NCERT SOLUTION CLASS 9 CHAPTER 2 (IS MATTER AROUND US PURE)

NCERT SOLUTION CLASS 9 CHAPTER 2 (IS MATTER AROUND US PURE ) PAGE NO. 15

QUESTION NO. 1

What is meant by substance ?

ANSWER NO. 1

A pure substance consist of single type of particle. It is a pure single form of matter. It has definite properties and composition. Example - Iron.

QUESTION NO. 2

List the points of differences between homogeneous and heterogeneous mixtures.

ANSWER NO. 2

HOMOGENEOUS MIXTURE

Particles are uniformly distributed throughout the mixture.
It has a uniform composition.
Components cannot be separated easily.
Example - Solution of sugar and alloys.

HETEROGENEOUS MIXTURE

All the particles are completely mixed and can be distinguished with the eye or under a microscope.
It has a irregular composition.
Components can be separated easily.
Example - Mixture of sand and common salt, mixture of sand and water.

ANSWER OF PAGE NO 18

QUESTION NO. 1

Differentiate between homogeneous and heterogeneous mixtures with examples.

ANSWER NO. 1

HOMOGENEOUS MIXTURE

Particles are uniformly distributed throughout the mixture.
It has a uniform composition.
Components cannot be separated easily.
Example - Solution of sugar and alloys.

HETEROGENEOUS MIXTURE

All the particles are completely mixed and can be distinguished with the eye or under a microscope.
It has a irregular composition.
Components can be separated easily.
Example - Mixture of sand and common salt, mixture of sand and water.

QUESTION NO. 2

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

ANSWER NO. 2

A sol is a heterogeneous mixture which contain physically distinct parts and have non - uniform composition.

A solution is a homogeneous mixture of two or more substances.

A suspension is a heterogenous mixture in which the solute particles do not dissolve but remain suspended throughout the bulb of the medium.

QUESTION NO. 3

To make a saturated solution, 36g of sodium chloride is dissolved in 100g of water at 293 K. Find its concentration at this temperature.

ANSWER NO. 3

Mass of solute = 36g
Mass of solvent = 100g

Mass of solution = 100+36 = 136g
Concentration of solution = Mass of solute X 100
Mass of solution
= 36 X 100
136
= 26.47%

PAGE NO. 24

QUESTION NO. 1

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 gases,
dissolving common salt in water,
making a fruit salad with raw fruits, and
burning of paper and wood.

ANSWER NO. 1

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 water to form a stream is a physical change.
Passing of electric current, through water and water breaking down into hydrogen and oxygen gases - chemical change.
Dissolving common salt in water - physical change.
Making fruit salad with raw fruits - physical.
Burning of paper and wood - chemical change.

QUESTION NO. 2

Try segregating the things around you as pure substances or mixtures.

ANSWER NO. 2

A pure substance is made up of only one type of atoms or molecules where as mixtures are made up of combination of different types of particles.

Some of the things around us are -

Wood, air, milk, tap water, sodium chloride, gold ornament, alcohol, vinegar, diamond, steel, ice cream, naphthalene balls, baking soda, graphite, salt solution, alum, kerosene oil, steam etc. out of these
Pure substances are -
Naphthalene balls, sodium chloride, distilled water, diamond, steam, alum, alcohol, graphite, baking soda.

MIXTURE

Tap water, milk, air, gold ornament, ice cream, steel, kerosene oil, salt solution, brass, vinegar, wood.
Km

QUESTION NO. 1

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 gases,
dissolving common salt in water,
making a fruit salad with raw fruits, and
burning of paper and wood.

ANSWER NO. 1

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 water to form a stream is a physical change.
Passing of electric current, through water and water breaking down into hydrogen and oxygen gases - chemical change.
Dissolving common salt in water - physical change.
Making fruit salad with raw fruits - physical.
Burning of paper and wood - chemical change.

QUESTION NO. 2

Try segregating the things around you as pure substances or mixtures.

ANSWER NO. 2

A pure substance is made up of only one type of atoms or molecules where as mixtures are made up of combination of different types of particles.

Some of the things around us are -

ANSWER OF EXERCISES

QUESTION NO. 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 tea.

(i) Wheat grains from sand.

(j) Fine mud particles suspended in water.

ANSWER NO. 1

(a) Evaporation.
(b) Sublimation.
(c) By using a suitable filter.
(d) Chromatography.
(e) By centrifugal machine or churning the curd by hand.
(f) Decantation.
(g) Filtration.
(h) By the process of magnetic separation.
(i) By winnowing.
(j) Coagulation and decantation.
Alum is added to muddy water which makes the soil particles heavier and settle down in bottom. The clean water is then separated by decantation.

QUESTION NO. 2

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

ANSWER NO. 2

For making tea following steps are to be taken -
(i) Take 100ml of water as a solvent and boil it for few minute.
(ii) Add one tea spoon sugar, one tea spoon tea leaves and 50ml of milk as a solute.
(iii) Boil it for few minutes so that sugar will dissolve in solution as sugar is soluble in water.
(iv) Filter the solution in a cup. The insoluble tea leaves will be left behind as residue.

QUESTION NO. 3

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 substance
dissolved in 100 grams of water to form a saturated solution).

Substance Temperature in K
Dissolved 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 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 NO. 3

(a) The solubility of potassium nitrate at 313 K is 62gm. Hence 62gm of potassium nitrate is required to make a saturated solution of potassium nitrate in 100gm of water at 313 K.
So to make a saturated solution in 50gms of water the required potassium nitrate will be 62/2 = 31gm.

(b) When a saturated solution of potassium chloride at 353 K is left to cool, then the solid potassium chloride will gradually separate from the solution ( because the solubility decrease on cooling.)

(c) The solubility of different salts at 293 K is potassium nitrate 32gm, Sodium chloride 36gm, Potassium chloride 35gm and Ammonium chloride 37gm.
Ammonium chloride has the highest solubility ( 37gm) at this temperature of 293 K.

(d) According to the given data solubility of a salt increases on increasing the temperature.

QUESTION NO. 4

4.Explain the following giving examples.
(a)saturated solution
(b)pure substance
(c)colloid
(d)suspension

ANSWER NO. 4

(a) Saturated Solution : At a particular temperature, a solution that has dissolved as much solute as it is capable of dissolving, is said to be saturated solution. It is also defined as if no more solute can be dissolved in a solution at a given temperature, it is called saturated solution.

(b) Pure Substance : A pure substance consist of a particles which have same chemical nature. A pure substance consist of a single type of particles.

(c) Colloid : In colloid particles are uniformly spread throughout the solution. Because of smaller size of particles, the appears to be homogeneous. But colloidal solution is a heterogeneous mixture. Example : milk, blood.

(d) Suspension : A suspension is a heterogeneous mixture in which the solute prticles do not dissolve but remained suspended throughout the bulk of the medium. The particles of suspension are visible to the naked eyes.

QUESTION NO. 5

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

ANSWER NO. 5

HOMOGENEOUS HETEROGENEOUS
MIXTURE MIXTURE
1. Soda Water 1. Wood
2. Vinegar 2. Air
3. Filtered Tea 3. Soil

QUESTION NO. 6

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

ANSWER NO. 6

By checking the boiling temperature of the liquid it can confirmed that given water is pure or not. If it boils at 100 C it is said be pure. But if there is a decrease or increase in the boiling point, it confirms that water has added impurities.

QUESTION NO. 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.

ANSWER NO. 7

PURE SUBSTANCES

Iron
Ice
Mercury
Hydrochloric Acid
Calcium Oxide

QUESTION NO. 8

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

ANSWER NO. 8

SOLUTIONS

Sea Water
Air
Soda Water

QUESTION NO. 9

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

ANSWER NO. 9

Milk and starch solution from the above list of solution will show ˋˋ Tyndall effect ˋˋ .

QUESTION NO. 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

ANSWER NO. 10

COMPOUND MIXTURE
1. Calcium Carbonate 1. Soil
2. Carbon dioxide 2. Sugar Solution
3. Methane 3. Coal
4. Air
5. Blood
6. Soap

QUESTION NO. 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.

ANSWER NO. 11

CHEMICAL CHANGES

Growth of plants
Rusting of iron
Cooking of food
Digestion of food
Burning of a candle