Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Test for Halides/Halogens

  1. Oct 23, 2006 #1
    Is there an inexpensive way to test for Halides/Halogens and put a rough quantity/concentration on the content?

    Second, could Ethylene Dichloride cause a halogen test to come up positive? If so, what kind of amounts to produce 1ppm in a gallon of water would be needed?

  2. jcsd
  3. Oct 25, 2006 #2

    you can test very easily for Cl and Br by using mass spec. (this depends if the mw of your compound is in the mass range for your instrument though). quantitative analysis would be harder. you would have to make standardized concentration curves probably, it is a pain. if ethylene dichloride is a contaminant in your product, it should show up on the NMR, which would also give you a handle on how much is in there as well. 1 L of water is 55.5 moles of H20. so if you had 1 ethylene dichloride molecule per 1million h20 (ok it is 1 in 999,999 but just use 1 million to make calculations easier, it wont be off by that much) molecules, you should be able to figure out easily how many molecules of ethylene dichloride are in 1 gallon of water with a concentration of 1ppm of ethylene dichloride.
    Last edited: Oct 25, 2006
  4. Oct 26, 2006 #3
    Let me see if I am getting my calculations right ---

    If I scale up to a barrel -- about 208 L -- I should have about 11544 moles of H2O. Now, if I want to obtain a 25,000 ppm of eth. dichl., I would want a ratio of 25k molecules of eth dichl./974,000 molecules water. multiply that ratio back by 11544 and I get 296 moles of eth. dichl. I should need for my concentration.

    The molar density of eth. dicl is about 99 g/mol. so 296*99 = 29304 g total eth dichl I need. With a denisty of 1.253 g/cm3, I get roughly 23 Liters of Eth. dichl. per barrel of water to get a concentration of 25,000.

    Sound reasonable??
  5. Oct 26, 2006 #4
    looks good
  6. Oct 27, 2006 #5


    User Avatar
    Science Advisor
    Homework Helper

    Quantitative analysis for some halides involve gravimetric analysis, for instance with Cl-, one can add AgNO3 to form AgCl (assuming that the solution isn't severely contaminated) and this precipitate can be dried, then weighed. The chloride content can be calculated indirectly through knowledge of the stoichiometric aspects of the experiment.

    Another quick way to determine the chloride, or halogen content, is through electrochemical methods. Chloride, in particular, is a common agent in electrochemistry; e.g. AgCl reference electrode.

    If you wanted to analyze ethelene dichloride, you would probably need to employ some standard organic chemical methods or use relatively more advanced chemical instrumentation/methods.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook