Page 175 - Chemistry ICSE Class X
P. 175

Electrolysis                                                                                         161
          Applications of Electrolysis


          How is the principle of electrolysis used in industry
          The principle of electrolysis is used for the following commercial
          applications:
            ƒ  For manufacturing industrial chemicals.
            ƒ  For the extraction of certain metals.
            ƒ  (QT TGſPKPI EGTVCKP OGVCNU
            ƒ  For electroplating.
          These applications are described below.

          Manufacture of industrial chemicals
          Many chemicals which are used in industry in large quantities are prepared
          by electrolysis method. Some of these are:
            ƒ  Sodium hydroxide, NaOH (caustic soda) and chlorine gas, Cl (g) are
                                                                           2
               prepared by the electrolysis of brine (20% sodium chloride) solution.
            ƒ  Hydrogen gas H (g  KU RTGRCTGF D[ VJG GNGEVTQN[UKU QH CEKFKſGF YCVGT
                               2
               or 20% NaOH solution. Oxygen is obtained as a by-product.
          Extraction of metals : Electrometallurgy
            ƒ  More electropositive metals, such as sodium (Na), potassium (K),
               calcium (Ca), magnesium (Mg), aluminium (Al), etc. are obtained by
               the electrolysis of their molten chlorides, hydroxides or oxides. For
               example,
            ƒ  Sodium and potassium are obtained by the electrolysis of their
               molten chlorides and hydroxides. Metals, sodium and potassium, are
               obtained at the cathode:
                                        –
                         Na +      +   e     o       Na
                   from sodium chloride           sodium metal
            ƒ  Calcium and magnesium are obtained by the electrolysis of their
               molten chlorides. Calcium and magnesium are obtained at the cathode.
                                        –
                         Ca 2+     +  2e     o       Ca
                       from calcium               calcium metal
                        chloride
            ƒ  Aluminium is obtained by the electrolysis of its molten oxide (in
               presence of cryolite).
                                        –
                         Al 3+     +  3e     o       Al
                      from alumina                aluminium metal

          Electrorefining (or purification) of metals
          The metals obtained by chemical reduction methods generally contain many     dŚĞ ŵĞƚŚŽĚ ŽĨ ƉƵƌŝĨLJŝŶŐ ŵĞƚĂůƐ
          KORWTKVKGU  5WEJ OGVCNU ECP DG TGſPGF XGT[ GCUKN[ D[ GNGEVTQN[VKE OGVJQF     ďLJ ƵƐŝŶŐ ĞůĞĐƚƌŝĐŝƚLJ ŝƐ ĐĂůůĞĚ
                                                                                       ĞůĞĐƚƌŽƌĞĮŶŝŶŐ͘ DĞƚĂůƐ͕ ƐƵĐŚ ĂƐ
              6JG  RTQEGUU  QH  GNGEVTQTGſPKPI  KU  KNNWUVTCVGF  JGTG  D[  FGUETKDKPI  VJG   njŝŶĐ͕ ĐŽƉƉĞƌ͕ ƐŝůǀĞƌ͕ ŶŝĐŬĞů͕ ŐŽůĚ͕
          GNGEVTQTGſPKPI QH UQOG V[RKECN OGVCNU                                        ĂůƵŵŝŶŝƵŵ͕ ĞƚĐ͘ ĂƌĞ ƌĞĮŶĞĚ ďLJ
                                                                                       ĞůĞĐƚƌŽůLJƟĐ ŵĞƚŚŽĚ͘
          How is copper refined by electrolytic method

            ƒ  Electrolyte. #EKFKſGF EQRRGT UWNRJCVG UQNWVKQP =%W51 (aq) + H SO ]
                                                                                4
                                                                    4
                                                                            2
            ƒ  Ion which carry the current.
                          +
                  2+
              Cu  and H  migrate towards cathode.
                  2–
                            –
              SO  and OH  migrate towards anode.
                  4
   170   171   172   173   174   175   176   177   178   179   180