3 - Metals and Non-Metals

L - 3, Metals and Non-Metals

PAGE NO - 40




Q1 - Give an example of a metal which
(i) is a liquid at room temperature.
(ii) can be easily cut with knife.
(iii) is the best conductor of heat.
(iv) is a poor conductor of heat.
Ans -
(i) Mercury (Hg)
(ii) Sodium and potassium
(iii) Silver and copper
(iv) Lead and Mercury

Q2 - Explain the meanings of malleable and ductile.
Ans - 
Malleable -  Substance that can b beaten into thin sheets are called malleable. e.g. silver and gold are the best malleable metals.
Ductile -  Substance that can be drawn into thin wires are called ductile. e.g. copper metal used for making electrical wires. 




PAGE NO - 46




Q1 - Why is sodium kept immersed in kerosene oil?
Ans - Sodium is highly reactive metal. When it combine with air or water it catch fire, Therefore, to prevent fire sodium is stored in kerosene oil.

Q2 - Write equations for the reactions of
(i) iron with steam
(ii) calcium and potassium with water
Ans - 
(i) Iron with steam
3Fe (s)  +4H2O (g)  →    Fe2O(aq)  + 4H2

(ii) Calcium and potassium with water. 
Ca (s)  2 H2O (l)   →    Ca(OH)2 (aq)   + H2 (g) + Heat
2K (s)  + 2H2O (l)    →     2KOH (aq)  + H2  +Heat 




Q3 - Samples of four metals A,B, C and D were taken and added to the following solutions one by one. The results obtained have been tabulated as follows.
Use the table above to answer the following questions, about metals A, B, C and D.
*****************************************************
(i) Which is 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 most reactive.
(ii) If B is added to a solutio of copper (II) sulphate then it would displace copper. 
(iii) B > A > C > D is the order of reactivity.




Q4 - Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron’ reacts with dilute H2SO4.
Ans - When a reactive metal reacts with hydrochloric acid hydrogen gas is produced. The equation is as follows :-
           Fe(s) + H2SO4(aq) → FeSO4(aq) + H2(g)




Q5 - What would your observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place.
Ans - Zinc is more reactive than iron, Hence zinc is added a solution or iron (II) sulphate, then it would displace iron form the solution. 




PAGE NO - 49

Q1 - 
(i) Write the electron dot structures for sodium, oxygen and magnesium.
(ii) Show the formation of Na2O and MgO by the transfer of electrons
(iii) What are the ions present in these compounds?
Ans - 
(i) The electron-dot structure of 
*****************************************************
(ii)
************************************
(iii) The ions present in Na2O  are Na+ and O2- ions and in Mgo are Mg2+ and O2- ions.

Q2 - Why do ionic compounds have high melting points?
Ans - Ionic compounds have strong electrostatic forces of attraction between the ions. Which require high energy to overcome these forces. That why ionic compounds have high melting points. 




PAGE NO - 53

Q1 - Define the following terms:
(i) Mineral       
(ii) Ore       
(iii) Gangue
Ans. 
(i) Mineral -  The element or compound which occur naturally in the earth crest are known as minerals. 

(ii) Ore -  The minerals from which metals can be extracted economically on large scale are called ores.

(iii) Gangue - The impurities such as soil and sand present in ore/minerals are called gangue.




Q2 - Name two metals which are found in nature in free state.
Ans - Gold, platinum 




Q3 - What chemical process is used for obtaining a metal from oxide?
Ans - To obtain metals from its oxides for metals of medium reactivity one can use carbon as reducing agent and the chemical process is called reduction. Also; displacement reaction is used in which highly reactive metal acts as reducing agent. !But for the metals of high reactivity the method of electrolytic reduction in used.
         e.g., 3MnO(s) + 4Al (s) → 3Mn (l) + 2Al2O(s) + heat




PAGE NO - 55

Q1 - Metallic oxides of zinc, magnesium and copper were heated with the following metals.
     ***********************************    
In which cases will you find displacement reactions take place?
Ans - *************************************
         
Q2 - Which metals do not corrode easily?
Ans - Metals which are less reactive and lie at the bottom of reactivity series i.e., silver, gold, platinum do not react with atmospheric gases and hence do not corrode easily.




Q3 - What are alloys?
Ans - Alloys are homogeneous mixture of two or more metals or metals or metal and non-metal.

EXCERSISE

Q1 - Which of the following pairs will give displacement reactions?
(a) NaCl solution and copper metal 
(b) MgCI2 solution and aluminium metal
(c) FeSO4 solution and silver metal 
(d) AgNO3 solution and copper metal
Ans - 
(d) AgNO3 solution and copper metal




Q2 - 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




Q3 - An element reacts with oxygen to giver a compound with a high melting point. This compound is also soluble in water. This element is likely to be
(a) calcium            
(b) carbon            
(c) silicon            
(d) iron
Ans - (a) Calcium.




Q4 - Food cans are coated with tin and not with zinc because
(a) zinc is costlier then tin.                        
(b) zinc has 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.




Q5 - You are given a hammer, a battery, a bulb, wires and 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) To distinguish between samples-of- metals and non-metals one can use hammer to beat the given material into sheets, if it breaks it is non-metal but if it is beaten into thin sheets it is a metal.
           One can also use battery, wires, bulb and switch to make a circuit and use the given material to complete the circuit one by one, if the electric current flows and the bulb glows then it is metal and if not then it is non-metal.
(b) Though these tests gives us rough ideas in distinguishing between metals and non-metals but they are not reliable because both in metals & non-metals there are exceptions. For example Na metal is brittle and graphite can show conductivity.




Q6 - What are amphoteric oxides? Give two examples of amphoteric oxides.
Ans - Those oxides that behave as both acidic and basic oxides are called amphoteric oxides.
 Ex -  Al2O3 and ZnO




Q7 - Name two metals which will displace hydrogen from dilute acids and two metals which will not.
Ans - Metals which are more reactive than hydrogen displace it form dilute acids.
Ex - Sodium and potassium 
Metals that are less reactive than hydrogen do not displace it. 
Ex - Copper and silver 

Q8 - In the electrolytic refining of M, what would you take as the anode, the cathode and the electrolyte?
Ans - For electrolytic refining of M:
           Impure metal M → at anode
           Pure sample of M → at cathode
           Electrolyte → soluble salt of metal M
Q9 - 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 the balanced chemical equation for the reaction taking place.
Ans - 
(a) 
     (i) There will be no effect of gas on dry litmus paper.
     (ii) Moist blue litmus paper turns red.
(b) 
(i) S (s) + O2 (g)→ SO(s)                
(ii) SO2 (g) + H2O (l) → H2SO3(aq)




Q10 - State two ways to prevent the rusting of iron.
Ans - 
(i) Rusting can be prevented by painting iron articles so that iron surface does not come in contact with air and moisture required for rusting.
(ii) By coating iron articles with a protective layer of zinc metal by galvanization which prevents the rusting of iron.

Q11 - What type of oxides are formed when non-metals combine with oxygen?
Ans - When non-metals combine with oxygen they form acidic oxides.
Ex - S (s)  + O2 (g)    →     SO2 (g)




Q12 - Give reasons:
(a) Platinum, gold and silver are used to make jewellery.
(b) Sodium, potassium and lithium are stored under oil.
(c) Aluminium is highly reactive metal, yet it Is used to make utensils for coking.
(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
Ans - 
(a) Platinum, gold, and silver are used to make jewellery because they are very lustrous, they also less reactive and shiny. 
(b) Reaction of sodium, potassium and lithium with oxygen is so exothermic that they catch fire. To prevent fire they are stored in kerosene oil. 
(c) This is because aluminium is good conductor of heat aluminium forms a layer of aluminium oxide at high temperature which is prevent the further corrosion.
(d) Because it is easy to reduce oxide than the carbonates and sulphide to the metals.
Q13 - You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessel?
Ans - Copper metal corrodes to form copper carbonate and get tarnished. On cleaning with lemon or tamarind juice, the acid present in: them dissolves the copper carbonate thereby cleaning the vessel.




14 - Differentiate between metal and non-metal on the basis of their chemical properties.
Ans -
Metal
Non-metal
1. They react with water
They do not react with water
2. Metals foam basic oxides.
Nonmetals form acidic oxides.
3. Metals can displace hydrogen from acids.
Non-metals cannot displace hydrogen from acids.
4. Metals displaces hydrogen from water
Non-metals do not displaces hydrogen form water




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?
Ans - The solution is aqua regia (It cantain 1:3 conc. HNO3 acid : conc. HCl acid) is used by the goldsmith, which dissolves the upper layer of gold in it, and the inner shiny layer appears. Due to this gold also loose their weight.

16 - Give reason why copper is used to make hot water tanks and not steel (an alloy of iron).
Ans - Copper do not react with hot water, cold water and steam. It is also good conductor of heat. 
And 
Steel is the alloy of iron it would react vigorously with the steam formed form hot water


Post a Comment

7 Comments