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Sodium thiosulfate

  1. Oct 27, 2009 #1
    How would I figure out the formula for Sodium Thiosulfate?

    I was asked that question on an exam and I knew sodium sulfate was Na2SO4, so I figured ok, thio means sulfur, so I'll just add another S like this:


    But my prof said Na2S2O3
    was the right answer, and I have no idea how I was supposed to know there were only 3 O's, since it's not sulfite.
    Wikipedia agrees with him, tho.

    Any ideas?

  2. jcsd
  3. Oct 27, 2009 #2
    You're replacing an Oxygen atom with a Sulfur atom. The original compound is Sodium Sulfate, which is Na2SO4, but when it becomes Sodium Thiosulfate, one of the Oxygen atoms is replaced with a Sulfur atom. So it becomes N2S2O3.

    If it were to be Sodium Dithiosulfate, you would replace 2 Oxygen atoms with 2 sulfur atoms, so it would be N2S3O2
  4. Oct 28, 2009 #3
    Also, consider that in your formula: Na2S2O4 sulfur would have oxidation number = 3, which doesn't exist (for sulfur).
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