Matter- Nature and Behaviour – NCERT Exercise – 3
Question 11. Write the steps that you would use for making tea. Use the words solution, solvent, solute dissolve, soluble, insoluble, filtrate and residue.
Answer.
In making tea various steps involved are:
(i) Put some water (solvent) in a pan and put the pan containing water on a lighted gas burner
(ii) After sometime water (solvent) begins to boil, now add appropriate amount of milk and sugar (both milk and sugar are solutes)
(iii) Now stir the contents of the pan with the help of a tea spoon. The sugar (solute) will dissolve and milk will become miscible with water (solvent) A solution is thus formed.
(iv) On further boiling the solution, solute (sugar) gets completely dissolved.
(v) Now add the appropriate amount of tea leaves (solute) to the above solution in the pan. Boil and filter through a sieve. Tea will be collected as filtrate and tea leaves will get collected on sieve as residue.
Question 12. 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 solutions)
| Substance dissolved | Temperature in K |
| 283 293 313 333 353 | |
| Solubility | |
| Potassium nitrate | 21 32 62 106 167 |
| Sodium chloride | 36 36 36 7 37 |
| Potassium chloride | 35 35 40 46 54 |
| Ammonium chloride | 24 37 41 55 66 |
(a) What mass of potassium nitrate would be needed to produce a saturated solution of potassium nitrate in 50 grams of water at 313K?
Answer (a).
The amount of potassium nitrate present in 100 grams of water in a saturated solution of potassium nitrate = 62 g. (from table)
(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.
Answer (b).
If a saturated solution of potassium chloride, which is prepared at 353 K, is allowed to cool to room temperature (298 K), some of it will separate out and will settle down at the bottom of solution (we can see from the table that the solubility of potassium chloride is less at 298 K than at 353-K). Thus, we would observe a white residue at the bottom of the container.
(c) Find the solubility of each salt at 293 K. Which salt has the maximum solubility at this temperature ?
Answer (c).
From the given table we find solubility (the maximum amount of salt that can be dissolved in 100 g of water) of various salts as solubility at 293 K.
solubility of potassium nitrate in 100 g of water = 32 g
solubility of sodium chloride in 100 g of water = 36 g
solubility of potassium chloride in 100 g of water = 35g
solubility of ammonium chloride in 100 g of solubility water = 37 g Thus, we find that at 293 K the solubility of ammonium chloride in water is maximum (37g/100gofwater).
(d) What is the effect of change of temperature on the solubility of a salt?
Answer (d).
with increase of temperature, the solubility of all the given salts increases and it decreases with a decrease in temperature. [This is quite evident from the data given in table].
Question 13. Explain the following, giving examples:
(a) Saturated solution
Answer (a).
Saturated solution: A solution in which no 6. more solute can be dissolved at the same temperature is called a saturated solution Ans. e.g. a solution of sugar in water. At room temperature if any more sugar added to it, it does not dissolved but gets settled at the bottom.
(b) Pure substance
Answer (b).
Pure substance: A pure substance means a single substance (or matter) which can not be separated into other known kinds of matter by any physical process.
The substances, which always have the same colour, taste or texture at a given temperature, are pure substances, e.g. elements and components, ghee, oil, etc.
(c) Colloid
Answer (c).
Colloid: It is a type of solution in which the diameter of particle(solute particles) may range from 1 to 100 nm (nm = nanometer = 10-9m). The particles of a colloidal solution do not settle down under the force of gravity
even on standing for long time. The particles of a colloid are uniformly spread
through out the solution.
Due to smaller size particles the solution appears to be homogeneous but actually a colloidal solution is a heterogeneous mixture e.g. milk.
(d) Suspension.
Answer (d).
Suspension: It is a heterogeneous mixture in which the solid particles are spreads through out the liquid without dissolving in it. These particles get settled as a precipitate if suspension is left undisturbed for some time, e.g. muddy water, milk of magnesia, some paints etc.
[Note: The particle size of suspended particles in a suspension is more than 10-7m.]
Question 14. Classify each of the following as a homogeneous or heterogeneous mixture:
(a) Soda water
Answer. (a) Homogeneous mixture
(b) Wood
Answer (b) Heterogeneous mixture
(c) Air
Answer (c) Homogeneous mixture
(d) Soil
Answer (d) Heterogeneous mixtur
(e) Vinegar
Answer (e) Homogeneous mixture
(f) Filtered tea.
Answer (f) Homogeneous mixture.
Question 15. How would you confirm that a colourless liquid given to you is pure water?
Answer.
To confirm whether the colourless liquid given is pure or not? We can proceed as follows:
(i) Filter the given liquid using a very fine filter paper to see if it contains any suspended impurities. If any thing is left on filter paper the given liquid is impure. Otherwise it is pure.
(ii) Evaporate a part of the given liquid in a china dish. If any residue is left it is impure and in case no residue is left it is pure.
(iii) Determine the b. p. of the given liquid. If the b. p. is 100°C (373 K) it is pure water. [Note: B.P. of pure water is 373 K at 1 atmospheric pressure]
Question 16. Which of the following materials fall in the category of pure substances?
(a) Ice
Answer. (a)
Ice: Pure substance (It is pure water in solid state) It is a component.
(b) Milk
Answer (b).
Milk: It is a heterogeneous mixture. Mixtures are impure substance. Milk is a colloid.
(c) Iron
Answer (c).
Iron: Pure substance (It is an elements)
(d) Hydrochloric acid
Answer (d).
Hydrochloric acid: It is an impure substance. It is a homogeneous mixture. It is a solution of gas in a liquid.
(e) Calcium Oxide
Answer (e).
Calcium oxide: It is a pure substance (It is a compound)
(f) Mercury
Answer (f).
Mercury: It is a pure substance (It is an elements)
(g) Brick
Answer (g).
Brick: Heterogeneous mixture so impure substance.
(h) Wood
Answer (h).
Wood: Heterogeneous mixture so impure substance.
(i) Air.
Answer (i).
Air: It is homogeneous mixture so impure substance.
Question 17. Identify the solution among the following mixture:
(a) Soil
Answer (a).
Soil is not a solution. It is not a homogeneous mixture.
(b) Sea water
Answer (b).
Sea water is a solution. It is a homogeneous mixture.
(c) Air
Answer (c).
Air is a solution. It is a homogeneous mixture.
(d) Coal
Answer (d).
Coal is not a homogeneous mixture so it is not a solution.
(e) Soda water
Answer (e).
Soda water is a homogeneous mixture so it is a solution.
[A solution is a homogeneous mixture]
Question 18. Which of the following will show “Tyndall effect”
(a) Salt solution
(b) Milk
(c) Copper sulphate solution
(d) Starch sol.
Answer. “Tyndall effect” is shown by colloidal solution. So, it will be shown by milk, starch sol and not by salt solution, copper sulphate solution is a true solutions and not colloidal solution.
Question 19. Classify the following into elements compounds and mixtures:
(a) Sodium
(b) Soil
(c) Sugar solution
(d) Silver
(e) Calcium carbonate
(f) Zinc
(g) Silicon
(h) Coal
(i) Air
(j) Soap
(k) Methane
(l) Carbon dioxide
(m) Blood.
Answer.
(a) element
(b) mixture (heterogeneous mixture)
(c) mixture (homogeneous mixture)
(d) element
(e) compound (CaCO3)
(f) element
(g) element
(h) mixture (heterogeneous mixture)
(i) mixture (homogeneous mixture)
(j) mixture
(k) Compound (CH4)
(l) Compound (CO2)
(m) mixture
Question 20. Which of the following are chemical changes ?
(a) growth of a plant
Answer (a).
It is a chemical change.
(b) rusting of iron
Answer (b)
It is a chemical change
(c) mixing of iron filings and sand
Answer (c)
It is a physical change
(d) cooking of food
Answer (d)
It is a chemical change
(e) digestion of food
Answer (e)
It is a chemical change
(f) freezing of water
Answer (f)
It is a physical change
(g) burning of a candle.
Answer (g)
It is a chemical change.