9th

TEXTUAL EXERCISE – 2.1 PAGE – 15

Q.1- What is meant by a pure substance?

Ans- A substance consist of a single type of particles is called a pure substance. These particles are same in their chemical nature.

Q.2- List the point of differences between homogeneous and heterogeneous mixture.

Ans-

Homogeneous mixture	Heterogeneous mixture
(i) It has a uniform composition throughout.	(i) It does not have a uniform composition throughout.
(ii) It does not show visible boundaries of separation.	(ii) It shows visible boundaries of separation.
(iii) It has the same properties throughout the bulk.	(iii) It does not have the same properties throughout the bulk.

TEXTUAL EXERCISE- 2.2 PAGE – 18

Q.1- Differentiate between homogeneous and heterogeneous mixture with examples.

Homogeneous mixture	Heterogeneous mixture
(i) It has a uniform composition throughout.	(i) It does not have a uniform composition throughout.
(ii) It does not show visible boundaries of separation.	(ii) It shows visible boundaries of separation.
(iii) It has the same properties throughout the bulk.	(iii) It does not have the same properties throughout the bulk.
(iv) Examples- Sodium Chloride dissolved in water. Ethyl alcohol dissolved in water.	(iv) Examples- Oil and water. Sand and water.

Q.2- How are Sol, solution and suspension different from each other.

S.No.	Property	Sol (colloidal solution)	Solution	Suspension
1.	Nature	Heterogeneous	Homogeneous	Heterogeneous
2.	Particle size	1 to 100 nm	Less than 1 nm	More than 100 nm
3.	Diffusion	Diffuse slowly	Diffuse rapidly	Don’t diffuse
4.	Filtrability	Particles can pass through ordinary filter paper but not through semipermeable membrane.	Particles can pass through ordinary filter paper as well as through semipermeable membrane.	Particles can’t pass through ordinary filter paper as well as through semipermeable membrane.
5.	Appearance	Generally Clear and transparent.	Clear and transparent.	Opaque.
6.	Tyndall Effect	Show	Don’t show.	May or May not show.
7.	Visibility	Particles can be seen only with ultramicroscope.	Particles are not visible.	Particles can be seen with naked eyes or microscope.

Q.3- 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 Sodium Chloride( solute) = 36 g

Mass of water(solvent) = 100 g

Total Mass of solution ( sodium chloride +water) = 100 + 36 = 136 g

Concentration = Mass of solute/Mass of solution x 100

Concentration = 36/136 x 100 = 26.47%

Hence, the concentration of the solution is 26.47%

TEXTUAL EXERCISE- 2.3 PAGE – 24

Q.1- How will you separate a mixture containing kerosene and petrol ( difference in their boiling point is more than 25°C), which are miscible with each other.

Ans- A mixture of kerosene and petrol can be separated by simple distillation.

Method-

(i) Take the mixture in a distillation flask.

(ii) Fit it with a thermometer.

(iii) Arrange the apparatus as shown in the above figure.

(iv) Heat the mixture slowly.

(v) The boiling point of petrol is less as compare to kerosene, so it will first vapourise, condenses in the water condenser and can be collected from condenser outlet.

(vi) Kerosene is left behind in the flask.

Q.2- Name the technique to separate :

(a) Butter from curd

(b) Salt from sea water

(c) Camphor from salt

Ans- (a) Centrifugation

(b) Evaporation

(c) Sublimation

Q.3- What type of mixtures are separated by the technique of crystallization?

Ans- Crystallization method is used to separate soluble impurities. Salt from sea water and alum from impure sample can be separated by crystallization method.

TEXTUAL EXERCISE- 2.4 PAGE – 24

Q.1- Classify the following as physical change or chemical change.

(a) Cutting of trees

(b) Melting of butter in a pan

(c) Rusting of almirah

(d) Boiling of water to form steam

(e) Passing of electric current through water and the water breaking down into hydrogen and oxygen gases

(f) Dissolving common salt in water

(g) Making a fruit salad with raw fruits

(h) Burning of paper and wood

Physical change	Chemical change
Cutting of trees	Rusting of almirah
Melting of butter in a pan	Passing of electric current through water and the water breaking down into hydrogen and oxygen gases
Boiling of water to form steam	Burning of paper and wood
Dissolving common salt in water
Making a fruit salad with raw fruits

Q.2- Try segregating the things around you as pure substances and mixtures.

Ans- Pure substances – Water, gold, salt, iron, sugar.

Mixtures – Air, soil, paper, curd, wood.

TEXTUAL EXERCISE PAGE – 28

Q.1- Which separation technique 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.

Ans- (a) Evaporation

(b) Sublimation

(c) Filtration

(d) Chromatography

(e) Centrifugation

(f) Separating funnel

(g) Filtration

(h) Magnetic separation

(i) Winnowing or sedimentation

(j) Decantation and filtration

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

Ans- Take a cup of water, which is a solvent, in a pan. Put some sugar, which is a solute, in it and heat it to boiling. The sugar dissolves as it is soluble in water. You will get a solution of water and sugar. Now put some tea leaves in the solution. Tea leaves are insoluble in water and will remain as residue. Boil the content and add milk. Use a strainer to get tea in a cup as filtrate and the residue will remain in the strainer.

Q.3- Pragya tested the solubility of three different substances at different temperatures and collect 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).

(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 salt?

Ans-

(a) Solubility of potassium nitrate in water at 313 K = 62 g / 100 g of water

100 g of water contains potassium nitrate at 313 K = 62 g

Therefore, 50 g of water will contain potassium nitrate at 313 K = 62/100 × 50 = 31 g

Hence, amount of potassium nitrate needed to produce a saturated solution of potassium nitrate in 50 g of water at 313 K is 31 g.

(b) She would observe the crystals of potassium chloride.

(c)

Solubility of potassium nitrate at 293 K = 32 g

Solubility of sodium chloride at 293 K = 36 g

Solubility of potassium chloride at 293 K = 35 g

Solubility of ammonium chloride at 293 K=37g

Ammonium chloride has the highest solubility at 293 K.

(d) The solubility of salt increases on increasing the temperature.

Q.4- Explain the following giving examples :

(a) Saturated solution

(b) Pure substance

(c) Colloid

(d) Suspension

Ans- (a) Saturated solution – The solution in which no more solute can be added at a given temperature is called a saturated solution.

(b) Pure substance – The substance which is made up of only single type of particles is called a pure substance. These particles are same in their chemical nature. For eg. Gold, water, sugar etc.

(c) Colloid – A colloid is a mixture in which the size of the particles lies between 1 to 100 nm. The particles of the colloids are uniformly spread throughout the solution. Due to the small size of the particles as compared to the suspension, the colloids appear to be homogeneous, but actually they are heterogeneous. For eg. milk, blood.

Suspension – It is a heterogeneous mixture in which the particles of the solute do not dissolve but remain suspended throughout the bulk of the material. The particles can be seen with the naked eyes. For eg. muddy water, chalk water.

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

Ans- Homogeneous mixture – Soda water, vinegar, filtered tea.

Heterogeneous mixture – Wood, air, soil.

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

Ans- Boil the given liquid. If its boiling point is 100°C, it is a pure water. If its boiling point is above 100°C, it is impure water. Pure substances have fixed melting and boiling points.

Q.7- Which of the following materials fall in the category of pure substances?

(a) Ice

(b) Milk

(c) Iron

(d) Hydrochloric acid

(e) Calcium oxide

(f) Mercury

(g) Brick

(h) Wood

(i) Air

Ans- (a) Ice

(b) Iron

(c) Hydrochloric acid

(d) Calcium oxide

(e) Mercury

Q.8- Identify the solutions among the following mixtures :

(a) soil

(b) sea water

(c) air

(d) coal

(e) soda water

Ans- Sea water, air and soda water.

Q.9- 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.

Q.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

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

Q.11- Which of the following are chemical changes :

(a) Growth of a plant

(b) Rusting of iron

(c) Mixing of iron fillings and sand

(d) Cooking of food

(e) Digestion of food

(f) Freezing of water

(g) Burning of candle

Ans- (a) Growth of a plant

(b) Rusting of iron

(c) Cooking of food

(d) Digestion of food

(e) Burning of candle