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WORKSHEET -1 - metals and non metals

 1.  What are amphoteric oxides? Give two examples of amphoteric oxides.
  • Solution:Amphoteric oxides are the oxides, which react with both acids and bases to form salt and water. E.g. ZnO and Al2O3.
 2.  Name two metals, which will displace hydrogen from dilute acids, and two metals which will not.
  • Solution:Very reactive metals like Zn and Mg displace hydrogen from dilute acids. On the other hand less reactive metals like Cu, Ag, etc. do not displace hydrogen from dilute acids.
 3.  In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte?
  • Solution:Anode is impure, thick block of metal M.
    Cathode is a thin strip/wire of pure metal M.
    Electrolyte is a suitable salt solution of metal M.
 4.  State two ways to prevent the rusting of iron.
  • Solution:By coating the surface of iron by rust proof paints.
    By applying oil or grease to the surface of iron objects so that supply of air consisting of moisture is cut off form the surface.
 5.  What types of oxides are formed when non-metals combine with oxygen?
  • Solution:When non-metals combine with oxygen it forms either neutral or acidic oxides. CO is a neutral oxide; N2O5 or N2O3 is an acidic oxide.
 6.  Give reason

i. Metals replace hydrogen from dilute acids, where as non-metals do not.

ii. Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
  • Solution:i. Metals are electropositive in nature. They readily lose electrons. These electrons reduce the protons liberated from the acid to liberate hydrogen gas, where as non-metals possess a tendency to gain electrons and hence they do not furnish electrons to protons liberated from acids. Hence H2gas is not liberated.
    ii. As it is easier to reduce metal oxides to metal, prior to reduction, metal sulphides and carbonates must be converted to oxides.
 7.  Differentiate between metals and non-metals on the basis of their chemical properties.
  • Solution:

    Metals

    Non-metals

    Metals on heating with oxygen form ionic oxides, which are basic in nature and which dissolve in water to form bases, which turn red litmus blue.

    Non-metals on heating with oxygen form covalent oxides which are acidic in nature and dissolve in water to form acids, which turn blue litmus red.

    Lustrous

    Non-lustrous except graphite

    Conductor of electricity and heat

    Non-conductor of heat and electricity, except graphite

    All are solid except mercury

    Solid-liquid-gaseous

    Electro positive. Loses electrons readily and becomes a positive ion

    Electro negative: gain electrons and become negative ions.

    Metals are reducing agents

    Non-metals are good oxidizing agents
 8.  Explain why the surface of some metals acquires a dull appearance when exposed to air for a long time.
  • Solution:This is due to the surface oxidation of metals when exposed to moist air. For e.g. copper turns green on its surface due to the formation of basic copper carbonate Cu(OH) 2. CuCO3. Similarly silver becomes black due to the formation of black Ag2S and Aluminium forms a white coating of Al2O3 on its surface.
 9.  State which of the following metals would give hydrogen when added to dilute hydrochloric acid. i. Iron, ii. Copper iii. Magnesium
  • Solution:Iron and magnesium react with dilute hydrochloric acid to give H2. Magnesium reacts more readily than iron with dilute hydrochloric acid to liberate hydrogen.
    Fe + 2HCl  FeCl2 + H2
    Mg + 2HCl  MgCl2 + H2
    Cu + HCl  No reaction

    Copper does not react with dilute hydrochloric acid at all. This shows that copper is even less reactive than iron.
 10.  Name a non-metallic element, which conducts electricity.
  • Solution:Carbon in the form of graphite conducts electricity, as there is a free electron in each carbon atom, which moves freely in between the hexagonal layers.

 11.  Which metals do not corrode easily?
  • Solution:Gold and platinum and other noble metals do not corrode in air.
 12.  What are alloys?
  • Solution:Alloys are homogeneous mixtures of two or more metals, or a metal and a non-metal.E.g. steel, brass, bronze, etc.
 13.  Define the following terms.

(i) Minerals

(ii) Ores

(iii) Gangue
  • Solution:(i) MineralsAll compounds or elements, which occur naturally in the earth's crust, are called minerals. Example: Alums, K2SO4.Al2(SO4)3 . 24 H2O, Bauxite Al2O3.2H2O
    (ii) OresThose minerals from which a metal can be profitably extracted are called ores. Bauxite (Al2O3.2H2O) is the ore of Al, copper pyrite CuFeS2. All minerals are not ores but all ores are minerals.
    (iii) GangueWhen an ore is mined from the earth, it is always found to be contaminated with sand rocky materials. The impurity of sand and rock materials present in the ore is known as gangue.
 14.  Name two metals that are found in nature in the free state.
  • Solution:Gold and platinum are found in the free state in nature.
 15.  What is chemical process used for obtaining a metal from its oxide?
  • Solution:The moderately reactive metals such as iron, zinc and copper, etc. in the form of their oxides are reduced to the respective metals by heating with carbon (coke) which is know as carbon reduction method.
    ZnO + C  Zn + CO
    PbO + C  Pb + CO
 16.  Name two metals, which can form hydrides with metals.
  • Solution:Sodium and calcium form stable hydrides on reacting with hydrogen.
 17.  Does every mineral have a definite and a fixed composition? Explain.
  • Solution:Yes, every mineral has a definite and a fixed composition. Minerals are widely distributed in the earth’s crust in the form of oxides, carbonates, sulphides, sulphates, nitrates, etc. These minerals are formed as a result of chemical changes taking place during the formation of earth.
 18.  Explain the meaning of malleable and ductile.
  • Solution:Malleable is being able to be beaten/hammered into thin sheets.
    Ductile is being able to be drawn into thin wires.
 19.  i. Write the electron dot structures for sodium, oxygen and magnesium.

  • Solution:i. Sodium: Na·
    Oxygen: 
    Magnesium: 
    ii. Formation of Magnesium oxide
    When magnesium reacts with oxygen, the magnesium atom transfers its two outermost electrons to an oxygen atom. By losing 2 electrons, the magnesium atoms form a magnesium ion (Mg2+) and by gaining 2 electrons, the oxygen atom forms an oxide ion (O2-).
    Formation of Sodium oxide
    Two sodium atoms transfer their 2 outermost electrons to an oxygen atom. By losing two electrons, the two sodium atoms form two sodium ions (2Na+). And by gaining two electrons, the oxygen atom forms an oxide ion (O2-.)


    iii. The ions present in sodium oxide compound (Na2O) are sodium ions (2Na+) and oxide ions (O2-).
    The ions present in Magnesium oxide compound (MgO) are magnesium ions Mg2+ and oxide ions (O2-).
 20.  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.

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