Edison
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Quantitative analysis of NaClO solutions
Hey,
What is the best way to analyse the concentration of NaClO in a mixed NaCl + NaClO aqueous solution, formed from electrolysis?
By best I mean quick, convenient and accurate within 1%.
I thought about adding dilute hydrogen peroxide and measuring the volume of O2, but H2O2 is not easy to get these days.
What about heating the solution strongly? At what temperature does NaClO decompose, and will it decompose only as follows:
2NaClO -> 2 NaCl + O2
The gas that comes off will be a mixture of water vapor and oxygen. Can I separate the two by just bubbling the gas through a water trap?
Thanks.
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gdflp
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No it will mainly decompose as follows, 3NaClO --> 2NaCl + NaClO3. Adding some HCl and measuring the amount of chlorine gas which results may be
suitable.
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Edison
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Thanks. I thought about that, but Cl2 is fairly soluble in water at RTP.
Should I keep the water hot, at say 90 Celcius, to reduce Cl2's solubility?
Would the reaction between NaClO and HCl be as follows:
NaClO + HCl -> NaOH + Cl2
Effectively the addition of HCl reverses the reaction between the Cl2 formed at the anode and the NaOH formed at the cathode, which combined to form
NaClO + NaCl?
So I can deduce that one mole of Cl2 gas would be formed from one mole of NaClO?
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blogfast25
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Yes.
2 H+ + ClO− + Cl− < === > Cl2 + H2O
Very low pH shifts it completely to the right.
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gdflp
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Yes, but as blogfast said, the reaction won't be NaClO + HCl --> Cl2 + NaOH, it will be NaClO + 2HCl --> H2O + NaCl+Cl2
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Edison
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OK thanks guys 
I presume keeping the water hot will work to reduce the solubility of the chlorine gas in it.
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macckone
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Heating hypochlorite or chlorine solution results in conversion via the same pathway as listed by gdflp. The following has the correct test
procedure:
www.okbu.net/chemistry/mrjordan/hslabs/bleach2.pdf
Try the following google search for more links:
https://www.google.com/search?q=determination+of+the+concent...
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