Chapter 2 Is Matter Around Us Pure
Question 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 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: (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
Question 2. Write the steps you
would use for making tea. Use the words, solution, solvent, solute, dissolve,
soluble, insoluble, filtrate and residue.
Answer: 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.
Question 3. Pragya tested the
solubility of three 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 coo! at room temperature. What would she observe
us 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 a salt?
Answer:
Question 4. Explain the following
giving examples:
(a) Saturated solution
(b) Pure substance
(c) Colloid
(d) Suspension
Answer: (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.
Question 5. Classify each of the
following as a homogeneous or heterogeneous mixture: soda water, wood, air.
soil, vinegar, filtered tea.
Answer: Homogeneous: Soda water, vinegar, filtered tea.
Heterogeneous: Wood, air, soil.
Question 6. How would, you confirm
that a colourless liquid given to you is pure water?
Answer: 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.
Question 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) Back (h) Wood (i) Air.
Answer: Pure substances are: Ice, iron, hydrochloric acid, calcium
oxide and mercury.
Question 8. Identify the solutions
among the following mixtures.
(a) Soil (b) Sea water
(c) Air (d) Coal
(e) Soda water.
Answer: Solutions are: Sea water soda water and air.
Question 9. Which of the following
will show “Tyndall effect”?
(a) Salt solution (b) Milk
(c) Copper sulphate solution (d) Starch solution.
Answer: Milk and starch solution.
Question 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
Answer: Elements – Compounds – Mixtures
Sodium – Calcium carbonate – Sugar solution
Silver – Methane – Soil
Tin – Carbon dioxide – Coal
Silicon – Soap – Air ,Blood
Question 11. 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.
Answer: 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
