Question

What are the products of electrolysis of molten and aqueous sodium chloride?

Answer 1

Hint: A process in which electric current is passed through a substance in order to affect its chemical properties is known as electrolysis. During the process, a chemical change is observed in which the substance either loses electrons to undergo oxidation or gains electrons to show reduction.

Complete answer:
Electrolysis of molten sodium chloride: If sodium chloride $(NaCl)$ is melted above ${801^o}C$, two electrodes are inserted into their molten state and an electric current is passed through it. Then it is observed that, liquid sodium floats to the top of the melt above the cathode and chlorine gas is bubbled out of the melt above the anode. The chemical changes taking place at electrodes are as follows:
Cathode: Sodium ions migrate to cathode and get reduced to sodium metal. The reaction is as follows:
$N{a^ + } + {e^ - } \to Na$
Anode: Chloride ions migrate towards the anode and are oxidized to chlorine gas by losing electrons. The reaction is as follows:
$C{l^ - } \to \dfrac{1}{2}C{l_2} + {e^ - }$
The overall reaction for electrolysis of molten sodium chloride can be represented as follows:
$2NaCl \to 2Na(s) + C{l_2}(g)$
Electrolysis of aqueous sodium chloride: The electrolysis of aqueous $NaCl$ results in hydrogen and chlorine gas. At anode, the chloride ions are oxidized to chlorine whereas at cathode, water is reduced to hydroxide and hydrogen gas. Since water can be both oxidized and reduced, it completely dissolves the ions of sodium chloride and rather than producing sodium, hydrogen gas is liberated. The chemical reactions taking place at each electrode are as follows:
Cathode: ${H_2}O(l) + 2{e^ - } \to {H_2}(g) + 2O{H^ - }$
Anode: $C{l^ - } \to \dfrac{1}{2}C{l_2}(g) + {e^ - }$
The overall reaction for electrolysis of aqueous sodium chloride can be represented as follows:
$NaCl(aq) + {H_2}O(l) \to N{a^ + }(aq) + O{H^ - }(aq) + {H_2}(g) + \dfrac{1}{2}C{l_2}(g)$

Note:
It is important to note that the reason for the difference in electrolysis of aqueous and molten sodium chloride is that the reduction of sodium ion i.e., $N{a^ + }$ is energetically more difficult than the reduction of water. Thus, the reduction of water takes place instead of sodium, in case of aqueous sodium chloride.