This post contains Question Answer of chapter Is Matter Around Us Pure including NCERT Exercise.
1. What is meant by a substance?
Sol: A substance is a kind of matter that cannot be separated into other kinds of matter by any physical process.
2. List the point of difference between homogeneous and heterogeneous mixtures.
Sol: Homogeneous mixture:
(a) Perfectly uniform in its composition.
(b) Properties throughout the mixture are the same.
Heterogeneous mixtures:
(a) Different compositions at different locations in the mixture.
(b) Properties are different at different locations in the mixture.
3. Differentiate between homogeneous and heterogeneous mixtures with examples.
Sol: A mixture which is perfectly uniform in its composition and properties throughout is called a homogeneous mixture. Homogeneous mixtures are also called solutions.
Kerosene is a homogeneous mixture of many hydrocarbons, solution of common salt or sugar in water is also a homogeneous mixture. Some common alloys, e.g., brass, are homogeneous mixtures.
A mixture which has different compositions and different properties at different locations in the mixture is called heterogeneous mixture.
Muddy water from a pond, a mixture containing sugar and sand are heterogeneous mixtures. Some other heterogeneous mixtures are a mixture consisting of sodium chloride and iron powder or filings, a mixture consisting of common salt and sulphur, a mixture consisting of an oil and water.
4. How are sol, solution and suspension different from each other?
Sol: Sol (colloid):
- A sol (colloid) is a homogeneous looking, but heterogeneous mixture.
- In a sol, the dispersed particles can be seen only with a powerful microscope.
- In a sol, the size of the particles is between 10-7 m and 10-9 m.
- The constituents of a sol cannot be separated by filtration.
Solution:
- A solution is a homogeneous mixture of two or more substances.
- In a solution, solute cannot be seen even with a powerful microscope.
- In a solution the size of the particle is about 10-10 m.
- The constituents of a solution cannot be separated by ordinary filtration.
Suspension:
- A suspension is a heterogeneous mixture of a solid dispersed in a liquid or a gas.
- In a suspension, the particle can be seen with the naked eye or simple microscope.
- In a suspension, the size of the particle is greater than 10-7 m.
- The constituent of a suspension can be separated by ordinary filtration.
5. To make a saturated solution, 36 gram of sodium chloride is dissolved in 100 gram of water at 293 K. Find its concentration at this temperature.
Sol:
6. How will you separate a mixture containing kerosene and petrol which are miscible with each other? (Difference in their boiling point is more than 25 degree Celsius)
Sol: The components of this mixture can be separated by simple distillation. Petrol will go out as distillate and kerosene will be left behind in the flask.
7. Name the techniques to separate:
(a) butter from curd (b) salt from seawater (c) camphor from salt.
Sol: (a) By churning or centrifugation
(b) By evaporation
(c) By sublimation
8. What type of mixtures are separated by the technique of crystallisation?
Sol: Mixtures containing components which differ in their solubility in any solvent, generally water, are separated by crystallisation.
9. Classify the following as chemical or physical changes:
(a) Cutting of trees
(b) Melting of butter in a pan
(c) Rusting of iron almirah
(d) Boiling of water to form steam
(e) Passing of electric current through water and the water breaking down into hydrogen and oxygen gases
(f) Dissolving common salt in water
(g) Making a fruit salad from raw fruits
(h) Burning of paper and wood.
Sol: Chemical change: (a), (b), (c), (e), (h)
Physical change: (d), (f), (g)
10. Try segregating the things around us as pure substances or mixtures.
Sol: Substances: Distilled water, Sugar, Sulphur, Iron, Gold.
Mixtures: Air, Aerated liquids, Black ink, Milk.
11. 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 pin from sand.
(i) Wheat grain from husk.
(j) Fine mud particles suspended in water.
Sol: (a) Evaporation
(b) Sublimation
(c) Magnetic separation method
(d) Chromatography
(e) Churning
(f) Separating funnel method
(g) Filtration
(h) Magnetic separation method
(i) Winnowing
(j) Loading, Sedimentation, Filtration
12. Write the steps you would use for making tea. Use the words solution, solvent, solute, dissolve, soluble, insoluble, filtrate and residue.
Sol: The steps involved in making of tea are:
- Boil water – Solvent
- Add tea leaves – Solute
- Filter through a tea strainer.
- Tea leaves left in the strainer – Insoluble component or residue
- Filtrate – Tea water solution (Soluble components dissolves).
13. 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 gram of substances dissolved in hundred gram 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 observed 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 of temperature on the solubility of a salt?
Sol: (a) Mass of potassium nitrate would be needed to obtain a saturated solution in 50 gram at 373 K = (62g x 50 g)/(100 g) = 31 g
(b) On cooling, crystals of potassium chloride will separate out. This is because of decrease in the solubility of potassium chloride with the fall in temperature.
(c) The solubility of the given solids at 293 K are:
From the data, Ammonium chloride has the highest solubility.
(d) The solubility of the salt increases with the rise in temperature. However, the solubility of sodium chloride changes very little with the rise in temperature.
14. Explain the following giving examples:
(a) Saturated solution (b) Pure substance (c) Colloid (d) Suspension
Sol: (a) A solution in which no more solute is dissolved at any fixed temperature is called a saturated solution. In other words, a solution which contain maximum possible amount of solute at any given temperature is called a saturated solution, e.g., a saturated solution of sodium chloride.
(b) A sample of matter containing only one substance is called a pure substance,e.g., iron, sucrose, water, sodium chloride.
(c) A, homogeneous-looking, heterogeneous mixture in which particles having size between 1nm and 100 nm are dispersed in a continuous medium is called a colloid, e.g., milk.
(d) A suspension is a heterogeneous mixture in which very fine particles of a solid, greater than 100 nm in size, are dispersed in any medium, either liquid or gas. In any suspension, fine particles of the solid remain suspended in the medium, e.g., muddy pond water, smoke coming out of a chimney of a factory, chalk-water mixture.
15. Classify each of the following as a homogeneous or heterogeneous mixture: soda water. wood, air, soil, vinegar, filtered tea.
Sol: Homogeneous mixture: Soda water, Air (clean with no impurity), Vinegar, Filter tea.
Heterogeneous mixture: Wood, Air (containing dust or smoke particles), Soil.
16. How would you confirm that a colourless liquid given to you is a pure water?
Sol: The purity of water can be conferred confirmed by determining its boiling point. At normal temperature, pure water boils at 100°C or 373 K.
17. Which of the following material fall in the category of a pure substance: Ice, Milk, Iron, Hydrochloric acid, Calcium oxide, Mercury, Brick, Wood and Air?
Sol: The following are the pure substances: Ice, Iron, Calcium oxide, Mercury.
18. Identify solutions among the following mixtures: Soil, Sea water, Air, Coal, Soda water?
Sol: The following are the solutions: Sea water, Soda water.
19. Which of the following will show Tyndall effect: Salt solution, Milk, Copper sulphate solution, Starch solution?
Sol: Solution which show tyndall effect are: Milk and Starch solution.
20. Classify the following into elements, compounds or mixtures: Sodium, Soil, Sugar solution, Silver, Calcium carbonate, Tin, Silicon, Coal, Air, Soap, Methane, Carbon dioxide and Blood.
Sol: The classification into elements, compounds and mixtures is given below:
Elements: Sodium, Silver, Tin and Silicon.
Compound: Calcium carbonate, Methane and Carbon dioxide.
Mixture: Soil, Sugar solution, Coal, Air, Soap and Blood.
21. Which of the following are chemical changes: Growth of a plant, Rusting of iron, Mixing of iron filings and sand, Cooking of food, Digestion of food, Freezing of water, Burning of a candle?
Sol: Following are the chemical changes: Growth of a plant, Rusting of iron, Cooking of food, Digestion of food, Burning of a candle.
22. Sucrose (sugar) crystal obtained from sugarcane and beetroot are mixed together. Will it be a pure substance or mixture? Give reason for the same.
Sol: it will be a pure substance because the chemical composition of sugar is the same whatever be its source.
23. Name the properties which can be used for testing the purity of a substance.
Sol: Purity of substance can be checked by determining any of the following properties:
(a) Melting point (b) Boiling point (c) Density (d) Refractive index.
24. Mention one each of the following types of mixtures: (a) gas in gas type (b) liquid in liquid type (c) solid and liquid type (d) gas in liquid type.
Sol: (a) Air (b) Alcohol in water (c) Sugar in water (d) Aerated water (solution of carbon dioxide in water)
25. Some solids dissolve easily in liquids, while the others do not.
(a) What is the name given to the liquid which dissolve solids?
(b) What is the name given to the clear liquid formed when a solid dissolves in liquid?
(c) What is the name given to the liquid which contains in it some suspended particles?
Sol: (a) The liquid which dissolves solids is called solvent.
(b) The clear liquid formed when a solid dissolves in liquid is called solution.
(c) The liquid which contains some suspended particles is called suspension.
26. The teacher instructed three students ‘A’, ‘B’ and ‘C’ respectively to prepare 50% (mass by volume) solution of sodium hydroxide. ‘A’ dissolves 50 g of NaOH in 100 ml of water, ‘B’ dissolved 50 gram of NaOH in 100 g of water while ‘C’ dissolved 50 g of NaOH in water to make 100 ml of solution. Which one of them has made the desired solution and why?
Sol: The student ‘C’ has made the desert solution.
27. During an experiment the students were asked to prepare 10% (mass by mass) solution of sugar in water. Ramesh dissolved 10 g of sugar in 100 g of water, while Sarika prepared it by dissolving 10 g of sugar in water to make 100 g of the solution.
(a) Are the two solutions of the same concentration?
(b) Compare the mass percent of the two solutions.
Sol: (a) No, the two solutions have different concentration on mass by mass basis.
(b) Solution prepared by Ramesh:
Solution prepared by Sarika:
28. You are given two samples of water labelled as ‘A’ and ‘B’. Sample ‘A’ boils at 100°C and sample ‘B’ boils at 102°C. Which sample of water will not freeze at 0°C? Comment.
Sol: Sample ‘B’ having boiling point of 102°C will not freeze freeze at 0°C. Since the boiling point of sample ‘B’ is above 100°C, hence its freezing point will be below 0°C.
29. Air contains about 0.03% of carbon dioxide. Calculate its concentration in parts per million (ppm) units.
Sol: Number of parts of carbon dioxide in hundred parts of air = 0.03
106 parts of the air = (0.03/100)*106 = 300 ppm.
30. Explain why particles of a colloid solution do not settle down when left undisturbed, while in the case of suspension they do.
Sol: The particles in a colloidal solution are very small and light. Under the bombardment of the solvent molecules, the colloidal particles keep moving around in the medium. The particles in a suspension are large and heavier. These particle settle down due to gravitational pull.
31. Smoke and fog both are aerosols. In what way are they different?
Sol: Smoke is an aerosol in which fine solid particles are dispersed in the air. In fog, small droplets of water are dispersed in the air.
32. Write answer for the following terms for a colloidal solution: Nature, particle size, filtrability, stability and light scattering.
Sol: Nature: Heterogeneous
Particle size: Between 1 nm to 100 nm
Filtrability: Unfiltrable (colloidal particle cannot be separated by filtration)
Stability: Unstable (particles tends to form aggregate)
Light scattering: Colloids scatter light, show tyndall effect.
33. The dispersed particles in a colloidal solution show the motion under an electric field as shown in the figure alongside.
(a) What is the phenomenon called?
(b) What is the nature of charge on the particles?
(c) In which direction does the solvent migrate?
Sol: (a) Electrophoresis
(b) Negative charge
(c) Towards negative electrode.
34. You are provided with a mixture containing sand, iron fillings, ammonium chloride and sodium chloride. Describe the procedures you would use to separate these constituents from the mixture?
Sol: Follow the steps given below:
- Separate iron filings with the help of a magnet.
- Separate ammonium chloride by sublimation.
- Add a small quantity of water to the remaining mixture, stir it and then filter. Collect the filtrate in a China dish.
- Evaporate the filtrate. The dry mass left in the China dish is sodium chloride.
- The residue left on the filter paper cone is wet sand, and dried in air.
35. While using a bar magnet for separating iron filling over a mixture of sand and iron filings, which pole of magnet is moved over the mixture?
Sol: Any pole of the bar magnet can be moved over the mixture. Both the poles of a magnet show the property of attracting iron.
36. When an impure sample of camphor is sublimed, where do you get pure camphor?
Sol: Pure camphor is obtained as a deposit on the inner walls of the funnel.
37. After the winter is over, a generally pack of our woollens with mothballs. These mothballs disappear slowly. What type of change is involved in this process?
Sol: Mothballs are made from a chemical compound called naphthalene. Under normal condition of temperature and pressure, it undergoes sublimation. Thus, solid mothballs slowly get converted into vapour. These vapours slowly escape to the atmosphere. As the disappearance of mothballs involve a change of solid chemical compound into its vapour. It is a physical change.
38. Solid carbon dioxide, known as dry ice, when kept in a plate at room temperature disappears after sometime. It neither wet the plate nor leave any ash behind. Explain this observation. Name the phenomenon responsible for this behaviour of dry ice.
Sol: Solid carbon dioxide, under room temperature conditions, sublimes to give carbon dioxide gas that escapes into the atmosphere. That’s why it neither wets the plate nor leave any ash.
39. Why tea-strainer cannot be used for filtering muddy water?
Sol: Because the pores is tea-strainer are much bigger than size the particle in muddy water.
40. During crystallisation, the crystals are present alongwith a liquid in a china dish or beaker.
(a) By what name is the liquid called?
(b) How are the crystal separated from the liquid?
(c) Where do the soluble impurities remain?
Sol: (a) The liquid is called mother liquor.
(b) Crystals are separated from the mother liquor, with the help of a spatula.
(c) Soluble impurities are left behind in the mother liquor.
41. A small quantity of filtered copper sulphate solution is evaporated in a china dish to get a saturated solution. The saturated solution is left undisturbed at room temperature for a day.
(a) What do you observe in the china dish?
(b) Do all crystal look alike?
(c) Do crystals differ in size?
(d) How will you separate the crystals from the liquid in the china dish?
(e) What is the name of the liquid left behind after the crystals are separated?
Sol: (a) Small crystals, blue in colour, starts forming.
(b) All the crystals are blue and look alike, but differ in size.
(c) Yes, crystals differ in size.
(d) Crystals are separated from the liquid by decantation.
(e) The liquid left behind after crystallisation is called mother liquor.
42. Two groups of students are given 5 g of iron fillings and 3 gram of sulphur powder each. Group ‘A’ is asked to mix and crush the mixture. Group ‘B’ is asked to mix, crush and heat the mixture strongly. The resulting molten mass is then left to cool. Both the groups were then asked to study the following properties:
I. Magnetic property
II. The texture and colour
III. Solubility in carbon disulfide
IV. Action of dilute sulphuric acid or dilute hydrochloric acid
Now, answer the following questions:
(a) Did the material obtained by two groups look the same?
(b) Which group did obtain a material with magnetic property?
(c) Can we separate the components of the material obtained?
(d) On adding dilute sulphuric or with dilute hydrochloric acid, did both the groups obtain a gas?
(e) Did the gas in both the cases smell the same or different?
Sol: (a) No
(b) Group ‘A’ will obtain a new material with magnetic properties.
(c) The components of material obtained by group ‘A’ can be separated. The components of material obtained by group ‘B’ cannot be separated.
(d) Yes
(e) The gases obtained in the two cases smells differently.
The gas obtained for the sample obtained by group ‘A’ is odourless. The gas obtained for the sample obtained by group ‘B’ smells like rotten eggs.
43. Iron filings and sulphur were mixed together and divided into two parts, ‘A’ and ‘B’. Part ‘A’ was heated strongly while part ‘B’ was not heated. Dilute hydrochloric acid was added to both the parts and evolution of gas was seen in both the cases. How will you identify the gases evolved?
Sol: Part ‘A’ of the mixture on heating gives iron(II) sulphide.
Part ‘B’ of the mixture contains only sulphur and iron fillings.
On reaction with dilute hydrochloric acid, the gas is given by the two samples are:
Part ‘A’ gives hydrogen sulphide gas which smell of rotten eggs and turns lead acetate paper black.
Part ‘B’ gives hydrogen gas, which gives pop sound.
44. What would you observe when-
(a) a saturated solution of potassium chloride prepared at 60°C is allowed to cool at room temperature.
(b) an aqueous sugar solution is heated to dryness.
(c) a mixture of iron filings and sulphur powder is heated strongly.
Sol: (a) The crystals of potassium chloride will separate out.
(b) The solution will lose water and get concentrated. When heating is continued after dryness, the sugar will get charred to give brownish-black mass.
(c) Blackish compound, iron(II) sulphide, is formed.
45. Four different mixtures in water are prepared using charcoal powder, chalk powder, slaked lime and detergent powder. Which of these:
(a) Would not leave residue on filter paper after filtration?
(b) Would show tyndall effect?
(c) Would leave residue on filter paper after filtration?
(d) Would give transparent or clear solution?
Sol: (a) Detergent solution and slaked lime solution will not leave any residue on filter paper after filtration.
(b) Detergent solution will show tyndall effect.
(c) Charcoal powder and chalk powder will leave residue on filter paper.
(d) Slaked lime will give transparent or clear solution.
46. Name the process associated with the following:
(a) Dry ice is kept at room temperature and at one atmospheric pressure.
(b) A drop of ink placed on the surface of water contained in a glass spreads through the water.
(c) A potassium permanganate crystal is in beaker and water is poured into the beaker with stirring.
(d) A acetone bottle is left open and the bottle become empty after some time.
(e) Milk is churned to separate cream from it.
(f) Settling of sand when a mixture of sand and water is left undisturbed for sometime.
(g) Fine beam of light entering through a hole in a dark room, illuminates the particles in its paths.
Sol: (a) Sublimation
(b) Diffusion
(c) Dissolution
(d) Evaporation
(e) Centrifugation
(f) Sedimentation
(g) Scattering of light or Tyndall effect.
47. Comment upon the statement that burning of a candle involves both physical and chemical changes. Sol: When we light a candle, there are two changes which take place. These are:
(a) Melting of wax
(b) Burning of the thread and wax.
The melting of wax is a physical change, while the burning of thread and wax is a chemical change. So, the burning of a candle involves both physical as well as chemical changes.
48. On heating, calcium carbonate gets converted into calcium oxide and carbon dioxide.
(a) Is this a physical or chemical change?
(b) Can you prepare for one acidic and one basic solution by using the product formed in the above process? If so, write the chemical equation involved.
Sol: (a) Chemical change
(b) Acidic solution: By dissolving carbon dioxide and water.
CO2 + H2O → H2CO3
CaO + H2O → Ca(OH)2
Basic solution: By dissolving calcium oxide in water.
49. In every chemical reaction of a substance X, the mass of the product obtained is greater than the mass of X taken for the reaction. What kind of the substance is X?
Sol: The substance X is an element. Whenever an element take part in a reaction, it combines with some other elements. This leads to an increase in the mass.
50. Two substances A and B were made to react to form a third substance, A2B according to the following reaction: 2A + B → A2B
Which of the following statements concerning this reaction are incorrect?
I. The product A2B show the properties of substance A and B.
II. The product will always have a fixed composition.
III. The products of formed cannot be classified as a compound.
IV. The product so formed is an element.
(a) I, II and III
(b) II, III and IV
(c) I, III and IV
(d) I, II and IV
Sol: The correct choice is (c). The statement I, III and IV are incorrect.
51. Substances X and Y are made to react to form a new substance Z. The following observations were made:
(a) During the reaction between X and Y, a large amount of heat is evolved.
(b) The properties of Z are different from those of X and Y.
What type of substance is Z? Give reasons.
Sol: Z is a chemical compound, because during the formation of Z, heat is evolved and the properties of Z are different from that of X and Y.
52. Give proper reasons, show that air is a mixture not a chemical compound.
Sol: When we study the characteristics of air, we see that:
(a) Air is a homogeneous, but the proportions of nitrogen, oxygen, carbon dioxide and water vapour are not fixed exactly. The composition of air differs from place to place and from time to time. So, air is a mixture.
(b) The properties of air are not different from those of its constituents. For example, air like oxygen supports combustion, and like carbon dioxide, turns lime water milky. So, air is a mixture.
(c) Various components of air can be separated by a simple process called liquefaction, followed by fractional distillation. So, air is a mixture.
Read More: Matter In Our Surroundings: 35 Ques and Ans
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