Intext Questions

Q.1     What is meant by a pure substance? 
Sol.      A pure substance is the one that consists of a single type of particles, i.e., all constituent particles of the substance have the same chemical nature. Pure substances can be Classified as elements or compounds.

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Q.2     List the points of differences between homogeneous and heterogeneous mixtures.
Sol.      A homogeneous mixture is a mixture having a uniform composition throughout the mixture.
For example: salt in water, sugar in water, copper sulphate in water A heterogeneous mixture is a mixture having a non-uniform composition throughout the mixture. For example: sodium chloride and iron fillings, salt and sulphur, oil and water

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Q.1     Differentiate between homogeneous and heterogeneous mixtures with examples.
Sol.      A homogeneous mixture is a mixture having a uniform composition throughout the mixture. For
example, mixtures of salt in water, sugar in water, copper sulphate in water, iodine in alcohol, alloy, and
air have uniform compositions throughout the mixtures. On the other hand, a heterogeneous mixture is a mixture having a non-uniform composition throughout the mixture. For example, composition of mixtures of sodium chloride and iron fillings, salt and sulphur, oil and water, chalk powder in water, wheat flour in water, milk and water are not uniform through out
the mixtures.

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Q.2     How are sol, solution and suspension different from each other?
Sol.      is a heterogeneous mixture. In this mixture, the solute particles are so small that they cannot be seen with the naked eye. Also, they seem to be spread uniformly throughout the mixture. The Tyndall effect is observed in this mixture.For example: milk of magnesia, mud Solution is a homogeneous mixture. In this mixture, the solute particles dissolve and spread uniformly throughout the mixture. The Tyndall effect is not observed in this mixture. For example: salt in water, sugar in water, iodine in
alcohol, alloy Suspensions are heterogeneous mixtures. In this mixture, the solute particles are visible to the naked eye, and remain suspended throughout the bulk of the medium. The Tyndall effect is observed in this mixture. For example: chalk powder and water, wheat flour and water

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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.
Sol.     Mass of solute (sodium chloride) = 36 g (Given)
Mass of solvent (water) = 100 g (Given)
Then, mass of solution= Mass of solute + Mass of solvent
= (36 + 100) g
= 136 g
Therefore, concentration (mass by mass percentage) of the solution
=MassofsoluteMassofsolvent×100%
=36136×100%
= 26.47 %

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Q.1     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?
Sol.     A mixture of two miscible liquids having a difference in their boiling points more than 25°C can be separated by the method of distillation. Thus, kerosene and petrol can be separated by distillation.


In this method, the mixture of kerosene and petrol is taken in a distillation flask with a thermometer
fitted in it. We also need a beaker, a water condenser, and a Bunsen burner. The apparatus is arranged as shown in the above figure. Then, the mixture is heated slowly. The thermometer should be watched
simultaneously. Kerosene will vaporize and condense in the water condenser. The condensed kerosene is
collected from the condenser outlet, whereas petrol is left behind in the distillation flask.

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Q.2     Name the technique to separate
           (i) butter from curd
           (ii) salt from sea-water
           (iii) camphor from salt
Sol.     (i) Butter can be separated from curd by centrifugation.
(ii) Salt can be separated from sea-water by evaporation.
(iii) Camphor can be separated from salt by sublimation.

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Q.3     What type of mixtures is separated by the technique of crystallization?
Sol.     By the technique of crystallization, pure solids are separated from impurities. For example, salt obtained from sea is separated from impurities; crystals of alum (Phitkari) are separated fromimpure samples.

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

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Q.2     Try segregating the things around you as pure substances or mixtures.
Sol.     Pure substance: Water, salt, sugar Mixture: Salt water, soil, wood, air, cold drink, rubber, sponge, fog, milk, butter, clothes, food

 

Exercise

Q.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 ϐlower 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.
Sol.     (a) Sodium chloride from its solution in water → Evaporation
(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride →
Sublimation
(c) Small pieces of metal in the engine oil of a car → Centrifugation or filtration or decantation
(d) Different pigments from an extract of flower petals → Chromatography
(e) Butter from curd → Centrifugation
(f ) Oil from water → Using 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

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Q.2     Write the steps you would use for making tea. Use the words: solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
Sol.      First, water is taken as a solvent in a saucer pan. This water (solvent) is allowed to boil. During heating, milk and tea leaves are added to the solvent as solutes. They form a solution. Then, the solution is poured through a strainer. The insoluble part of the solution remains on the strainer as residue. Sugar is added to the filtrate, which dissolves in the filtrate. The resulting solution is the required tea.

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Q.4     Explain the following giving examples:
           (a) Saturated solution
           (b) Pure substance
           (c) Colloid
           (d) Suspension
Sol.     (a) Saturated solution
A saturated solution is a solution in which the maximum amount of solute has been dissolved at a given temperature. The solution cannot dissolve beyond that amount of solute at that temperature. Any more solute added will settle down at the bottom of the container as a precipitate. Suppose 500 g of a solvent can dissolve a maximum of 150 g of a particular solute at 40°C. Then, the solution obtained by dissolving 150 g of that solute in 500 g of that solvent at 300 K is said to be a saturated solution at 300 K.
(b) Pure substance A pure substance is a substance consisting of a single type of particles i.e., all constituent particles of the substance have the same chemical properties. For example, salt, sugar, water are pure substances.
(c) Colloid A colloid is a heterogeneous mixture. The size of the solutes in this mixture is so small that they cannot be seen individually with naked eyes, and seems to be distributed uniformly throughout the mixture. The solute particles do not settle down when the mixture is left undisturbed. This means that colloids are quite stable. Colloids cannot be separated by the process of filtration. They can be separated by centrifugation. Colloids show the Tyndall effect. For example, milk, butter, foam,fog, smoke, clouds.
(d) Suspension Suspensions are heterogeneous mixtures. The solute particles in this mixture remain suspended throughout the bulk of the medium. The particles can be seen with naked eyes. Suspension shows the Tyndall effect. The solute particles settle down when the mixture is left undisturbed. This means that suspensions are unstable. Suspensions can be separated by the method of filtration. For example, mixtures of chalk powder and water, wheat ϐlour and water.

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Q.5     Classify each of the following as a homogeneous or heterogeneous mixture. Soda water,wood, air, soil, vinegar, filtered tea
Sol.      Homogeneous mixtures: Soda water, air, vinegar
Heterogeneous mixtures: Wood, soil, filtered tea

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Q.6     How would you confirm that a colour less liquid given to you is pure water?
Sol.      Every liquid has a characteristic boiling point. Pure water has a boiling point of 100°C (373 K) at 1 atmospheric pressure. If the given colour less liquid boils at even slightly above or below 100°C, then the given liquid is not pure water. It must boil at sharp 100°C. Thus, by observing the boiling point, we can confirm whether a given colour less liquid is pure water or not.

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Q.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
Sol.     The following materials fall in the category of a “pure substance”:
(a) Ice
(c) Iron
(d) Hydrochloric acid
(e) Calcium oxide
(f ) Mercury

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

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Q.9     Which of the following will show the “Tyndall effect”?
           (a) Salt solution
           (b) Milk
           (c) Copper sulphate solution
           (d) Starch solution
Sol.     Milk and starch solution will show the “Tyndall effect”.

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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
Sol.        Elements
(a) Sodium
(d) Silver
(f ) Tin
(g) Silicon
(e) Calcium carbonate
(k) Methane
(l) Carbon dioxide
Mixtures
(b) Soil
(c) Sugar solution
(h) Coal
(i) Air
(j) Soap
(m) Blood

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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
Sol.        The following changes are chemical changes:
(a) Growth of a plant
(b) Rusting of iron
(d) Cooking of food
(e) Digestion of food
(g) Burning of candle

Exemplar

Multiple Choice Questions : 

Q.1 Which of the following statements are true for pure substances?

(i) Pure substances contain only one kind of particles

(ii) Pure substances may be compounds or mixtures

(iii) Pure substances have the same composition throughout

(iv) Pure substances can be exemplified by all elements other than nickel

(a) (i) and (ii)

(b) (i) and (iii)

(c) (iii) and (iv)

(d) (ii) and (iii)

Sol. (b) (i) and (iii)

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Q.2 Rusting of an article made up of iron is called

(a) Corrosion and it is a physical as well as chemical change

(b) Dissolution and it is a physical change

(c) Corrosion and it is a chemical change

(d) Dissolution and it is a chemical change

Sol. (c) Corrosion and it is a chemical change

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Q.3 A mixture of sulphur and carbon disulphide is

(a) Heterogeneous and shows Tyndall effect

(b) Homogeneous and shows Tyndall effect

(c) Heterogeneous and does not show Tyndall effect

(d) Homogeneous and does not show Tyndall effect

Sol. (a) Heterogeneous and shows Tyndall effect

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Q.4 Tincture of iodine has antiseptic properties. This solution is made by dissolving

(a) Iodine in potassium iodide

(b) Iodine in vase line

(c) Iodine in water

(d) Iodine in alcohol

Sol. (c) Iodine in water

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Q.5 Which of the following are homogeneous in nature?

(i) ice

(ii) wood

(iii) soil

(iv) air

(a) (i) and (iii)

(b) (ii) and (iv)

(c) (i) and (iv)

(d) (iii) and (iv)

Sol. (c) (i) and (iv)

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Q.6 Which of the following are physical changes?

(i) Melting of iron metal

(ii) Rusting of iron

(iii) Bending of an iron rod

(iv) Drawing a wire of iron metal

(a) (i), (ii) and (iii)

(b) (i), (ii) and (iv)

(c) (i), (iii) and (iv)

(d) (ii), (iii) and (iv)

Sol. (c) (i), (iii) and (iv)

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Q.7 Which of the following are chemical changes?

(i) Decaying of wood

(ii) Burning of wood

(iii) Sawing of wood

(iv) Hammering of a nail into a piece of wood

(a) (i) and (ii)

(b) (ii) and (iii)

(c) (iii) and (iv)

(d) (i) and (iv)

Sol. (a) (i) and (ii)

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Q.8 Two substances, A and B were made to react to form a third substance, A₂B according to the following reaction :-

2 A + B → A₂ B

Which of the following statements concerning this reaction are incorrect?

(i) The product A ₂ shows the properties of substances A and B

(ii) The product will always have a fixed composition

(iii) The product so formed cannot be classified as a compound

(iv) The product so formed is an element

(a) (i), (ii) and (iii),

(b) (ii), (iii) and (iv)

(c) (i), (iii) and (iv)

(d) (ii), (iii) and (iv)

Sol. (c) (i), (iii) and (iv)

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Q.9 Two chemical species X and Y combine together to form a product P which contains both X and Y X + Y → P

X and Y cannot be broken down into simpler substances by simple chemical reactions. Which of the following concerning the species X, Y and P are correct?

(i) P is a compound

(ii) X and Y are compounds

(iii) X and Y are elements

(iv) P has a fixed composition

(a) (i), (ii) and (iii),

(b) (i), (ii) and (iv)

(c) (ii), (iii) and (iv)

(d) (i), (iii) and (iv)

Sol. (d) (i), (iii) and (iv)