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Electrolysis Products

  1. Jan 1, 2012 #1
    I am a 9th grader working on a science fair project to determine which salt, NaCL or MgCL produces the most hydrogen gas through electrolysis. I used 1.5 ml of water for each, and 17.5 mg of each salt respectively. After 1 hour of applying a 2.5 amp current through each sample, the NaCL solution formed a brownish residue, while the magnesium chloride solution had turned milky white. What reactions had taked place, and what were the product(s)?

    P.S. The wires in the water were copper.
  2. jcsd
  3. Jan 1, 2012 #2


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    Gold Member

    sure it 1.5ml of water???

    You do not state what voltage .

    NaCl solution
    You have ions H+, Na+, Cl-, and OH- in solution
    The electrode is copper and that can form oxidatin states of +1, +2, +3, +4

    You know that the other ions can form compounds but not with a brown color,

    so the brownish residue is some sort of copper compound assuming only +1, +2 oxidation
    It could be CuOH, CU (OH)2, , Cu2O, CuCl, Cu Cl2

    Does that help you out?
  4. Jan 1, 2012 #3
    Thanks so much! Have any thoughts on the MgCl2 solution?
  5. Jan 1, 2012 #4


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    Do the same thing for the MgCl2 solution.
    When the solution is prepared, what species are present in solution.
    Then, as the electrolysis is performed what compounds have a possibility of being formed.
    Of those compunds, what forms a milky white precipitate suspended in the water, but most likely something to do with Mg.

    Note that for the NaCl solution you still have to decide which one compound has formed the browniish residue, instead of a brownish liquid, which since you say residue is not soluable in water.

    You still have some more research to do.
    Come back if you have some more questions.

    Sorry if I appear to be vague but you trying to find out what the precipitates are will give you tremendous insight into chemical reactions.
  6. Jan 1, 2012 #5


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    Staff: Mentor

    Do you know Faraday's law of electrolysis?
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