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EDUCATIONAL SERVICES 12-A2, Yusuf Sarai N.D. 16 Ph. 65643449

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Ans. Sodium is kept immersed in kerosene oil as it reacts vigorously with Ans. (i) 3Fe (s) + 4H2O (g) ? Fe3O4 (s) + 4H2 (g) (ii) (a) Ca (s) + 2H2O ? Ca

     EDUCATIONAL SERVICES

    12-A/2, Yusuf Sarai N.D. 16 Ph.: 65643449, 9810004225

     www.eeducationalservices.com

     Chapter 3

     Metals and Non- metals

Q 1. Give an example of a metal which

     (i) is a liquid at room temperature. (ii) can be easily cut with a knife. (iii) is the best conductor of heat.

     (iv) is a poor conductor of heat.

    Ans. (i) Mercury is liquid at room temperature. (ii) Sodium can be easily cut by a knife. (iii) Silver is the best conductor of

     heat. (iv) Lead is the poorest conductor of heat.

    Q 2. Explain the meanings of malleable and ductile.

    Ans. When a metal can be beaten in to thin sheets with a hammer, the metal is called malleable and the property is called

     malleability. When a metal can be drawn in to thin wires, the metal is called ductile and the property is called ductility. Q 3. Why is sodium kept immersed in kerosene oil?

    Ans. Sodium is kept immersed in kerosene oil as it reacts vigorously with air to catch fire.

    Q 4. Write equations for the reactions of

     (i) iron with steam (ii) calcium and potassium with water.

    (l)Ans. (i) 3Fe (s) + 4HO (g) ? FeO (s) + 4H (g) (ii) (a) Ca (s) + 2HO ? Ca (OH) (aq) + H(g) 2342222

    (l) (iii) 2K (s) + 2HO? 2KOH (aq) + H (g) + Heat energy 22Q 5. Samples of four metals A, B, C and D were taken and added to the following solution one by one. The results obtained

     have been tabulated as follows:

     Metals Iron (II) sulphate Copper (II) sulphate Zinc sulphate Silver nitrate

     A No reaction Displacement ? ?

     B Displacement No reaction ? ? C No reaction No reaction No reaction Displacement

     D No reaction No reaction No reaction No reaction

     Use the table given above to answer the following questions about metals A, B, C and D.

     (i) Which is the most reactive metal? (ii) What would you observe if B is added to a solution of copper (II) sulphate?

     (iii) Arrange the metals A, B, C and D in the order of decreasing reactivity.

    Ans. (i) B is the most reactive metal.

     (ii) When B is added to the solution of copper(II) sulphate, the blue colour of copper sulphate solution will fade a

     colourless solution of B sulphate (zinc sulphate) would be obtained. One would also observe that red - brown particles

     of copper settles at the bottom of the container.

     (iii) B ? A ?C ? D or Zn ? Pb ? Cu ? Ag.

    Q 6. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron

     reacts with dilute sulphuric acid (HSO). 24

    Ans. When dilute hydrochloric acid is added to a reactive metal, hydrogen gas is evolved.

     Metal + dilute hydrochloric acid ? Metal salt + Hydrogen

     Reaction of iron with dilute sulphuric acid: Fe (s) + HSO (aq) ? FeSO (aq) + H (g) 2442 Sulphuric acid Ferrous sulphate

Q 7. What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes

     place.

    Ans. When zinc is added to a solution of iron (II) sulphate green colour of iron (II) sulphate fades out. The colourless solution

     of zinc sulphate is formed and iron metal is deposited on zinc.

     Reaction : Zn (s) + FeSO(aq) ? ZnSO(aq) + Fe (s) 44

Q 8. (i) Write the electron- dot structures for sodium, oxygen and magnesium. O and MgO by the transfer of electrons. 2 (ii) Show the formation of Na (iii) What are the ions present in these compounds

    Ans. (i) Electron dot structures of sodium, oxygen and magnesium

     +2? (iii) (a) Sodium ions (2Na) and oxide ion (O) are present in the compound NaO. 22+ 2? (b) Magnesium ion (Mg) and oxide ion (O ) are present in the compound MgO.

    Q 9. Why do ionic compounds have high melting points.?

    Ans. Why do ionic compounds have high melting point. This is because considerable amount of energy is required to break

     the strong inter ionic attraction.

    Q10. Define the following terms: (i) mineral (ii) ore and (iii) gangue. Ans. (i) The naturally occurring compounds of metals which are generally mixed with other matter such as soil, sand, limestone

     and rocks are called minerals.

     (ii) These minerals from which the metals are extracted commercially at a comparatively low cost and with minimum

     effort are called ores.

     (iii) The impurity of sand and rocky minerals present in the ore is called gangue.

    Q11. Name two metals which are found in nature in the free state.

    Ans. Gold and copper.

    Q12. What chemical process is used for obtaining a metal from its oxide?

    Ans. A chemical process called reduction is used for obtaining a metal from its oxide. Sometimes displacement reactions can

     also be used. The highly reactive metals such as sodium, calcium, aluminium etc, are used as reducing agents because they

     can displace metals of lower reactivity from their compounds.

    Q13. Metallic oxides of zinc, magnesium and copper were heated with the following metals.

     Metal Zinc Magnesium Copper

    Zinc oxide ? ? ?

    Magnesium oxide ? ? ? Copper oxide ? ? ? In which cases will you find displacement reactions taking place?

    Ans.

    Metal Zinc Magnesium Copper

    Zinc oxide Displacement ? ?

    Magnesium oxide ? ? ? Copper oxide Displacement Displacement ?

Q14. Which metals do not corrode easily ?

    Ans. Metals which are placed below in activity series like silver, gold and platinum do not corrode easily.

    Q15. What are alloys?

    Ans. An alloy is a homogeneous mixture of two or more metals or a non- metal. It is prepared by first melting the primary

     metal, and then dissolving the other elements in it in definite proportions. It is then cooled to room temperature.

    Q16. Which of the following pairs will give displacement reactions?

     (a) NaCl solution and copper metal (b) MgCl solution and aluminium metal. 2

     (c) FeSO solution and silver metal (d) AgNO solution and copper metal. 43Ans. (d) [ Hint : A metal above in activity series can displace the metal lower in series from its salt solution.]

    Q17. Which of the following methods is suitable for preventing an iron frying pan from rusting?

     (a) Applying grease (b) Applying paint (c) Applying a coating of zinc (d) All of the above Ans. (c) Applying a coating of zinc.

Q18. An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water.

     The element is likely to be

     (a) Calcium (b) Carbon (c) Silicon (d) Iron

    Ans. (a) Calcium.

    Q19. Food cans are coated with thin and not with zinc because

     (a) zinc is costlier than tin (b) zinc has a higher melting point than tin. (c) zinc is more reactive than tin.

     (d) zinc is less reactive than tin.

    Ans. (c) Zinc is more reactive than tin.

    Q20. You are given a hammer, a battery, a bulb, wires and a switch.

     (a) How could you use them to distinguish between samples of metals and non-metals ?

     (b) Asses the usefulness of these tests in distinguishing between metals and non- metals?

    Ans. (a) (i) On hammering the metals and non- metals, metals would give thin sheets whereas non-metal will break down in to

     pieces.

     (ii) By using a bulb, a battery, wires and a switch etc, given an arrangement of the type shown in figure, will be made.

     When the sample of metals and non-metals is inserted one by one between the clips and switch is made on. The

     bulb will glow when the metal is inserted, whereas bulb will not glow in case of non-metal.

(b) The method a (ii) seems

    to be authentic to make a

    difference between metals

    and non-metals.

    Q21. What are amphoteric

    oxides? Give two examples of amphoteric oxides.

    Ans. Those oxides which react with both acids as well as bases to produce salt and water are known as amphoteric oxides. O) and zinc oxide (ZnO). 23 Two examples of amphoteric oxides are: Aluminium oxide (AlQ22. Name two metals which will displace hydrogen from dilute acids, and two metals which will not?

    Ans. Magnesium and zinc would displace hydrogen from dilute acids whereas copper and silver will not displace hydrogen

     from dilute acids.

    Q23. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?

    Ans. In electrolytic refining of a metal M, the impure metal M is made the anode and a thin strip of pure metal M is made the

     cathode. A solution of the metal M salt is used as an electrolyte.

     Examples: For refining copper metal, anode and cathode will be made of copper and electrolyte would be acidified copper

     sulphate solution. Of course, the strip of the pure metal would be made cathode, and that of impure metal

     would be made anode.

Q24. Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it as

     shown in figure. below.

     (a) What will be the action of gas on

     (i) dry litmus paper? (ii) moist litmus paper?

     (b) Write a balanced chemical equation for the reaction taking place.

     Fig. 3.2 Collection of gas

    Ans. (a) (i) There will be no effect on dry litmus paper. (ii) There will be effect on moist litmus paper. It becomes red.

     (g) ? SO (g) (b) Balanced equation for the above reaction: S (s) + O22 Sulphur dioxide

Q25. State two ways to prevent the rusting of iron.

    Ans. Rusting of iron can be prevented by painting, oiling, greasing, galvanising, chrome painting, anodising or making alloys.

    Q26. What types of oxides are formed when non-metals combine with oxygen?

    Ans. Acidic oxides are formed when non-metals combine with oxygen.

Q27. Give reasons: (a) Platinum, gold and silver are used to make jewellery. (b) Sodium, potassium and lithium are stored

     under oil. (c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking. (d) Carbonate and sulphide

     ores are usually converted in to oxides during the process of extraction.

    Ans. (a) Because these metals do not react with SO, CO and HS gas present in the air and hence their glow is retained. 222

     (b) Sodium, potassium and lithium are stored under oil because they vigorously react with oxygen of the air and even

     catch fire.

     (c) Yes. aluminium is a reactive metal still it is being used to make utensils for cooking, this is because aluminium forms a

     layer of aluminium oxide which resist in spoiling any food material.

     (d) Carbonate and sulphate ores are usually converted in to oxides during the process of extraction because it is easier to

     obtain a metal from its oxide as compared to its carbonates and sulphides.

    Q28. You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain, why these sour

     substances are effective in cleaning the vessels.

    Ans. Yes, when copper vessel is kept in most air then it reacts with moist carbon dioxide in the air to form a green substance.

     The green substance is copper carbonate, which is basic in nature. When it is treated with lemon or tamarind juice

     containing acid neutralisation of base occurs which cleans the vessel.

    Q29. Differentiate between metal and non-metal on the basis of their chemical properties.

    Ans. Difference between metal and non-metals on the basis of chemical properties:

     Metals Non-metals

     (1) Metals form basic oxides. (1) Non-metals form acidic oxides or neutral oxides.

     (2) Metals displace hydrogen from water (or steam) (2) Non-metals do not react with water (or steam) and hence

     (3) Metals displace hydrogen from dilute acids. do not displace hydrogen from water (or steam).

     (4) Metals form ionic chlorides with chlorine. These (3) Non-metals do not react with dilute acids and hence do

     ionic chlorides are electrolytes but non-volatile. not displace hydrogen from dilute acids. (5) Metals usually do not combine with hydrogen. Only a (4) Non-metals form covalent chlorides with chlorine

     few reactive metals combine with hydrogen to form (which are non-electrolytes but volatile).

     ionic metal hydrides. (5) Non-metals react with hydrogen to form stable, covalent

     hydrides.

    Q30. A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An

     unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like

     new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat.

     Can you play the detective to find out the nature of the solution he had used?

    Ans. The man posing as goldsmith used aqua regia a mixture of 3:1 concentrated hydrochloric and concentrated nitric acid.

     When any gold ornament is dipped in this mixture the gold dissolves.

    Q31. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).

    Ans. Copper is used to make hot water tanks because copper is a very good conductor of heat and electricity, whereas steel (an

     alloy of iron) is not a good conductor of heat and electricity.

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