Question

When an aqueous solution of sodium chloride is electrolysed using platinum electrodes, the ions discharged at the electrodes are:
A. sodium and hydrogen
B. sodium and chloride
C. hydrogen and chloride
D. hydroxyl and chloride

Answer 1

Hint: An electrolytic cell is used to convert chemical energy into electrical energy. In an electrolytic cell, anode is the positive electrode and cathode is the negative electrode. Hydrogen has a lower reduction potential than that of sodium.

Complete answer:
An electrolytic cell is a device that uses electrical energy to conduct a non-spontaneous redox reaction. This takes by the flow of electrons to overcome the barrier of activation energy the non-spontaneous redox reaction. The components of an electrolytic cell are: Cathode (negatively charged) anode (positively charged) and the electrolyte, it provides the medium for the exchange of electrons.
The electrolysis of an aqueous solution of sodium chloride produces aqueous sodium hydroxide, chlorine and the water splits into hydrogen and hydroxyl ions. The electrolysis is represented as
$
  {\text{NaCl}}\,\, \rightleftharpoons \,\,{\text{N}}{{\text{a}}^{\text{ + }}}\,\,{\text{ + }}\,\,{\text{C}}{{\text{l}}^{\text{ - }}} \\
  {{\text{H}}_{\text{2}}}{\text{O}}\,\, \rightleftharpoons \,\,{{\text{H}}^{\text{ + }}}\,\,{\text{ + }}\,\,{\text{O}}{{\text{H}}^ - } \\
$
At cathode, reduction takes place. Here chlorine gas gets oxidised rather than reduction of \[{\text{O}}{{\text{H}}^ - }\]. This is because the reduction potential of \[{\text{N}}{{\text{a}}^{\text{ + }}}\] is less than\[{{\text{H}}^{\text{ + }}}\] . It can be represented as,
\[{\text{2}}{{\text{H}}^{\text{ + }}}\,\,{\text{ + }}\,\,{\text{2}}{{\text{e}}^{\text{-}}}\,\, \rightleftharpoons \,\,{{\text{H}}_{\text{2}}}\left( {\text{g}} \right)\]
At anode, oxidation takes place. \[{{\text{H}}^{\text{ + }}}\] rather than reduction of \[{\text{O}}{{\text{H}}^ - }\]. This is because the potential of oxidation of \[{\text{O}}{{\text{H}}^ - }\] is more as compared. It can be represented as,
\[{\text{2C}}{{\text{l}}^{\text{ - }}}\, \rightleftharpoons \,\,\,{\text{C}}{{\text{l}}_{\text{2}}}\,\,{\text{ + }}\,\,{\text{2}}{{\text{e}}^{\text{-}}}\]
Therefore, hydrogen gas will bubble up at the cathode, and chlorine gas will bubble at the anode.

Hence, the answer to the above question is option C hydrogen and chloride .

Note: In an electrochemical cell a salt bridge is used for connecting oxidation and reduction half cells. A solution of weak electrolyte is used inside this.
Some applications of electrolytic Cells are, it is used to produce oxygen gas and hydrogen gas from water. They can be used for the extraction of aluminium from bauxite.
Electroplating is another major application of electrolytic cells.