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

Some qualitative analysis help

  1. Apr 13, 2010 #1
    hi, so we had a general anion unknown to do that may contain 5 of the following: carbonate, sulfite, chloride, bromide, iodide, oxalate, chromate, sulfide, sulfate, phosphate, nitrate, nitrite, chlorate, acetate, and thiocyanate. I am positive that my unkown had phosphate, iodide, and thiocyanate, and when i tested for sulfate i removed iodide and thiocyanate, removed excess silver ion from past steps by precipitating it out with NaCl, made the soln acidic, added CaCl2, then i added BaCl2 and got NO PRECIPITATE. But then i used another method which was add AgNO3 to my unknown, centrifuge, add HNO3 to the soln, then add BaCl2, and i got a white fluffy precipitate that was insoluble in 6M HNO3, 12M HCl and i heated it in a water bath and it did not dissolve. so my question is did i have sulfate? or could i have reduced/oxidized thiocyanate to sulfate in that step? but i dont think i used any oxidizing/reducing agents in that step, or could it have been some other ppt..??
     
  2. jcsd
  3. Apr 14, 2010 #2

    chemisttree

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    In your second analysis you added Ag and then added a source of chloride. You ppd AgCl. Try dissolving that fluffy stuff in ammonium hydroxide. My guess is that it will be soluble. Not sulfate unless you have some undissolved stuff after you add the ammonium hydroxide.
     
  4. Apr 14, 2010 #3
    You'll notice that you identify which cations are present by combining them with various anions and observing the results, likewise you identify the anions present by reacting them with various cations.
    If you try to run both sets of tests on one test tube of solution, the second set of tests will invariably detect all the reagents you used in the first set.

    The way around this is to split your unknown into two samples, then test one sample for cations only and the other sample for anions only.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Some qualitative analysis help
  1. Qualitative Analysis (Replies: 11)

  2. Qualitative analysis (Replies: 2)

Loading...