us Pure NCERT Solutions

## Chapter 2

Page No. 15

Q1. What is meant by a substance?
Ans. A pure substance consists of a single type of particles.

Q2. List the points of differences between homogeneous and heterogeneous mixtures.
Ans.

 Homogeneous Mixture Heterogeneous Mixture It has a uniform composition. It doesn’t have a uniform composition. No visible boundaries of separation. Shows visible boundaries of separation. They consist of only one phase. Ex – sugar + water -> sugar solution. They consist of more than one phase. Ex – sugar + sand

Page No. 18

Q1. Differentiate between homogeneous and heterogeneous mixtures with examples.
Ans.

 Homogeneous Mixture Heterogeneous Mixture It has a uniform composition. It doesn’t have a uniform composition. No visible boundaries of separation. Shows visible boundaries of separation. They consist of only one phase. Ex – sugar + water -> sugar solution. They consist of more than one phase. Ex – sugar + sand

Q2. How are sol, solution and suspension different from each other?
Ans.

 Sol. (Colloid) Solution Suspension 1. Size of solute particles between 1nm to  100nm Size of solute particles less than 1nm. Size of solute particles more than 100nm. 2. It is stable. It is unstable. It is unstable. 3. It scatters a beam of light. It does not scatter light. It scatters a beam of light. 4. Solute particles pass through filter paper. Solute particles pass through filter paper. Solute particles do not pass through filter paper.

Q3. 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.
Ans. Mass of solute (sodium chloride) = 36 g
Mass of solvent (water) = 100 g
Mass of solution = Mass of solute + Mass of solvent
= 36 g + 100 g = 136 g
Concentration = (Mass of solute ⁄ Mass of solution) × 100
= (36 ⁄ 136)×100 = 26.47%

Page No. 24

Q1. How will you separate a mixture containing kerosene and petrol (difference in their boiling points is more than 25°C), which are miscible with each other?
Ans. A mixture of kerosene and petrol which are miscible with each other can be separated by distillation.
Method :

• Take a mixture in a distillation flask.
• Fit it with a thermometer.
• Arrange the apparatus as shown in the figure.
• Heat the mixture slowly.
• Petrol vaporises first as it has the lower boiling point. It condenses in the condenser and is collected from the condenser outlet.
• Kerosene is left behind in the distillation flask.

Q2. Name the technique to separate
(i) butter from curd,
(ii) salt from sea-water,
(iii) camphor from salt.
Ans. (i) Centrifugation,
(ii) Evaporation,
(iii) Sublimation.

Q3. What type of mixtures are separated by the technique of crystallisation?
Ans. Crystallisation technique is used to purify solid with some impurities in it. Example: Salt from sea-water.

Page No. 24

Q1. Classify the following as chemical or physical changes:

• cutting of trees,
• melting of butter in a pan,
• rusting of almirah,
• boiling of water to form steam,
• passing of electric current, through water and the water breaking down into hydrogen and oxygen gas,
• dissolving the common salt in water,
• making a fruit salad with raw fruits and
• burning of paper and wood.

Ans.

• cutting of trees is a physical change.
• melting of butter in a pan is a physical change.
• rusting of almirah is a chemical change.
• boiling of water to form steam is a physical change.
• passing of electric current through water and the water breaking down into hydrogen and oxygen gases is a chemical change.
• dissolving the common salt in water is a physical change.
• making a fruit salad with raw fruits is a physical change.
• the burning of paper and wood is a chemical change.

Q2. Try segregating the things around you as pure substances or mixtures
Ans. Pure substances—Water, bread, sugar and gold.
Mixtures—Steel, plastic, paper, talc, milk and air.

EXERCISES

Q1. 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 the water.
(g) Tea leaves from tea.
(h) Iron pins from sand.
(i) Wheat grains from the husk.
(j) Fine mud particles suspended in water.
Ans. (a) Evaporation or crystallisation
(b) Sublimation
(c) Filtration
(d) Chromatography
(e) Centrifugation
(f) Separating funnel
(g) Filtration
(h) Magnetic separation
(i) Winnowing/ sedimentation
(j) Decantation and filtration

Q2. Write the steps you would use for making tea. Use the words, solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
Ans. 1. Take a cup of water in a container as the solvent and heat it.
2. Add sugar in it which is solute. Heat it till all sugar dissolves.
3. You get a solution of water and sugar.
4. Sugar is soluble in water completely.
5. Add half a teaspoon of tea-leaves, it is insoluble in water.
6. Boil the content, add milk which is also soluble in water, boil again.
7. Filter the tea with the help of a strainer, the tea collected in a cup is filtrate and the tea leaves collected on the strainer is residue.

Q3. Pragya tested the solubility of three different substances at different temperatures and collected, the data as given below (results are given in the following table, as grams of the substance dissolved in 100 grams of water to form a saturated solution).

 Substance Dissolved Temperature in K 283 293 313 333 353 Solubility 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 coo! at room temperature. What would she observe us 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?
Ans. (a) Mass of KNO3  to produce a saturated solution of KNO3 in 100 grams of water at 313K = 62g
∴ Mass of KNO3 in 50 grams of water at 313K = (62×50) ⁄ 100 = 31.0 g
(b) Crystals of potassium chloride will be obtained by cooling the saturated solution.
(c) The solubility of each salt at 293K is

1. potassium nitrate        → 32g
2. sodium chloride          → 36g
3. potassium chloride      → 35g
4. ammonium chloride    → 37g

(d) On increasing the temperature, solubility of a salt increases.

Q4. Explain the following giving examples:
(a) Saturated solution
(b) Pure substance
(c) Colloid
(d) Suspension
Ans. (a) Saturated solution: In a given solvent when no more solute can dissolve further at a given temperature is called a saturated solution.
(b) Pure substance: A pure substance consists of a single type of particles. E.g., gold, silver.
(c) Colloid: A colloid is a solution in which the size of solute particles are bigger than that of true solution. These particles cannot be seen with our naked eyes, they are stable, e.g., ink, blood.
(d) Suspension: It is a heterogeneous mixture in which the solute particles are big enough to settle down, e.g., chalk-water, paints, etc.

Q5. Classify each of the following as a homogeneous or heterogeneous mixture: soda water, wood, air. soil, vinegar, filtered tea.
Ans. Homogeneous: Soda water, vinegar, filtered tea.
Heterogeneous: Wood, air, soil.

Q6. How would, you confirm that a colourless liquid given to you is pure water?
Ans. By finding the boiling point of a given colourless liquid. If the liquid boils at 100°C at atmospheric pressure, then it is pure water. This is because pure substances have fixed melting and boiling point.

Q7. Which of the following materials fall under the category of a “pure substance”?
(a) Ice (b) Milk (c) Iron
(d) Hydrochloric acid (e) Calcium oxide (f) Mercury
(g) Back (h) Wood (i) Air.
Ans. Pure substances are ice, iron, hydrochloric acid, calcium oxide and mercury.

Q8. Identify the solutions among the following mixtures.
(a) Soil (b) Seawater
(c) Air (d) Coal
(e) Soda water.
Ans. Solutions are seawater soda water and air.

Q9. Which of the following will show “Tyndall effect”?
(a) Salt solution (b) Milk
(c) Copper sulphate solution (d) Starch solution.
Ans. Milk and starch solution.

Q10. 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
Ans. Elements – Compounds – Mixtures
Sodium – Calcium carbonate – Sugar solution
Silver – Methane – Soil
Tin – Carbon dioxide – Coal
Silicon – Soap – Air, Blood

Q11. Which of the following are chemical changes?
(a) The 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.
Ans. Chemical changes are:
(a) Growth of a plant (b) Rusting of iron
(c) Cooking of food (d) Digestion of food
(e) Burning of a candle

For more resources
NCERT Solutions for Class 9 Science

NCERT Solutions for Class 9