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.

Question - 2 : -
List the points of differences between homogeneous and heterogeneous mixtures.

Answer - 2 : -

Homogeneous mixture	Heterogeneous mixture
Particles are uniformly distributed throughout the mixture	All the particles are completely mixed and can be distinguished with the bare eyes or under a microscope.
Has a uniform composition	Irregular composition
No apparent boundaries of division	Noticeable boundaries of division.

Question - 3 : -
Differentiate between homogeneous and heterogeneous mixtures with examples.

Answer - 3 : -

The following are the differences between heterogeneous and homogenous mixtures.

Heterogeneous mixture	Homogeneous mixture
All the particles are completely mixed and can be distinguished with the bare eyes or under a microscope.	Particles are uniformly distributed throughout the mixture
Irregular composition	Has a uniform composition
Noticeable boundaries of division.	No apparent boundaries of division
Example: seawater, blood, etc.	Example: rainwater, vinegar, etc.

Question - 4 : -
How are sol, solution and suspension different from each other?

Answer - 4 : -

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

Question - 5 : -
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.

Answer - 5 : -

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

Question - 6 : -
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

Answer - 6 : -

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

Question - 7 : -
Try segregating the things around you as pure substances or mixtures.

Answer - 7 : -

Pure substance: Water, salt, sugar

Mixture: Saltwater, soil, wood, air, cold drink, rubber, sponge, fog, milk, butter, clothes, food

Question - 8 : -
What type of mixtures is separated by the technique of crystallization?

Answer - 8 : -

By the technique of crystallization, pure solids are separated from impurities. For example, salt obtained from the sea is separated from impurities; crystals of alum (Phitkari) are separated from impure samples.

Question - 9 : -
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.

Answer - 9 : -

(a) Sodium chloride from its solution in water → Evaporation

(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride → Sublimation

(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

Question - 10 : -
Write the steps you would use for making tea. Use the words: solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.

Answer - 10 : -

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 tothe filtrate, which dissolves in the filtrate. The resulting solution is the required tea.

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Chapter 2 Is Matter Around Us Pure Solutions

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