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Specialty Chemistry Forums => Citizen Chemist => Topic started by: horsebox on December 21, 2009, 12:50:11 PM

Title: Electrolysis of salt water to produce NaOH
Post by: horsebox on December 21, 2009, 12:50:11 PM
If my knowledge is correct when you run current through a NaCl solution chlorine gets freed up leaving a surplus of sodium cations. The sodium will obviously react with the water and form NaOH. I read on a chemistry forum a thread talking about procuring NaOH like this using graphite from pencils as the electrodes. NaOH is cheap and easy to get a hold of but this is still a fairly cool experiment. Wouldn't mind trying it myself. Has anyone here tried this?
Title: Re: Electrolysis of salt water to produce NaOH
Post by: Schrödinger on December 21, 2009, 01:06:47 PM
not tried, but this is the basis of the chlor-alkali industry.

chlor = Cl2
alkali = NaOH
Title: Re: Electrolysis of salt water to produce NaOH
Post by: Borek on December 21, 2009, 01:21:46 PM
Quote from: horsebox on December 21, 2009, 12:50:11 PM
The sodium will obviously react with the water and form NaOH.

That's not exactly true, although the idea (that sodium would react with water) is correct. But in reality it is water that reacts on the electrode producing hydrogen, sodium is not being reduced in water solutions.
Title: Re: Electrolysis of salt water to produce NaOH
Post by: billnotgatez on December 22, 2009, 07:45:33 AM
Borek -

is not the results
hydrogen
Chlorine
Sodium hydroxide
Title: Re: Electrolysis of salt water to produce NaOH
Post by: Borek on December 22, 2009, 08:30:57 AM
Yes, I was refering only to the cathode reaction.
Title: Re: Electrolysis of salt water to produce NaOH
Post by: Doctor science on January 04, 2010, 09:16:19 PM
Quote from: horsebox on December 21, 2009, 12:50:11 PM
If my knowledge is correct when you run current through a Na Cl solution chlorine gets freed up leaving a surplus of sodium cations. The sodium will obviously react with the water and form Noah. I read on a chemistry forum a thread talking about procuring Noah like this using graphite from pencils as the electrodes. Noah is cheap and easy to get a hold of but this is still a fairly cool experiment. Wouldn't mind trying it myself. Has anyone here tried this?
yes i have the aquas solution of table salt will turn green due to the concentration of chlorine if you are using copper to do the experiment. ( heads up... do this experiment in a well ventilated area because I inhaled the chlorine gas and it annoyed me biologically....(burning nose membrane)
Title: Re: Electrolysis of salt water to produce NaOH
Post by: Borek on January 05, 2010, 02:44:27 AM
Quote from: Doctor science on January 04, 2010, 09:16:19 PM
yes i have the aquas solution of table salt will turn green due to the concentration of chlorine if you are using copper to do the experiment.

Pure nonsense. Concentration of chlorine doesn't depend on the copper presence, and color of the solution has nothing to do with the chlorine.
Title: Re: Electrolysis of salt water to produce NaOH
Post by: MrTeo on January 05, 2010, 07:12:51 AM
I tried it once with graphite electrodes (personally I didn't use sharp pencils, but graphite sticks for mechanical pencils with a ∅ of 1 or 2mm) and I din't notice any changement in the solution's colour. Anyway NaOH isn't the only product as Cl2 reacts with OH- giving ClO-:

Cl2+OH-→Cl-+ClO-+H2O

That's why if you sniff next to the solution's surface during the process you'll perceive the characteristic smell of bleach (due to ClO-)  ;D