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| The Process of Electrolysis |
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| According to the theory of electrolytic dissociation, electrolytes can be electrolysed only in the dissolved or molten state. These charged ions are directed towards the respective electrodes by the electricity supplied. |
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| Let us examine the process of electrolysis in an electrolytic cell when the electrolyte used is molten sodium chloride. |
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| Electrolysis of Molten Sodium Chloride |
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| When sodium chloride is formed the sodium atom donates an electron to the chlorine atom to form an electrovalent bond. Hence in the process: |
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 Sodium atom loses an electron and becomes positively charged (Na+). |
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Chlorine atom gains an electron and becomes negatively charged (Cl-). |
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The electrolyte consists of sodium (Na+) and chloride ions (Cl-) (Fig.4.8). |
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| Before the electric current is switched on, the ions in molten state, through mobile, have no direction of movement. They move only randomly. But when molten sodium chloride is electrolysed (the current is switched on), the ions follow a particular direction of movement. |
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| The cell set up is shown in Figure 4.9. The electrodes in this case are of carbon. |
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| The electrolysis of molten sodium chloride is as follows: |
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| In solution or molten state, when dissociation takes place, the sodium ion has a positive charge and the chloride ion has a negative charge. |
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| These ions are capable of carrying the current. The positively charged ions Na+ migrate to the cathode, and the negatively charged ions Cl- migrate to the anode. On reaching the respective electrodes these ions get involved in electrochemical reactions at the electrode and form their respective products. |
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| At cathode |
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| The cathode is a region of surplus electrons. The ion that migrates to the cathode is the positively charged ion or cation i.e., sodium ion. |
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| At the cathode, the ions accept electrons. The sodium ion takes in one electron from the cathode, gets converted into a sodium atom, and gets deposited at the cathode. Hence reduction takes place at the negative electrode or cathode. |
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| The product obtained at the cathode is sodium metal. |
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| In general, the number of electrons gained by the cation depends upon the number of positive charges it carries. For example an aluminium ion has three positive charges. Hence it will gain three electrons to get converted into an aluminium atom. |
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| At anode |
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| The anode is a region of deficiency of electrons and hence anions give up electrons here. They migrate to the anode to give up as many electrons as they have negative charges. Hence the electrode at which oxidation takes place is anode (the positively charged electrode). |
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| In this case, the chloride ion has one negative charge that it has gained from sodium. This electron is given up to the anode and chlorine is deposited in the form of bubbles of greenish yellow chlorine gas. |
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| In other words, the product obtained at anode is chlorine gas. |
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| It should be very clear that in the above electrolysis, the electrons flowing through the bulb are not the electrons that are produced by the battery. These electrons are accepted by the cations from the electrolyte. The electrons passing through the bulb are the ones given up by the anions. |
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Cations are cathode-seeking ions, and anions are anode-seeking ions. The ions of a particular charge migrate to the electrode of the opposite charge. |
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This flow of ions generates electricity, which can be used for doing some useful work. Thus, in an electrochemical reaction the decrease in the chemical energy is liberated in the form of electrical energy. |
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| The various differences between passage of electricity through a metal and an electrolyte are given in the table below. |
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