The Electrolysis of Sodium Chloride.

Apparatus

• Aqueous sodium chloride (brine)
• Wires
• Crocodile clips
• Light Bulb
• Electrodes
• Test tubes x 3
• 12V battery pack

Method

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. 

Diagram

Observations

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.  

Conclusion

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-  
                                                                            Cation                Anion

2. Reaction at the cathode:        Na +    +    1e-        →        Na        (neutralization) 
     

3. Reaction at the anode:         Cl-                     →        1e-  +        Cl        (neutralization) 

                                                    Cl       +    Cl         →                Cl2