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Author Topic: How does electrolysis of molten sodium chloride and brine differ?  (Read 12158 times)

Offline Matthew

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Mav asked the Naked Scientists:
   
What is the difference between electrolysing NaCl - sodium chloride - and setting up a circuit with salt in water? Is it the ions pass electrons in a circuit whereas the ions are attracted to the electrodes in electrolysis?

What do you think?


 

Offline Chemistry4me

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When a dilute solution of sodium chloride is electrolysed, water is oxidised at the anode in preference to chloride ions.

2H2O → O2 + 4H+ + 4e-

Water is also reduces at the cathode in preference to sodium ions.

2H2O + 2e- → H2 + 2OH-

In the electrolysis of dilute sodium chloride, water is 'splt' into its elements rather than NaCl being split into it's elements.

If a concentrated solution of sodium chloride (called brine) is electrolysed, chloride ions are in high enough concentration to be oxidised at the anode in preference to water.

2Cl- → Cl2 + 2e-

Water is reduced at the cathode because Na+ ions are poorer oxidising agents than water. Given the explosive nature of sodium metal with water, it is obvious that sodium metal does not form when aqueous solutions of it's ions are electrolysed.
 

Offline Atomic-S

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In molten sodium cloride, we would be talking about a completely anhydrous situation. In such a situation, there is no water to electrolyse, resulting in the breakdown of the salt into Na and Cl.
 

Offline Chemistry4me

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Whoops, sorry, I obviously did not read the question properly
 

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