Is Matter Around Us Pure

1. 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.

Mass of solute (sodium chloride) = 36 g

Mass of solvent (water) = 100 g

Mass of solution = Mass of solute + Mass of solvent

= 36 g + 100 g = 136 g

Concentration = Mass of solute/Mass of solution x 100

=36/136x100=26.47%

2. Name the technique to separate

(i) butter from curd,

(ii) salt from sea-water,

(iii) camphor from salt.

(i) Centrifugation

(ii) Evaporation,

(iii) Sublimation

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

Crystallisation technique is used to purify solid with some impurities in it. Example: Salt from sea-water.

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

Pure substances—Water, bread, sugar and gold.

Mixtures—Steel, plastic, paper, talc, milk and air

5. 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.

(a) Evaporation

(b) Sublimation

(c) Filtration

(d) Chromatography

(e) Centrifugation

(f) Separating funnel

(g) Filtration

(h) Magnetic separation

(i) Winnowing/ sedimentation

(j) Decantation and filtration

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

1. Take a cup of water in a container as solvent and heat it.

2. Add sugar in it which is solute. Heat it till all sugar dissolves.

3. You get a solution of water and sugar.

4. Sugar is soluble in water completely.

5. Add half a tea-spoon of tea-leaves, it is insoluble in water.

6. Boil the content, add milk which is also soluble in water, boil again.

7. Filter the tea with the help of strainer, the tea collected in cup is filtrate and the tea leaves collected on the strainer is residue.

7. Explain the following giving examples:

(a) Saturated solution

(b) Pure substance

(c) Colloid

(d) Suspension

(a) Saturated solution:

In a given solvent when no more solute can dissolve further at a given temperature is called saturated solution.

(b) Pure substance:

A pure substance consists of a single type of particles. E.g., gold, silver.

(c) Colloid:

A colloid is a solution in which the size of solute particles are bigger than that of true solution. These particles cannot be seen with our naked eyes, they are stable, e.g., ink, blood.

(d) Suspension:

It is a heterogeneous mixture in which the solute particles are big enough to settle down, e.g., chalk-water, paints, etc.

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

Homogeneous:

Soda water, vinegar, filtered tea.

Heterogeneous:

Wood, air, soil.

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

By finding the boiling point of a given colourless liquid. If the liquid boils at 100°C at atmospheric pressure, then it is pure water. This is because pure substances have fixed melting and boiling point.

10. 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) Back (h) Wood (i) Air.

Pure substances are: Ice, iron, hydrochloric acid, calcium oxide and mercury.

11. Identify the solutions among the following mixtures.

(a) Soil (b) Sea water (c) Air (d) Coal (e) Soda water.

Solutions are: Sea water soda water and air.

12. Which of the following will show “Tyndall effect”?

(a) Salt solution (b) Milk (c) Copper sulphate solution (d) Starch solution.

Milk and starch solution.

13. 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 – Sugar solution

Silver – Methane – Soil

Tin – Carbon dioxide – Coal

Silicon – Soap – Air ,Blood

14. 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.

Chemical changes are:

(a) Growth of a plant (b) Rusting of iron (c) Cooking of food (d) Digestion of food (e) Burning of a candle