Matter – Nature and Behaviour: NCERT Exercise – 2
Question 1. What is meant by a pure substance?
Answer.
A pure substance is a single substance or matter which can not be separated into other kind of matter by any physical process. All elements and compounds are pure substances.
Question 2. Differentiate between homogeneous and heterogeneous mixtures with examples.
Answer.
Homogeneous mixture Heterogeneous mixture
|
1. In it the constituents are uniformly mixed and there are no boundaries of separation. 2. We can not easily see various constituents. 3. We can not easily separate the constituent of such a mixture. We need special methods for separation of constituents of such a mixture. |
1. In it constituents may not be uniformly mixed and there are clear boundaries of separation. 2. We can easily see different constituents. 3. We can easily separate the constituents of such a mixture by ordinary methods of separation of mixtures. |
Examples: Homogeneous mixture: Air, a well mixed solution of vinegar,
Heterogeneous mixture: A mixture of salt and pepper, a mixture of iron fillings and sulphur.
Question 3. How sols, solutions and suspension differ from each other?
Answer.
Difference between sols (i.e. colloidal solutions), solutions (i.e. true solution) and suspension are listed below:
| S.No. | Property | Sol | Solution | Suspension |
| 1. | Nature | Appears to be homogeneous but actually heterogeneous | Homogeneous | Heterogeneous |
| 2. | Particle size | I nm to l00nm | Less than 1 nm | More than 100 nm |
| 3. | visibility | Particles are visible through an ultrrmicro-scope but not with naked eye. | Particles are not
visible even with microscope. |
Particles are visible with naked eye. |
| 4. | Tyndall effect | Light is scattered | No scattering of light | Light is scattered. |
| 5. | Sedimentation | Settle on centrifugation | Do not settle down | May settle due to gravity |
| 6. | Brownian
movement |
Show Brownian
movement |
Do not show
Brownian movement |
May or may not
Show Brownian movement |
Question 4. 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 common salt dissolved (solute) = 36 g Mass of water taken (solvent) = 100 g
Question 5. How will you separate a mixture containing kerosene and petrol (difference in their boiling point is more than 25°C) which are miscible with each other?
Answer.
The components of this mixture can be carried out by process of simple distillation. [Simple distillation process can be used to separate a mixture of miscible liquids in which the difference in boiling point of components is more than 10°C].
Question 6. Name the technique to separate
(i) Butter from curd
Answer (i). Centrifugation
(ii) Salt from sea-water
Answer (ii). Evaporation or crystallization
(iii) Camphor from salt
Answer (iii). Sublimation (camphor is sublime and salt is not sublime substance).
Question 7. What type of mixtures can be separated by technique of crystallization?
Answer.
The technique of crystallization can be used to separate components of a mixture in which one component is less soluble in a particular solvent as compared to the other component, i.e. It makes use of the difference of solubility of substance. It is used to purity substances.
Question 8. Classify the following as a chemical or physical change :
(i) Cutting of trees
Answer (i). Chemical change (It is irreversible)
(ii) Melting of butter in a pan
Answer (ii). Physical change (no new substance formed)
(iii) Rusting of almirah
Answer (iii). Chemical change (rust is oxide of iron)
(iv) Boiling of water to form steam.
Answer (iv). Physical change (no new substance formed)
(v) Passing of electric current through water and the water breaking down into hydrogen and oxygen gases.
Answer (v). Chemical change (Hydrogen and Oxygen are formed).
(vi) Dissolving common salt in water
Answer (vi). Physical change (no new substance formed).
(vii) Making a fruit salad with raw fruits, and .
Answer (vii). Physical change (no new substance formed)
(viii) Burning of paper wood etc.
Answer (viii). Chemical change (It is irreversible)
Question 9. Try segregating the things around you as pure substances or mixtures.
Answer.
We have various substances around us. Here we have classified some of these.
Pure substances: Gold, silver, distilled water, sugar, common salt, diamond, graphite etc.
Mixture: Milk, ice-cream, cold-creams, steel, bronze, vulcanized rubber, curd etc.
Question 10. Which separation techniques will you apply for the separation of the following?
(a) Sodium chloride from its solution in water
Answer (a).
Crystallization: This process is used to separate a pure solid in the form of its crystals from a solution. [Note: This technique is better than evaporation which can also be used to get sodium chloride from its solution in water.]
(b) Ammonium chloride from a mixture containing sodium chloride and ammonium chloride
Answer (b).
Sublimation: Ammonium chloride is a sublime substance and will be collected as sublimate where as sodium chloride is not a sublime substance.
(c) Small pieces of metal in the engine oil of a car
Answer (c).
Filtration: Metal pieces will be collected on filter.
(d) Different pigments from an extract of flower petals
Answer (d).
Chromatography: Pigments are coloured components and they can be separated by chromatographic technique.
(e) Butter from curd
Answer (e).
Centrifugation: On centrifugation butter will get separated.
(f) Oil from water
Answer (f).
Separating funnel: Oil and water are immiscible liquids and can be separated using a separating funnel.
(g) Tea leaves from tea
Answer (g).
Filtration: Tea leaves (solid) will be collected on filter.
(h) Iron pins from sand
Answer (h).
Magnetic separation: Iron pieces are magnetic in nature hence can be separated from sand (non-magnetic) by use of a magnet. Iron gets attracted towards magnet.
(i) Wheat grains from husk.
Answer (i).
Sieving: This method can be used to separate wheat grains from husk.
(j) Fine mud particles suspended in water.
Answer (j).
Sedimentation: During this process mud practices will settle down as precipitate which can then be separated by filtration.