The Percentage of Chlorine in Sodium Hypochlorite?

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Currently, many municipal water treatment facilities use Sodium Hypochlorite (NaOCl) to disinfect water in one of the stages of the water treatment. I have observed over the years that in practice, most users cannot actually measure the percentage of Chlorine in Sodium Hypochlorite before use for appropriate dosing or injection.

What is the most accurate method or instrument that can measure the percentage of Chlorine in Sodium Hypochlorite with a negligible error margin?

Regards,

Justin

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12 Answers

  1. Don't appologize for me.  One should not encourage to those who go on the net instead of getting out a book and learning. Go back to basic analytical chemistry and study.  Keep in mind, that you have to calibrate instruments, or you can not rely on the readings.  Want to measure something without dilutions?  Wow, not with cocentrated solutions.  In some situations, titrations are best.  

    Perhaps the real problem is the difference between the chlorine applied and the expected results? If so, keep in mind that chlorine can be consumed by the contamination in the water, making the tested results lower than expected.  

    Keep your eyes on the question: "...cannot actually measure the percentate of Chlorine in Sodium Hypochlorite before use..."  

    Wrong!  This is done as standard practive.  He should know that.  He is just lazy!

     Read up on the Hach DPD analysis, and the test ranges. 

  2. Waymon Hofheins is not very encouraging, apologies Chinenye.  I think I know where you are coming from - you want to measure the chlorine content without dilution - e.g. from a salt chlorine generator.  One option to consider is to use an ORP meter, but first calibrate using dilutions and titrations, and then calibrate again from time to time (other salts in the water may also affect the ORP reading).  So while titrations or DPD give the more reliable result, for continuous monitoring of the output of a chlorine from salt generator, you may want to try an ORP probe.  Not sure if anyone else can throw some experience on this??

  3. You are obviously not a chemist; so get off of our board.  If you know nothing about the subject matter, you are just taking up our time.   Too lazy to get a text book? Yes.  Ever heard of a titration method of determining what is in somthing? NO.   FYI sodium Hypochlorite is usually produced as a liquid at about 13%, (or higher) and sold at about 12.5% because it has a loss of chlorine as it forms a gas and exits the container; that is why their is a burp vent in the container bungs.  It gets too hot, it vents.    The high caustic in the liquid is added as a stabilizer, but high pH in the trated water will quickly release chlorine.  Make sense?

    Read tje ptjer good comments below, or get off of the net, and look it up. 

    Now then, did you really study in school?

    1 Comment

    1. Hi Waymon, you failed to answer the question "What is the ​most accurate ​method or ​instrument that ​can measure the ​percentage of ​Chlorine in ​Sodium ​Hypochlorite ​with a ​negligible ​error margin?".

      Don't be sentimental but professional! Look up my profile.

      Here we need practical experience and answers.

      Please can you answer the real question now?

       

      Regards

      Justin (Chemical Engineer)

  4. Anyone try the low salt hypochlorite. Said to have a longer shelf life. We are looking to switch from gas and did a cost analysis, low salt came in at $1.60 to use vs $1.90 per pound Chlorine. The difference is the safety training and equipment up keep. Only supplier I know of is HASA.

  5. At least two factors contribute to the deterioration of hypo in storage: presence of debris in the storage tank that can act as catalysts, and high temps. My company's hypo is received as 20% and we use AWWA B300. For more dilute solutions, like when doing studies where chlorine is dosed at or less than 5 ppm, we are comfortable with the Hach portable DPD method.

  6. Many great answers have been supplied. If you are worried about deterioration you can dilute the delivered chlorine to 6% and the solution will remain stable for a very long time. "0.1 ml hypochlorite in 1 liter volumetric flask" This is the method I would use with a calibrated chlorine analyzer. 

  7. As mentioned in previous replies the available chlorine reduces during storage. Unless you want to confirm the supply quality, I would much rather control the free or total chlorine in the final process steam and adjust the dosing rate to achieve the residual that you require in the actual process stream. I suggest you use a rough estimate of the initial sodium hypochlorite chlorine content (5% or 12-15% whatever the case), calculate a preliminary initial dose and adjust according to the free/total chlorine measured in the actual process stream which is the important control parameter?

    1 Comment

  8. Hi Justin, in addition to the answers provided, it’s also beneficial to understand the age and storage conditions as sodium hypochlorite solution  will deteriorate on standing. Regards Helen 

  9. Joseph is right. 0.1 ml hypochlorite in 1 liter volumetric flack should be in range for a Hach DPD test for both 5% and 12% bleach. LaMotte makes, or made, a high range test kit for % hypochlorite solutions.

  10. Standard Methods for Examination of Water and Wastewater provides accurate methods for the measurement of free and total chlorine. A number of manufacturers, including HACH,  produce field and lab equipment and reagent for quantification of free and total chlorine in NaOCl solution. Please consult Standard Methods and do a web search to find equipment that meets your needs and budget.