ADDITIONAL QUESTIONS AND ANSWERS:
1. Define (i) solvent. (ii) solute.
Ans: (i) The component of the solution that dissolves the other component in it is called the solvent.(ii) The component of the solution that is dissolved in the solvent is called solute.
2. What is ‘tincture of iodine’.
Ans: A solution of iodine in alcohol is known as tincture of iodine. It has iodine (solid) as the solute and alcohol (liquid) as the solvent.
3. What are alloys.
Ans: The homogeneous mixture of two or more metals or a metal and non-metal is called an alloy. E.g., steel is an alloy of iron and carbon.
4. Give one example of gas in liquid solution.
Ans: Cold-drinks, carbon dioxide gas as solute is mixed with water as a solvent.
5. (a) How can a solution be called dilute or concentrated.
(b) What is “concentration of a solution”.
Ans: (a) The amount of solute dissolving in a solvent decides whether the solution is dilute or concentrated.
(b) The concentration of a solution is the amount of solute present in a given amount of solution or the amount of solute dissolved in a given mass or volume of solvent.
6. State the difference between aqueous and, non-aqueous solution.
Ans: Aqueous solutions have water as solvent and non-aqueous solutions do not have water as solvent.
7. What is “solubility” of a solute.
Ans: The amount of the solute present in the saturated solution at the given temperature is called its solubility.
8. What is (i) saturated solution. (ii) unsaturated solution.
Ans: (i) The maximum amount of solute dissolved in a solvent at given temperature is called saturated solution, where no more solute can dissolve further.
(ii) If the amount of solute contained in a solution is less than the saturation level, it is called an unsaturated solution.
9. How can you convert saturated solution into unsaturated or vice-versa.
Ans: Saturated solution on heating becomes unsaturated and unsaturated solution on cooling becomes saturated.
10. Why water is called universal solvent.
Ans: Water is called universal solvent because it can dissolve large number of substances in it.
11. What is Tyndall effect.
Ans: The scattering of light by colloidal particles is known as Tyndall effect.
12. How can we separate colloidal mixtures.
Ans: By centrifugation, in a centrifuge machine the colloidal solution is kept in a test tube, rotated very fast and due to centrifugal force the colloidal particles are separated.
13. What is (i) emulsion. (ii) aerosol.
Ans: (i)When both the dispersed phase and dispersing medium is liquid, it is called emulsion. eg.,milk, face cream.
(ii) When the solid or liquid is dispersed in a gas it is called aerosol. eg., smoke, fog.
14. What is the principle for separation of immiscible liquids.
Ans: The principle of separating immiscible liquids into layers depending on their densities. The less dense liquid collects at the top and denser liquid at the bottom.
15. What is (i) chromatography. (ii) distillation.
Ans: (i) Chromatography is the technique used for separation of those solutes that dissolve in the same solvent.
(ii) Distillation is the separation technique of two miscible liquids that boils without decomposition and have sufficient difference in their boiling points.
16. How can you separate two liquids that have less than 25 K difference of boiling points.
Ans: To separate a mixture of two or more miscible liquids for which the difference in boiling points is less than 25 K, is fractional distillation.
17. What is (i) condenser (ii) crystallization.
Ans: (i) It is an apparatus used to convert gas into liquid by cooling it.
(ii) When a saturated solution is heated and allowed to cool slowly, crystal of the solute dissolved in the saturated solution are separated from it. It is used to purify solids.
18. Why is mixture called an impure substance.
Ans: Mixture consists of different components which retain their properties and can be easily separated by physical processes, hence it is called as impure substance.
19. State the properties of a solution.
Ans: Properties of a solution are:
(i) A solution is a homogeneous mixture.
(ii) Particles of a solution are smaller than 1 nm and cannot be seen by naked eyes
(iii) They not scatter beam of light.
(iv) The solute particles cannot be separated from the mixture by the process of filtration and thus, the solution is stable
20. Give the differences between mixture and compound.
Ans:
| Mixture | Compound |
| 1. Impure matter 2. Constituents combine in any ratio to form mixture. 3. Constituents retain their properties. 4. Constituents can be separated by physical processes. |
1. Pure matter. 2. Constituents combine in fixed ratio to form a compound. 3. Constituents do not retain their properties as new substance is formed. 4. Constituents cannot be separated by physical processes |
21. Distinguish between a physical change and chemical change.
Ans:
| Physical Change | Chemical Change |
|
1. No new substance is formed. |
1. New substance is formed. 2. It is irreversible change. 3. The properties of constituents are not retained. 4. Completely new substance is formed. |
22. State the properties of a Suspension.
Ans: Properties of a suspension.
(i) Suspension is a heterogeneous mixture having particle size greater than 100 n
(ii) The particles of a suspension can be seen by naked eyes.
(iii) Particles can scatter a beam of light.
(iv) It is unstable.
23. What is a colloidal solution.
Ans: It is a heterogeneous solution which appears to be homogeneous, particles size is very small and so cannot be seen with naked eyes but it is stable. eg. milk and blood.
24. State the properties of colloidal solution.
Ans: Properties of colloidal solution.
(i) It is a heterogeneous mixture having particle size between 1 nm to 100 nm.
(ii) Size of particles is very small, cannot be seen with naked eyes.
(iii) It scatters a beam of light.
(iv) They are stable as the particles do not settle when left undisturbed
25. Give the applications of centrifugation.
Ans: Applications of centrifugation are:
(i) It is used in diagnostic laboratories for blood and urine test.
(ii) It is used in dairies and home to separate butter from cream.
(iii) It is used in a washing machines to squeeze out water from wet clothes
26. Give the applications of chromatography.
Ans: Applications of chromatography are:
(i) To separate colours in a dye.
(ii) To separate pigments from natural colours.
(iii) To separate drugs from blood.
27. Why is crystallization better than evaporation.
Ans: Crystallization is a process that separates a pure solid in the form of its crystals from a solution. Crystallization is better than evaporation because during evaporation some solids decompose or some, like sugar may get charred on heating to dryness. Some impurities may remain dissolved in the solution even after filtration which on evaporation contaminates the solid.
28. How will you separate a mixture of oil and water.
Ans: To separate a mixture of oil and water, we need a separating funnel as both are immiscible liquids. Pour the mixture in separating funnel and let the funnel stand undisturbed for some time. So that separate layer of oil and water are formed. Open the stopcock of the separating funnel and pour out the lower layer of water carefully.
29. A student is given a mixture of naphthalene balls powder and common salt. He needs to separate this mixture. How will he do this. 
Ans: The properties of both naphthalene and common salt should be known, before we choose the separation technique. Naphthalene is a sublimate which on heating changes to gaseous state directly. Hence to separate a volatile compound (sublimate) from a non-volatile compound (non-sublimate), the sublimation process is used.In a China dish the mixture is kept, and is placed on a stand. An inverted funnel is kept over the mixture in China dish with plugged stem. The sublimate on heating gets collected on the funnel and common salt remains in the China dish.
30. How can we obtain different gases from air.
Ans: Air is a homogeneous mixture and its components can be separated by fractional distillation.
31.Write in brief how the water purification system in water works.
Ans: In filtration tank water passes through different layers of sand and gravel as shown in the above figure this is for adsorption of impurities. The clear water reaches a chlorinated tank where water is mixed with bleaching powder/chlorine to kill bacteria and then supplied to houses.
32. Why is air considered as a mixture and not compound.
Ans: Air is considered as a mixture because it shows following properties:
i) Each component present in air retains its properties.
ii) Each component can be separated by simple physical processes. The components do not have any fixed proportion
iii) All gases are present in different amount.
iv) In greener area more oxygen and water vapour is present; near industrial areas the air consists of a lot of impurities and smoke suspended in it.
33. How can you prove that water is a compound.
Ans: Water is a compound because if we pass electricity through it then at two different electrodes, we get two different gases i.e., oxygen and hydrogen during electrolysis of water. The ratio of oxygen: hydrogen is 1: 2 by number of molecules. The properties of oxygen and hydrogen gases sire entirely different from that of liquid water. The ratio of oxygen: hydrogen combination is always constant (1: 2 by volume). To separate the components of water, we need electrolytic cell, and it is not a simple process.
34. What is the difference in fog and smoke.
Ans: Fog is a colloidal solution with liquid dispersed in gas. Smoke is a colloidal solution with solid dispersed in gas.
35. If 20g of salt is present is 220 g of solution, calculate the concentration of solution:
Ans: 
36. Draw a neat diagram of a separating funnel used to separate a mixture of two immiscible liquids, oil and water in the laboratory.
Ans: 
37. Draw a neat diagram to show the separation of constituents of a mixture of ammonium chloride and sand in the laboratory and label it with other parts a) the mixture b) pure ammonium chloride.
Ans: 
ADDITIONAL QUESTIONS: ( Part 2 )
1. Which type of solution is formed when milk and water is mixed uniformly .
Ans :Colloidal solution is formed when milk and water is mixed uniformly .
2. How many elements are known to us till today ?
Ans : 118 elements are known to us till today .
3. Define a solution . Give an example of gas in liquid solution .
Ans : Solution is homogenous mixture of two or more substances . Eg: cold drinks contain carbon dioxide gas dissolved in liquid water
4. What is meant by fractionating column ?
Ans : Fractionating column is a tube packed with glass beads which provide surface for vapour to cool and condense . It gives the effect of repeated distillation .
5. Why the inter conversion of states of matter is considered as a physical change ? Give three reasons to justify your answer .
Ans :
i) It is because it occurs without change in composition .
ii) The substances differs in physical properties but chemically they are same . e.g. water changes into ice below 0° C . Liquid water changes into steam at 100o C . Physical states of water are different due to different force of attraction and intermolecular spaces but composition is same , i.e. all of them contain same water molecules .
iii) No new substance with new properties will form .
6. The ‘sea water’ can be classified as a homogenous as well as heterogeneous mixture
Ans : It is homogenous as salts are dissolved in water . It is heterogeneous due to presence of suspended impurities like mud , rocky particles , decayed plants , etc .
7. i) Define an element . ii) What is meant by malleability . Name any two substances that are malleable .
Ans : i) Elements is a substance which is made up only one kind of atoms .
ii) Malleability is a property due to which a metal can be beaten into sheets . Gold and silver are highly malleable .
8. Why are silicon and germanium metalloids ?
Ans : Silicon and germanium show the properties of both metals as well as non metals , therefore they are called metalloids .
9. Why is sky blue in colour ? Ans: It is due to Tyndall effect . Dust particles and water vapour in air scatter blue light which reaches our eyes and sky looks blue to us .
10. What are heterogeneous mixtures ?
Ans : Those mixture whose composition is not uniform throughout are called heterogeneous .
11. Differentiate between an element and a compound . Write one example of each . (write any two points) .
Ans :
| Element | Compound |
| 1. It consists of one kind of atoms . | 1. It consists of one kind of molecules made up of two or more types of atoms . |
| 2. These are simplest substances and cannot be broken into simpler substances . E.g. Hydrogen | 2. They can broken down into simpler substances . E.g. Water |