Krishaan Siva – L6CMK
The Electrolysis of Sodium Chloride
Electrolysis is a process by which electrical currents can be passed through solutions. Pure water is a non-conductor of electricity. But if a salt such as NaCl is dissolved in it, the solution will start conducting if two electrodes are placed in it along with a battery that provides the initial current.
When an electric current is passed through a chemical compound, some compounds are able to conduct electricity. The compound dissociates into ions under the influence of the electric current. The electrical current initiates a chemical reaction or a break up. The sodium chloride or brine is an electrolyte. An electrolyte is a compound that allows electric current to pass through itself, when either in a molten state or in an aqueous solution
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- Aqueous sodium chloride (brine)
- Crocodile clips
- Light Bulb
- Test tubes x 3
- 12V battery pack
We took two lead electrodes, a 12V battery pack, a bulb and some wires. We put the sodium chloride into a special beaker that contained the two lead electrodes. We then took two more small test tubes and put them over the electrodes so that we could collect the chlorine and the hydrogen gas that would be given off during the process. We had to make sure that the two smaller test tubes were not touching the bottom of the bigger test tube otherwise the ionic exchange would not take place.
NaCl is an ionic compound and both the Na+ and the Cl- ions are strongly attracted to each other by electrostatic attraction. The strength of the electrical current is unable to break the ionic bond. Not only breaking of the ionic bond is needed, the flow of charges also has to take place. This does not happen in solid NaCl. Thus solid NaCl is not an electrolyte.
In aqueous solution of NaCl, water molecules separate the Na+ and the Cl- ions. This makes them very mobile. The mobility is enhanced when two electrodes in the form of anode (+) and cathode (-) are inserted in the salt solution. The Na+ ions get attracted toward the cathode and the Cl- ions get attracted toward the anode. The aqueous solution of NaCl is therefore a good electrolyte.
We can conclude from the above discussions that the movement of ions is responsible for the flow of current in an electrolytic cell. Below are the steps occurring during the passage of electricity in an electrolytic cell with NaCl aqueous solution:
1. Dissociation of NaCl: NaCl ⎯→←⎯ Na + + Cl-
2. Reaction at the cathode: Na + + 1e- → Na (neutralization)
3. Reaction at the anode: Cl- → 1e- + Cl (neutralization)
Cl + Cl → Cl2