Solution of Chapter 2. Is Matter Around us Pure (NCERT - Science Book)

What is meant by a pure substance?

List the points of differences between homogeneous and heterogeneous mixtures.

Differentiate between homogeneous and heterogeneous mixtures with examples.

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

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

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?

Name the technique to separate:

(i) butter from curd.

(ii) salt from sea-water.

(iii) camphor from salt.

What type of mixtures are separated by the technique of crystallisation?

Classify the following as chemical or physical changes:

(i) cutting of trees

(ii) melting of butter in a pan

(iii) rusting of almirahs

(iv) boiling of water to form steam

(v) passing of electric current through water and the water breaking down into hydrogen and oxygen gases

(vi) dissolving common salt in water

(vii) making a fruit salad with raw fruits, and

(viii) burning of paper and wood

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

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.

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

Pragya tested the solubility of four 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).

(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 in temperature on the solubility of a salt?

Explain the following giving examples:

(a) Saturated solution

(b) Pure substance

(c) Colloid

(d) suspension

Classify each of the following as a homogeneous or heterogeneous mixture:

soda water, wood, air, soil, vinegar, filtered tea

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

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

(j) Mercury

(g) Brick

(h) Wood

(i) Air

Identify the solutions among the following mixtures:

(a) Soil

(b) Sea-water

(c) Air

(d) Coal

(e) Soda water

Which of the following will show "Tyndall effect"?

(a) Salt solution

(b) Milk

(c) Copper sulphate solution

(d) Starch solution

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

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

(j) Freezing of water

(g) Burning of a candle