[matth]

Hello,

I'd like to know of possible methods to make aq. sodium hypochlorite solutions by NaCl electrolysis.

I'm already aware of parameters as keeping the solution cold (to prevent hypochlorite decomposition) and using graphite anode/catode to prevent corrosion.

Is there any particular voltage, NaCl concentration or anything else which could tell me roughly
which percentage of NaClO is there after stopping electrolysis?

Or should I go as (example) performing electrolysis of a saturated NaCl solution at 10°C at 9 volts for 1 hour, then measure the density and refer to an aqueous sodium hypochlorite specific gravity chart to know how much NaClO is there?

Thank you

[marquis]

There are a number of titrations that can be done that will let you measure the amount of NaClO present. 

These titrations are often the same as used for measureing the amount of chlorine in water.  If you are making bleach, you would need to acidify the solution.  The tests usually are sodium thiosulfate based and don't proceed well at high pHs.

Theoretically, if you measured the amount of current that went through the electrodes it could be converted to the amount of bleach produced.  You would have to measure amp hours (including both current and time). 

Good luck.   

[Borek]

Or should I go as (example) performing electrolysis of a saturated NaCl solution at 10°C at 9 volts for 1 hour, then measure the density and refer to an aqueous sodium hypochlorite specific gravity chart to know how much NaClO is there?

Your solution would contain both NaCl and NaClO and density alone would be not enough to determine the composition.

[Ksharindam]

2NaOH+Cl₂=NaCl+NaOCl+H₂O
you can use sodium chloride of any concentration greater than 5%.but high concentration is preferable because of high conductivity.you can determine amount of hypochlorite by mixing urea and measuring the volume of evolved nitrogen.one mole hypochlorite gives 1/3 mole of nitrogen.
3NaOCl+CO(NH₂)2=CO₂+N₂+2H₂O+3NaCl