3 Metals and Non-Metals

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1 3 Intext Questions On Page 40 Question 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. (i) Mercury (ii) Sodium (iii) Silver (iv) Lead Question 2. Explain the meanings of malleable and ductile. Malleable Metals have a property that they can be beaten into thin sheets by hammering. Such metals are called malleable. Ductile Metals which can be drawn into thin wires are called ductile metals. On Page 46 Question 1. Why is sodium kept immersed in kerosene oil? Sodium is a very reactive metal. It reacts with air and water vigorously at room temperature. So, it is kept immersed in kerosene to prevent its exposure to air/water. Question 2. Write equations for the reaction of (i) iron with steam (ii) calcium with water (iii) Potassium with water steam (i) 3Fe() s + 4H O() g Fe O () s + 4H () g (ii) Ca() s + 2H2O ( l) Ca(OH) 2( aq) + H2() g (iii) 2K ( s) + 2H2O () l 2KOH( aq) + H2 ( g) Question 3. 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. Metal 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 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?

2 (iii) Arrange the metals A, B, C and D in the order of decreasing reactivity. Based on the activity series, the relative position, of metals present in the question is Zn> Fe> Cu> Ag. On the basis of results shown in the table we can say (i) B is the most reactive because it displaces Fe. (ii) Cu will be displaced because B is more reactive than Fe so it is also more reactive than Cu. (iii) B > A> C > D. Question 4. Which gas is produced when dilute hydrochloric acid (HCl) is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4 2Na + 2dil HCl 2NaCl + H 2 Hydrogen gas is released. Fe() s + H SO FeSO + H () g Question 5. What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place. When Zn reacts with FeSO 4, the pale green colour of the solution changes to colourless because Zn being more reactive than Fe, will displace it. Fine grey particles of Fe are also seen. Zn + FeSO ZnSO + Fe On Page (Pale green) Colourless Grey Question 1. (i) Write the electron-dot structures for sodium, oxygen and magnesium. (ii) Show the formation of Na 2 O and MgO by the transfer of electrons. (iii) What are the ions present in these compounds? (i) Sodium (Na) Atomic number = 11 Electronic configuration Electron dot structure (a) Oxygen (O) Atomic number = 8 Electronic configuration 2 8 1,, K L M Na 2 6 K, L Electron dot structure O (b) Magnesium (Mg) Atomic number = 12

3 Electronic configuration Electorn dot structure (ii) Formation of Na O ,, K L M Mg Na + Na O + Na Na Sodium + Oxygen Sodium ion Formation of MgO : O 2 Na O Oxygen Sodium oxide ion 2+ Mg O [ Mg] O Magnesium Magnesium Oxygen Oxygen ion (iii) Na 2 O contains Na + and O 2 ions. MgO contains Mg 2+ and O 2 ions. Question MgO Magnesium oxide Why do ionic compounds have high melting points? Ionic compounds have high melting points because a considerable amount of energy is required to break the strong inter-ionic attraction existing in ionic compounds. On Page 53 Question 1. Define the following terms. (i) Mineral (ii) Ore (iii) Gangue (i) Minerals The elements or compounds in the form of which metal occur naturally in the earths crust are called minerals. (ii) Ores Those minerals from which metals can be profitably extracted are called ores. (iii) Gangue The various impurities like sand, dust, rocky particles that are associated with the ore are called gangue/matrix. Question 2. Name two metals which are found in nature in the free state. Gold and silver are found in nature in free state because they are unreactive and inert. Question 3. What chemical process is used for obtaining a metal from its oxide? Reduction method is used to obtain a metal from its oxide, e.g., MO + C CO + M (where M = metal)

4 On Page 55 Question 1. 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? Metal Zn Mg Cu ZnO Displacement No displacement MgO No displacement No displacement CuO Displacement Displacement [Because Mg > Zn > Cu (Reactivity order)] Question 2. Which metals do not corrode easily? Gold and platinum as these are inert metals. Question 3. What are alloys? An alloy is a homogeneous mixture of two or more metals or a metal and a non-metal having a uniform composition. Exercises Question 1. Which of the following pairs will give displacement reactions? (a) NaCl solution and copper metal (b) MgCl 2 solution and aluminium metal (c) FeSO 4 solution and silver metal (d) AgNO 3 solution and copper metal (d) AgNO 3 solution will give displacement reaction with copper (Cu) because copper is placed above silver in the activity series. i.e., copper is more reactive than silver. 2AgNO + Cu Cu( NO ) + 2Ag Question 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 these (d) All the given methods are helpful in preventing an iron frypan from rusting.

5 Question 3. 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 (a) The compound is likely to be of calcium (Ca) because it combines with oxygen to give CaO (calcium oxide) with very high melting point. Calcium oxide dissolves in water to from calcium hydroxide. 2Ca + O2 2CaO CaO + H2O 2Ca(O H) 2 Calcium hydroxide Question 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) zinc is less reactive than tin (c) Food cans are not coated with zinc because it being more reactive than tin, it can react with organic acids present in the food. Question 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. (a) (i) Take the given samples, hammer them and observe. If the given sample breaks easily then it is a non-metal but if it doesn t then it is a metal. (ii) If on hammering a sound is heard then it is a metal (metals are sonorous). If no sound is produced on hammering then the sample is a non-metal. (iii) Now create a circuit using a battery, a bulb, wires and a switch (as shown in the figure). Battery Bulb Clips Switch A B Insert sample to be tested Insert any one sample between clips A and B. If the bulb glows it indicates that the sample is a good conductor of electricity and hence it is a metal. If the sample doesn t light the bulb then it is non-metal. (b) From the above tests it is clear that metals are sonorous, malleable and good conductors of electricity whereas non-metals are non-sonorous, non-malleable and poor conductors of electricity.

6 Question 6. What are amphoteric oxides? Give two examples of amphoteric oxides. Some metal oxides, such as aluminium oxide, zinc oxide etc., show the properties of acids as well as bases, i.e., they react with acids and bases both to produce salts and water. These are called amphoteric oxides. eg.., Al2O 3 + 6HCl 2AlCl 3 + 3H2O Al2O 3 + 2NaOH 2NaAlO2 + H2O Question 7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not. Metals which displace hydrogen from dilute acids are Mg and Al, because these metals exist at higher position in activity series. 61 Metals which will not displace hydrogen from dilute acids are Cu and Ag because these metals exist at lower position in activity series. Question 8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte? Anode Crude (Impure) metal M Cathode Thin strip of pure metal M Electrolyte Some salt of metal M In electrolytic refining, the impure metal is converted into a block which is made anode in an electrolytic cell in which a plate of pure metal acts as the cathode. The electrolyte is the solution of the soluble salt of the same metal, preferably a double salt. On passing electric current, metal ions from the electrolyte are reduced to the metal which is deposited on the cathode. An equivalent amount of the pure metal from the anode gets oxidised and the metal ions (or cations) go into the solution. This keeps on till the whole of the metal from the anode dissolves and deposits on cathode, leaving behind impurities in the form of a mud below anode called the anode mud. Question 9. 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. Test tube Spatula containing sulphur powder Burner Collection of gas (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 Metals taking and place. Non-Metals (a) The gas collected is sulphur dioxide (SO 2 ), An acidic gas. So,

7 Collection of gas (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. (a) The gas collected is sulphur dioxide (SO 2 ), An acidic gas. So, (i) it will have no action on dry litmus. (ii) the gas will have bleaching action on moist litmus paper. 62(b) Balanced equation is + 2 SO ( g) + H O () l H SO ( aq) 2H ( aq) + SO ( aq) Question 10. State two ways to prevent the rusting of iron. Ways to prevent rusting of iron (i) By painting or greasing the surface of iron, it can be prevented from rusting because in this condition iron will not be in the direct contact with air. (ii) By galvanising the iron surface. In glavanisation a layer of zinc is coated on the iron surface. Zinc is more reactive than iron, so it will be rusted in preference of iron. Question 11. What type of oxides are formed when non-metals combine with oxygen? Non-metals combine with O 2 to form Acidic oxide e.g., CO 2 and SO 2 Neutral oxides e.g., NO,HO 2 2 Question 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 ores are usually converted into oxides during the process of extraction. (a) Platinum, gold and silver are most ductile, malleable and lustrous metals. These metals have little affinity for oxygen and thus are not attacked by moist air hence they are suitable for making jewellery. (b) Sodium, potassium and lithium are very reactive metals and react vigorously with air and water. They can even catch fire if kept in open air. So, they are stored under oil. (c) Al is a good conductor of heat and is resistant to corrosion (This is because it reacts with air to form a thin oxide layer Al 2 O 3 which is very stable and prevents further corrosion). It is also very light weight and malleable. Hence, it is used for making utensils. (d) Because it is easier to obtain a metal from its oxide as compared to its sulphides and carbonates. Question 13. 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. CO 2 in air reacts with copper articles and tarnishes it. Copper slowly loses its shine and forms a green coating on its surface due to the formation of basic copper carbonate (green). 3

8 Question 13. 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. CO 2 in air reacts with copper articles and tarnishes it. Copper slowly loses its shine and forms a green coating on its surface due to the formation of basic copper carbonate (green). 2Cu + H O + CO + O CuCO Cu(OH) Air Basic copper carbonate This is insoluble in water. So, copper vessels cannot be cleaned with water. Lemon juice contains citric acid while tartaric acid exists in tamarind. These acids react with basic copper carbonate to form soluble salts. These salts are removed from the surface of copper metal and the metal shines. Question 14. Differentiate between metal and non-metal on the basis of their chemical properties. Metal Non-Metal 1. Metals are electropositive in nature. Non-metals are electronegative in nature. M M + +e e NM + NM 2. Metals form basic oxides Non-metals form acidic/neutral oxides. e.g., 2Mg + O 2 2MgO e.g., C + O 2 CO 2 (Acidic oxide) 3. Metals replace hydrogen from dil. acids Non-metals do not replace hydrogen M + dil. HCl MCl + from dil. acids. H 2 4. Metals react with water to form metal oxide/metal hydroxide and hydrogen gas. Non-metals do not react with water/steam to evolve H 2 as they can t give electrons to hydrogen ions of water. Question 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 beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used? The man used aqua-regia. A mixture of conc. HCl and conc. HNO 3 in the ratio of 3 : 1. This mixture can dissolve gold. Neither conc. HCl nor con. HNO 3 can do this alone. It is highly corrosive and since it can dissolve gold therefore the weight of bangles reduced drastically. Question 16. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).

9 Reasons 1. Copper is one of the best conductors of heat. 2. Copper does not react with boiling water/steam whereas steel reacts with steam. 3. Copper has a higher melting point as compared to steel.