3. METALS AND NON – METALS
Questions: 1. Observe the following chemical equations and identify the correct statement.
(i) CuSO4 + Fe → FeSO4 + Cu (ii) 2AgNO3 + Cu → Cu(NO3)2 + 2Ag
(a) Copper is more reactive than Iron and Silver.
(b) Iron is less reactive than Copper and Silver.
(c) Copper is more reactive than Silver but less than Iron.
(d) Silver is more reactive than Copper and Iron. [SSLC July 2018]
Ans: (c) Copper is more reactive than Silver but less than iron.
2. Name a non-metal which is lustrous and a metal which is non-lustrous.
Ans: Non-metal (lustrous) = Iodine (I) Metal (non-lustrous) = Sodium (Na)
3. State two physical properties of gold which are of extreme use to jewellers.
Ans: Malleability, ductility, lustrous (Any two)
4. Write any four physical properties of metals. [SSLC July, 2018]
Ans: (i) Metals are malleable
(ii) Metals have high melting and boiling point.
(iii) Metals are sonorous.
(iv) Metal have shining appearance.
5. The given equation represents the reaction of Copper Sulphate with an element X. CuSO4 + X → Cu + Y Which element is represented by X, among Fe and Ag? Justify your answer. Write the molecular formula of the compound represented by Y. [SSLC April, 2017]
Ans: Fe The reactivity of Fe is more than Cu. FeSO4
6. Draw the diagram of blast furnace used in the extraction of iron. [SSLC April, 2016]
7. Give reason: (i) Sodium metal is stored under kerosene oil.
(ii) Inspite of being highly reactive, aluminium is still used for making utensils.
Ans: (i) Sodium is a highly reactive metal. It can catch fire if kept in open. Hence to protect it and prevent accidental fire, it is stored under kerosene oil.
(ii) Due to high reactivity of aluminium, a thin layer of aluminium oxide is formed on it. This protective layer of aluminium oxide prevents the metal from further corrosion. Hence, aluminium can be used for making utensils. This process is anodizing.
8. Write two observations that you will make when an iron nail is kept in an aqueous solution of copper sulphate. Write the chemical equation for this reaction.
Ans: Blue colour changes to light green. Reddish brown deposit on the iron nail. Fe(s) + CusO4(aq) → FeSO4(aq) + Cu(s)
9. List three properties of sodium by which it differs from the general physical properties of most metals.
Ans: Three properties of sodium are: (i) Sodium is so soft that it can be cut with a knife.
(ii) It has low density.
(iii) It has low melting point.
10. Write one example of each of the following:
(i) Most malleable metal and most ductile metal.
(ii) The best conductor of heat and the poorest conductor of heat.
(iii) A metal with highest melting point and a metal with lowest melting point.
Ans: (i) Gold and silver are most malleable and ductile metal.
(ii) Silver is the best conductor of heat and lead is the poorest conductor of heat.
(iii) Metal with highest melting point—Tungsten, iron. Metal with lowest melting point — Gallium, Caesium.
11. Write the balanced chemical equation for the following reactions:
(i) When copper is heated in air.
(ii) When aluminium is heated in air.
(iii) Aluminium oxide reacts with sodium hydroxide.
Ans: (i) 2Cu + O2 → 2CuO (ii) 4Al + 3O2 → 2Al2O3 (iii) Al2O3 + 2NaOH → 2NaAlO2 + H2O
12. Describe an activity to show that the rusting of iron occurs in the presence of air and moisture.
Ans: (i) Take three test-tubes. Place clean iron nails in each test-tube.
ii) Pour some water in test-tube-i, cork it.
(iii) Pour water (boiled/distilled) in test-tube-2, add some oil and cork it.
(iv) Put some anhydrous calcium chloride in test-tube-3 and cork it.
(v) After 2 – 3 days, we observe that the nails in test-tube 1 rust because they are exposed to air and water both, while nail in test-tube 2 and 3 do not rust. This shows that rusting of iron takes place in the presence of air and moisture both.
13. Compose an activity to arrange Ca, Mg and Fe metals in the decreasing order of reactivity with water. Write suitable balanced chemical equation and draw diagrams.
Ans: Take some metals like Ca, Mg and Fe etc. Place separately small pieces of these metals in beakers with small amount of water in them. If the metals react with the cold water, then the reaction is vigorous. If metal does not react with cold water, then treat it with hot water. Record the observations and arrange the metals in decreasing order of reactivity.
After this activity it can be concluded that Ca is more reactive than Mg, which is more creative than Fe.
14. What is meant by metallurgy?
Ans: The extraction of metals from their ores and then refining them for use is known as metallurgy.
15. Aluminium and zinc do not corrode easily even though they are reactive metals. Give reasons for your answer.
Ans: Aluminium and zinc react with moist air to form a thin protective layer of oxide op their surfaces. This layer prevents further corrosion of the metals.
16. Why is carbon not used for reducing aluminium from aluminium oxide?
Ans: Because aluminium has greater affinity for oxygen than for carbon, therefore carbon cannot reduce alumina (Al2O 3) to aluminium.
17. Draw the diagram of an electrolytic cell used in the purification of copper and label in the purification of copper and label the electrode having impure copper.
Ans:
18. What are ionic compounds? List two properties of these compounds. [SSLC July 2018]
Ans: The compounds which have bonds formed by loss and gain of electrons are called ionic compounds or electrovalent compound and the bond formed is known as ionic bond or electrovalent bond. Two properties of ionic compounds:
(i) Ionic compounds are hard and brittle.
(ii) Ionic compounds have high melting and boiling points.
19. Explain the steps for extraction of copper from its sulphide ore. Write the balanced equations involved in the process.
Ans: (i) 2Cu2S + 3O2 Heat →
2Cu2O(s) + 2SO2(g)
(ii) 2Cu2O + Cu2S Heat →
6Cu(s) + SO2(g)
20. Corrosion is a serious problem. Every year an enormous amount of money is spend to replace damaged iron. What steps can be taken to prevent this damage?
Ans: The rusting of iron can be prevented by painting, oiling, greasing, galvanizing, chrome plating, anodizing or making alloys.
21. Describe electrolytic refining of copper with chemical equations. Draw a well labelled diagram for it. [SSLC July, 2018]
Ans: Electrolytic Refining: This method is widely used as purification of metals like zinc (Zn), copper (Cu), aluminium (Al), chromium (Cr), tin (Sn), lead (Pb), nickel (Ni) and gold (Au). In this process, impure metal is used as anode, a strip of pure metal is used as cathode and soluble salt of metal is used as electrolyte. On passing electric current through the electrolyte, cations move towards cathode, gain electrons and pure metal gets deposited on cathode. In electrolytic refining of copper, the impurities left behind at anode called anode mud contains valuable metals such as gold and silver which can be recovered in the native state.
22. Give reasons for the following: (i) Ionic compounds have high melting point and boiling point. (ii) Ionic compounds conduct electricity in molten state. (iii) Ionic compounds are solids at room temperature and are somewhat hard.
Ans: (i) A large amount of energy is required to break the strong inter-ionic attraction.
(ii) When ionic compounds is present in molten state, crystal structure deforms and they can easily conduct electricity with the mobile ions.
(iii) Due to the strong force of attraction between the positive and negative ions.
23. (a) Observe the following chemical equations: [SSLC April, 2018]
(i) Al2O3 + 2NaOH → 2NaAlO2 + H2O (ii) Al2O3 + 6HCl → 2AlCl3 + 3H2O What is the conclusion that you take about the nature of aluminium oxide with the help of these equations. Give reason for your conclusion.
(b) Molten cryolite is mixed with molten alumina in the extraction of aluminium by electrolysis. Why? Name the substances that are used as anode and cathode in this method.
Ans: (a) Aluminium oxide is amphoteric in nature. Aluminium oxide is reacting with base in the first equation to give salt & water, It is reacting with acid in the second equation to give salt and water. Hence, it is an amphoteric oxide.
(b) (i) Molten cryolite acts as a solvent for alumina forms an electrolyte at low temperature.
(ii) High temperature electrolysis can be avoided, which prevents the loss of aluminium in the form of vapours.
(iii) Anode → Graphite rods (iv) Cathode → Carbon lining.
24. (a) Write the chemical name of the coating that forms on silver and copper articles when these are left exposed to moist air.
(b) Explain what is galvanization. What purpose is served by it?
(c) Define an alloy. How are alloys prepared ? How do the properties of iron change when:
(i) Small quantity of carbon is mixed?
(ii) Nickel and chromium are mixed with it?
Ans: (a) Silver suiphide, copper carbonate coating is formed on Ag & Cu article.
(b) Galvanization is a method of protecting steel and iron from rusting by coating them with a thin layer of zinc. The galvanized article is protected against rusting even if the zinc coating is broken.
(c) Alloy is a homogeneous mixture of two or more metals and non-metals. It is prepared by first melting the primary metal and then dissolving the other elements in it in definite proportion. It is then cooled at room temperature.
(i) On mixing carbons, it becomes hard and strong,
(ii) On mixing Ni and Cr, it becomes hard and does not
25. (i) Name the method used to extract metals of high reactivity.
(ii) Name the main ore of mercury. How is mercury obtained from its ore ? Give balanced chemical equations.
(iii) Explain what is thermite reaction with the help of balanced equation. How is it used to join railway tracks or cracked machine parts?
Ans: (a) Electrolytic reduction. (b) Cinnabar (HgS) By roasting and then self reduction
2HgS + 3O2 Heat →
2HgO + 2SO2,
2HgO Heat →
2Hg + O2 (c) Reaction of Fe2O 3 with Al is used to join railway tracks and machine parts as it is exothermic. This reaction is known as thermite reaction. 1 Fe2O3 + 2Al → 2Fe + Al2O3 + Heat The amount of heat evolved is so large that the metal (Fe) is produced in the molten state.
Textbook Exercises
1. Which of the pairs will give displacement reactions?
(a) NaCl solution and copper metal
(b) MgCl2 solution and aluminium metal
(c) FeSO4 solution and silver metal (d) AgNO3 solution and copper metal
Ans: (d) AgNO3 solution and copper metal.
2. 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
3. An element reacts with oxygen to give a compound with 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
4. Food cans are coated with tin 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) Zin is less reactive than tin
Ans: (c) Zinc is more reactive than tin
5. 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) Assess the usefulness of these tests in distinguishing between metals and non-metals.
Ans: (a) If on hammering, the substance gets break into pieces, then it is a non-metal. But if the substance expands, then it is a metal. Test by passing electric current: Prepare the circuit and place the sample between the clips A and B and switch on the bulb. If the bulb glows than it is metal
(b) Due to malleability, the metals can be hammered into sheet which can be used for various purposes. Since metals are good conductor of electricity, these are used in designing of wire.
6. What are amphoteric oxides? Give two examples of amphoteric oxides.
Ans: Those metal oxides which can react with acids as well as bases to from salt and water are known as amphoteric oxides. Ex: ZnO and Al2O3 ZnO + 2HCl → ZnCl2 + H2O ZnO + 2NaOH → Na2ZnO2 + H2O Al2O3 + 2NaOH → 2 NaAlO2 + H2O Al2O3 + 2NaOH → 2NaAlO3 + H2O
7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not. Ans: Al, Zn will displace and Ag, Au will not displace hydrogen from dilute acids.
8. In the electrolytic refining of a metal M, what would take the anode, the cathode and the electrolyte?
Ans: Anode → Impure metal Cathode → Pure metal Electrolyte → Metal’s salt solution
9. Pratyush took sulphur powder on a spatula and heated it. They 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.
Ans: (a) (i) No change in colour of litmus paper.
(ii) The colour of litmus paper will turn red because sulphur is non-metal and the oxides of non-metal are acidic in nature. (b) S + O2 → SO2 SO2 + HO → H2SO4
10. State two ways to prevent the rusting of iron.
Ans: (i) Coating with Zinc, i.e. galvanisation
(ii) Alloying with Chromium, nickel and titanium
11. What type of oxides are formed when non-metals combine with oxygen?
Ans: Neutral or acidic oxides.
12. 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 ones are usually converted into oxides during the process of extracting.
Ans: (a) It is because, they do not corrode. Hence, do not lose their shine and lustre.
(b) The reaction of these substances with oxygen is highly exothermic. This may cause fire, also they react with water to form base so they are kept in oil.
(c) This is because aluminium is good conductor of heat and electricity. To prevent its reaction with food at high temperature, a protective layer of aluminium oxide (A1203) is formed which prevent further corrosion.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction because it is easier to obtain metal from its oxide as compared with its sulphides or carbonates ore.
13. You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why those sour substances are effective in cleaning the vessel.
Ans: In tarnished copper vessel, there is layer formed due to corrosion which is basic in nature. Lemon or tamarind juice which are acidic in nature cleans the vessels thoroughly.
14. Differentiate between metal and non-metal on the basis of chemical properties.
Ans:
15. 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 had a hasty retreat. Can you play the detective to find out the nature of the solution he had used?
Ans: The solution he had used is Aqua regia. It is a mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3 : 1. Aqua regia has the ability to dissolve the metals like gold and platinum. Since the outer layer of the gold bangles gets dissolved in aqua regia so their weight was reduced drastically.
16. Give reasons why is copper used to make hot water tanks and not steel (an alloy of iron)
Ans: (i) Copper is good conductor of heat than the steel.
(ii) Copper will not be corroded by hot water while the steel may be corroded.
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