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6 CHEMICAL PROPERTIES OF METALS



       Metals are also called electropositive elements because the metal atoms form positively charged ion by losing electrons. Following are the important chemical reactions of metals which takes place due to the electropositive character of metals.

1. Reaction of Metals with Oxygen

       Almost all metals react with oxygen to form metal oxides. But different metals react with oxygen at different intensities. For example, sodium metal is always kept immersed in kerosene oil. Because, if we keep it open, it reacts so vigorously with oxygen present in air that it catches fire. We have already discussed that the oxides of metals are basic in nature. As all the metals have different reactivity so they combine with oxygen at different temparature.

  1. Sodium metal reacts with oxygen of air at room temperature to form basic sodium oxide.

                   4Na      +      O2           2Na2O
                 Sodium       Oxygen                           Sodium oxide

  2. On heating, magnesium metal burns in air giving magnesium oxide.

                   2Mg      +      O2           2MgO
              Magnesium     Oxygen                         Magnesium oxide

  3. Zinc metal burns in air only on strong heating to form zinc oxide.

                   2Zn      +      O2           2ZnO
                   Zinc          Oxygen                            Zinc oxide

  4.        Generally, metal oxides are insoluble in water. But some metal oxides are able to dissolve in water to form metal hydroxides (or alkali). For example, oxides of sodium and potassium dissolve in water to form sodium hydroxide and potassium hydroxide respectively.

                Na2O      +      H2O           2NaOH
           Sodium oxide       Water                          Sodium hydroxide

                 K2O      +      H2O           2KOH
        Potassium oxide    Water                        Potassium hydroxide

In the same way sulphur reacts with oxygen of air to form acidic sulphur dioxide.

S      +      O2           SO2
     Sulphur                                         Sulphur Dioxide



2. Reaction of Metals with Water

       Metals react with water to produce metal oxide (or metal hydroxide) and hydrogen gas. But, all metals do not react with water at equal intensity. The metals which are very reactive can react even with cold water while the other metals react with hot water or with steam. For example:


  1. Sodium, potassium and calcium metal can react with cold water to produce their hydroxides and hydrogen gas.

         2Na      +      2H2O           2NaOH     +     H2
       Sodium           Water                           Sodium hydroxide

         2K      +      2H2O           2KOH    +     H2
    Potassium        Water                        Potassium hydroxide

         Ca      +      2H2O           Ca(OH)2     +     H2
    Calcium           Water                          Calcium hydroxide

  2. Magnesium, zinc and iron react with hot water to produce metal oxide and hydrogen gas.

         Mg      +      H2O           MgO     +     H2
    Magnesium      Water                       Magnesium oxide

         Zn      +      H2O           ZnO     +     H2
        Zinc           Water                              Zinc oxide

         3Fe    +    4H2O           Fe3O4    +    4H2
         Iron          Water                               Iron oxide

3. Reaction of Metals with Dilute Acids

       When a metal reacts with a dilute acid then a metal salt and hydrogen gas are formed. For example:

       Sodium, magnesium and zinc reacts with dilute hydrochloric acid to form their salts and hydrogen gas.

           2Na      +      2HCl           2NaCl     +     H2
         Sodium   Hydrochloric acid                   Sodium chloride

           Mg      +      2HCl           MgCl2     +     H2
     Magnesium   Hydrochloric acid            Magnesium chloride

           Zn      +      2HCl           ZnCl2    +    H2
          Zinc    Hydrochloric acid                    Zinc chloride

4. Reaction of Metals with Salt Solutions

       If a more reactive metal is put in the salt solution of a less reactive metal, the more reactive metal displaces the less reactive metal from its salt solution. These reactions are called displacement reaction. For example:

Reaction of Copper with Silver Nitrate Solution.

       If a piece of copper metal is placed in colourless solution of silver nitrate for some time, the colour of the solution becomes blue and a shining white deposit of silver metal is formed on the piece of copper. Actually, in this reaction copper metal is more reactive than silver present in silver nitrate solution. So, copper displaces silver from silver nitrate solution to form copper nitrate and silver metal.

       Cu     +     2AgNO3        Cu(NO3)2     +      2Ag

     Copper          Silver nitrate                                  Copper nitrate              Silver
                       (Colourless solution)                         (Blue solution)       (White deposit)


Reaction of Zinc with Copper Sulphate Solution

       If a piece of zinc metal is placed in blue coloured solution of copper sulphate for some time, the blue colour of copper sulphate solution fades away. This happens due to the formation of colourless solution of zinc sulphate .you will also observe that during this reaction red brown copper metal deposits on the piece of zinc.
       In this reaction zinc is more reactive metal than copper present in copper sulphate solution. So, zinc displaces copper from copper sulphate solution to form zinc sulphate and copper.

       Zn     +     CuSO4        ZnSO4      +       Cu

        Zinc        Copper sulphate                            Zinc sulphate            Copper
                       (Blue solution)                          (colourless solution)   (red-brown)

Reaction of Iron with Copper Sulphate Solution

       If iron fillings are placed in the blue coloured solution of CuSO4 for some time, the blue colour of copper sulphate solution turns into greenish colour and red brown precipitate of copper get deposited over iron fillings.

       Fe     +     CuSO4        FeSO4      +       Cu

        Iron        Copper sulphate                            Iron sulphate            Copper
                       (Blue solution)                             (Greenish sol)        (red-brown)

5. Reaction of Metals with Chlorine

       All metals react with chlorine to form ionic metal chlorides. For example:

                  2Na       +       Cl2            2NaCl
                Sodium         Chlorine                          Sodium chloride

                  Ca       +       Cl2            CaCl2
              Calcium         Chlorine                         Calcium chloride

                  Mg       +       Cl2            MgCl2
            Magnesium      Chlorine                      Magnesium chloride

                  Zn       +       Cl2            ZnCl2
                 Zinc           Chlorine                          Zinc chloride

6. Reaction of Metals with Hydrogen

       Only a few metals like Na, K, Ca and Mg react with hydrogen to form metal hydrides.

                  2Na       +       H2            2NaH
                Sodium        Hydrogen                         Sodium hydrides

                  Ca       +       H2            CaH2
               Calcium       Hydrogen                      Calcium hydrides


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