Electricity and Chemistry (Electrolysis)
What is Electrolysis?
Electrolysis is a process where electricity is used in decomposing / breaking down a compound into its simpler substances. The process takes place in an electrolytic cell that has some main components:-
- A molten ionic / aqueous solution conducting electricity with the help of the ions present. Dissociation of electrolyte leads to formation cations and anions.
- Conducts Electricity
- Electrode attached to positive terminal of battery is called Anode
- And to negative terminal is called Cathode.
The whole electric cell acts as an electric circuit.
Electrons flow from the positive terminal to the negative makes anode positively charged and cathode negatively charged. Anions move to anode and cations move to cathode from the ions present in electrolyte.
Electrolytes decompose when electric current passes through them but metals & graphite remain unchanged. When electrons are gained or lost at the electrodes, it is called as discharge, and after ions get discharged at electrodes atoms or molecules are formed. Redox reactions occur at the electrodes (oxidation at anode and reduction at cathode).
Molten Ionic Compounds
There are many ionic compounds and those ionic compounds that have 2 elements (binary compounds) as its part like Sodium Chloride.
The ionic compound consists of two different ions Na+ & cl–. When Nacl is electrolysed cl– being negatively charged would be attracted to the anode (positive electrode) and Na+ to the cathode (negative electrode). Each Na+ ion would be reduced (gain an electron) to make a sodium atom. Each chlorine ion would oxidize (lose an electron) to form chlorine atom that would combine to form chlorine molecule (cl2).
Aqueous Solutions of Compounds
Electrolysis of Dilute Nacl Solution
In aqueous solution of Nacl there are four ions present as two different ions of Nacl and two ions of water are present.
Na+ & cl– , OH– & H+
It is clearly identifiable that Na+ & H+ would be attracted to the cathode and Na+ & OH– to the anode; but, H+ & OH– get a chance to get an electron and lose an electron.
At the cathode:
2H+ (aq) + 2 e– → H2 (g)
At the Anode
4OH– (aq) → 2H2O (l) + O2 (g) + 4e–
2H2O (l) → 2H2 (g) + O2 (g)
The above reaction took place in an unusual way due to the reactivity series the elements follow.
The lower the element, earlier the element would get discharged.
Another factor that effects discharge is concentration, increase in concentration of the anion would help it to be promoted and get discharged before the other anion present in the solution.
Uses of Electrolysis.
Electro-chemistry has helped a lot in making things easier and efficient on industrial scales as well.
Pure Metals are highly demanded in this age and Electrolytic Purification is one of the efficient ways of making metals pure.
Electrolysis of Copper Sulfate using copper electrodes
Reactive electrodes are used in this process. If the anode is of impure copper and a pure (thin sheet of copper) copper cathode, the copper is transferred from anode to cathode. The anode would start shrinking and cathode would increase in size. The blue color would also remain unchanged of the solution as the electrolyte dos not participate in the process. Only the positive electrode forms copper ions and the at the negative electrode, Cu+2 ions having more ability to accept electrons than H+ ions, a reddish-brown cathode is seen.
At the anode
Cu (s) → Cu+2 (aq) +2e– (anode dissolves)
At the cathode
Cu+2 (aq) +2e– → Cu (s) (cathode becomes copper rich)
This is a very similar process to the previous one as the object that needs to be electro-plated is placed at the cathode and pure substance at the anode. After electrolysis the object gets electro-plated with material at the anode. The process is very efficient as it gives a smooth effect and a single layer that causes a reduction in costs as well. The process makes objects resistant to corrosion while enhance their look.