Monday, 5 December 2011

CBSE Class 10th Science | Chapter 3. Metals and Non-metals | Solved Exercises

Points to Remember - What you have learnt

  1. Elements can be classified as metals and non-metals.
  2. Metals are lustrous, malleable, ductile and are good conductors of heat and electricity. They are solids at room temperature, except mercury which is a liquid.
  3. Let us learn more about the properties of Metals
    1. Metals, in their pure state, have a shining surface. This property is called metallic lustre.
    2. The metals are generally hard. The hardness varies from metal to metal.
    3. Some metals can be beaten into thin sheets. This property is called malleability. Did you know that gold and silver are the most malleable metals?
    4. The ability of metals to be drawn into thin wires is called ductility. Gold is the most ductile metal
    5. The metals are good conductors of heat and have high melting points. The best conductors of heat are silver and copper. Lead and mercury are comparatively poor conductors of heat.
    6. The metals are good conductors of Electricity
  4. Metals can form positive ions by losing electrons to non-metals.
  5. Metals combine with oxygen to form basic oxides. Aluminium oxide and zinc oxide show the properties of both basic as well as acidic oxides. These oxides are known
    as amphoteric oxides.
  6. Different metals have different reactivities with water and dilute acids.
  7. A list of common metals arranged in order of their decreasing reactivity is known as an activity series.
  8. Metals above hydrogen in the Activity series can displace hydrogen from dilute acids.
  9. A more reactive metal displaces a less reactive metal from its salt solution.
  10. Metals occur in nature as free elements or in the form of their compounds.
  11. The extraction of metals from their ores and then refining them for use is known as metallurgy.
  12. An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.
  13. The surface of some metals, such as iron, is corroded when they are exposed to moist air for a long period of time. This phenomenon is known as corrosion.
  14. Non-metals have properties opposite to that of metals. They are neither malleable nor ductile. They are bad conductors of heat and electricity, except for graphite,
    which conducts electricity.
  15. Non-metals form negatively charged ions by gaining electrons when reacting with metals.
  16. Non-metals form oxides which are either acidic or neutral.
  17. Non-metals do not displace hydrogen from dilute acids. They react with hydrogen to form hydrides.

Activity 3.1 Page No. 37

  • Take samples of iron, copper, aluminium and magnesium. Note the appearance of each sample.
  • Answer: They have a shining surface.
  • Clean the surface of each sample by rubbing them with sand paper and note their appearance again.
  • Answer: They become more shiny.

Activity 3.2 Page No. 37

  • Take small pieces of iron, copper, aluminium, and magnesium.Try to cut these metals with a sharp knife and note your observations.
  • Answer:They are very hard to cut.
  • Hold a piece of sodium metal with a pair of tongs.
    CAUTION: Always handle sodium metal with care. Dry it by pressing between the folds of a filter paper.
  • Put it on a watch-glass and try to cut it with a knife.
  • What do you observe?
  • Answer: Sodium can be cut easily with knife.

Activity 3.3 Page No. 38

  • Take pieces of iron, zinc, lead and copper.
  • Place any one metal on a block of iron and strike it four or five times with a hammer. What do you observe?
  • Repeat with other metals.
  • Record the change in the shape of these metals.
  • Answer: The metals take the form of sheets on beating.

Activity 3.4 Page No. 38

  • Consider some metals such as iron, copper, aluminium, lead, etc.
  • Which of the above metals are also available in the form of wires?
  • Answer: Iron, copper and aluminium..

Activity 3.5 Page No. 39


-
  • Take an aluminium or copper wire. Clamp this wire on a stand, as shown in Figure.
  • Fix a pin to the free end of the wire using wax.
  • Heat the wire with a spirit lamp, candle or a burner near the place where it is clamped.
  • What do you observe after some time?
  • Answer. After some time the wax melts and the pin falls down.
  • Note your observations. Does the metal wire melt?
  • Answer. No, the metal wire does not melt.


Activity 3.6 Page No 39


  • Set up an electric circuit as shown in Figure?
  • Place the metal to be tested in the circuit between terminals A and B as shown.
  • Does the bulb glow? What does this indicate?
  • Answer. Yes, the bulb glow. This indicate that metal inserted between terminals A and B, is a conductor of electricity

Activity 3.7

  • Collect samples of carbon (coal or graphite), sulphur and iodine.
  • Carry out the Activities 3.1 to 3.6 with these non-metals and record your observations.
ElementSymbolType of SurfaceHardnessMalleabilityDuctilityConduction
Heat Electrcity
Sonority
Carbon (Coal)Croughmoderatenot malleablenot ductile
 No       No     
No
SulphurSroughnot hardnot malleablenot ductile
   No      No    
No
IodineIshinynot hardnot malleablenot ductile
  No        No   
 No

Activity 3.8 Page No 49

  • Take a magnesium ribbon and some sulphur powder.
  • Burn the magnesium ribbon. Collect the ashes formed and dissolve them in water.
  • Test the resultant solution with both red and blue litmus paper.
  • Is the product formed on burning magnesium acidic or basic?
  • Answer. Basic
  • Now burn sulphur powder. Place a test tube over the burning
  • sulphur to collect the fumes produced.
  • Add some water to the above test tube and shake.
  • Test this solution with blue and red litmus paper.
  • Is the product formed on burning sulphur acidic or basic?
  • Answer. Acidic
  • Can you write equations for these reactions?
  • Answer.
    2Mg + O2 = 2Mgo
    Mgo + H2O = Mg(oH)2
    S + O2 = SO2
    SO2 + H2O = H2SO4
  • Intext Question : 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. Answer. (i) Mercury is a liquid at room temperature. (ii) Sodium can be easily cut with a knife. (iii) Silver is the best conductor of heat. (iv) Astatine is a poor conductor of heat. In fact Astatine is the poorest conductor of heat among all metals. Its conductivity is less than even some non-metals like graphite. Question 2. Explain the meanings of malleable and ductile. Answer. MalleableSome metals can be beaten into thin sheets. This property is called malleability. Ductile The ability of metals to be drawn into thin wires is called ductility. Gold is the most ductile metal

    Activity 3.9 Page No. 41

    CAUTION: The following activity needs the teacher’s assistance. It would be better if students wear eye protection.
    • Hold any of the samples taken above with a pair of tongs and try burning over a flame. Repeat with the other metal samples.
    • Collect the product if formed.
    • Let the products and the metal surface cool down.
    • Which metals burn easily?
    • Answer. Magnesium
    • What flame colour did you observe when the metal burnt?
    • Answer. Blue
    • How does the metal surface appear after burning?
    • Answer. Silver white.
    • Arrange the metals in the decreasing order of their reactivity towards oxygen.
    • Answer. Na > Mg > Al > Zn > Fe > Pb > Copper
    • Are the products soluble in water?
    • Answer. . Oxides of Alumium,Copper, Iron, Lead, Mg, Zn  are not  Soluble. Soudium Oxide is soluble in water
    • Activity 3.10 Page No. 42

       

      CAUTION: The following activity needs the teacher’s assistance.
      • Collect the samples of the same metals as in Activity 3.9.
      • Put small pieces of the samples separately in beakers half-filled with cold water.
      • Which metals reacted with cold water? Arrange them in the increasing order of their reactivity with cold water.
      • Answer Sodium, Potassium and Calcium are the metals which reacted with cold water. Their increasing order of reactivity with cold water is => Calcium < Potassium < Sodium
      • Did any metal produce fire on water?
      • AnswerYes, Sodium and Potassium
      • Does any metal start floating after some time?
      • Answer Calcium
      • Put the metals that did not react with cold water in beakers half-filled with hot water.
      • For the metals that did not react with hot water, arrange the apparatus as shown in Figgure and observe their reaction with steam.
      • Which metals did not react even with steam?
      • Answer Copper, Lead,Silver and Gold do not react with water or steem at all
      • Arrange the metals in the decreasing order of reactivity with water.
      • Answer Sodium > Potassium > Calcium > Magnesium > Aluminium >Iron >Lead > Copper > Silver > Mercury
SOLVED EXERCISES : Chapter 3. Metals and Non-metals | CBSE: Class 10th ( Xth ) SCIENCE

Question 1. Which of the following 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.


Answer. (d) AgNO3 solution and copper metal.

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 the above.


Answer.(c) Applying a coating of zinc

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.


Answer.(a) Calcium

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.


Answer.(c) zinc is more reactive than tin.

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.


Answer. We have learnt that Metals are lustrous, malleable, ductile and are good conductors of heat and electricity. They are solids at room temperature, except mercury which is a liquid. Non-metals have properties opposite to that of metals. They are neither malleable nor ductile. They are bad conductors of heat and electricity, except for graphite, which conducts electricity.
(a) Here to distinguish between samples of metals and non-metals using hammer first, we will hammer the given samples of metals and non-metals one by one. We know some metals can be beaten into thin sheets. This property is called malleability. For example gold and silver are the most malleable metals. The samples which, can be converted into thin sheets on hammering hence, are metal where as Non-metal are brittle and can not be beaten into thin sheets.
Secondly, to distinguish between samples of metals and non-metals using a battery, a bulb, wires and a switch we can make use of a property of metal whereby they conduct electric current. To do this, we will arrange the things given a battery, a bulb, wires and a switch and test sample, as shown in the figure below :

The given test sample is connected in searies, and when we turn on the switch, if the bulb glow, given sample is Metal if it does not glow then it is a Non-metal.
(b)The method above is pretty useful except for graphite which despite being a Non-metal is good conductor of electricity.


Question 6. What are amphoteric oxides? Give two examples of amphoteric oxides.

Answer. We know that Metals combine with oxygen to form basic oxides. In general, most of the metal oxide are basic in nature. But some metal
oxides, such as aluminium oxide, zinc oxide, etc., show both acidic as well as basic behaviour. Such metal oxides which react with both acids as
well as bases to produce salts and water are known as amphoteric oxides.
Example (i) Aluminium oxide reacts in the following manner with acids and bases –
Al2O3 + 6HCl2AlCl3 + 3H2O
Al2O3 + 2NaOH2NaAlO2 + H2O
  (Sodium aluminate)
Example (ii) Similiarly Zinc Oxides, Lead Oxide are amphoteric oxides which react with both acids as well as bases to produce salts and water

Question 7. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.

Answer.
(i) Two metals which will displace hydrogen from dilute acids are - Magnesium and Aluminium
(i) Two metals which will not displace hydrogen from dilute acids are - Gold and Copper

Question 8. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?

Answer. In this process, the impure metal is made the anode and a thin strip of pure metal is made the cathode. A solution of the metal salt is used as an electrolyte. The apparatus is set up as shown in Figure. On passing the current through the electrolyte, the pure metal from the anode dissolves into the electrolyte. An equivalent amount of pure metal from the electrolyte is deposited on the cathode. The soluble impurities go into the solution, whereas, the insoluble impurities settle down at the bottom of the anode and are known as anode mud.
Electrolytic refining of copper. The electrolyte is a solution of acidified copper sulphate. The anode is impure copper, whereas, the cathode is a strip of pure copper. On passing electric current, pure copper is deposited on the cathode.

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.
(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.


Answer.
(a)
 (i) The gas will not have any effect on dry litmus.
 (ii) The gas will turn blue litmus red in moist state.
(b) S + O2 → SO2

Question 10. State two ways to prevent the rusting of iron.

Answer. Two ways two ways to prevent the rusting of iron.
(i) Galvanization:  In this method, for preventing the rusting of iron and steel, they are coated with a thin layer of a Zinc. The galvanised iron article is protected against rusting as layer of zinc isolate the iron surface with moist air hence prevent rusting or corssion due to oxidisation..

(i) Painting :  In this method, for preventing the rusting of iron and steel, they are coated with a thin layer of a paint. The painted iron article is protected against rusting as layer of paint isolate the iron surface with moist air hence prevent rusting or corssion due to oxidisation. The galvanised article is protected against rusting even if the zinc coating is broken.

Question 11. What type of oxides are formed when non-metals combine with oxygen?

Answer. When non-metals combine with oxygen, they form either acidic oxide or neutral oxide

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.


Answer:
(a) Platinum, gold and silver are used to make jewellery becuase they are very less.
(b) Metals such as potassium and sodium react so vigorously that they catch fire if kept in the open.Hence, to protect them and to prevent accidental fires, they are kept immersed in kerosene oil.
(c) Aluminium does not corrode and is a very good conductor of heat.
(d) It is easier to obtain a metal from it oxide, as compared to its sulphides and carbonates. Therefore, prior to reduction, the metal sulphides and carbonates must be converted into metal oxides.

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.

Answer. Copper oxide reacts with acids but copper itself does not react. So the copper can be washed by acidic subtances. It removes the corroded part (copper oxide) and pure copper is left behind.

Question 14. Differentiate between metal and non-metal on the basis of their chemical properties.

Answer:
(i) Iron formation: Metals from positive ions and non-metals form negative ions.
(ii) Acidic nature: Metals form basic oxides and non-metals form acidic oxide.
(iii) Reaction with water: Metals react with water but non-metals do not.

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?


Answer. The solution, he used was aqua regia.

Question 16. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron) is not.

Answer. Hot iron reacts with steam formed by boiling water. But, copper does not react with water.

Additional Questions

Question 1. What happens when iron is heated to a high temperature.
Answer. Iron does not burn on heating but glows brightly.

Question 2. What happens when copper is heated to a very high temperature.
Answer. Copper does not burn, but the hot metal is coated with a layer of black substance known as copper(II) oxide.

Question 3. Write an experiment to show that copper does not react with dilute HCI and H2So4.
Answer. The small piece of magnesium, zinc, aluminium, iron and copper. Clean their surfaces by rubbing with a sand paper. Place these metals in separate test tubes. Add about 10 mL dilute hydrochloric acid to each of these test tubes. Observe carefully the rate of formation of bubbles.
We will find that the rate of formation of bubbles was the fastest in the case of magnesium.It decreases in the order Mg > Al > Zn > Fe. In the case of copper does not react with dilute HcI and H2SOO

Question 4. Write the physical properties of metals.
Answer:
(i) All metals except mercury are solid at room temperature.
(ii) Metals possess metallic luster.
(iii) They are malleable and and ductile.
(iv) They are good conductor of heat and electricity
(v) They (except sodium) are sonorous and have high density.
(vi) They are generally hard except sodium and potassium.
(vii) Metals have high boiling and melting points except sodium and potassium.


No comments:

Post a Comment