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Homework Help: What kind of ions co-precipitate with chloride?

  1. Nov 11, 2013 #1
    1. The problem statement, all variables and given/known data

    Question: What kinds of ions may co-precipitate with a chloride ion? (List at least two).

    This is a question for the theory section of my gravimetric analysis lab.
    An unknown chloride salt is mixed into a solution. This solution is to be mixed with a certain quantity of silver nitrate to precipitate out silver chloride, but first the solution is mixed with nitric acid to ensure that no unwanted co-precipitates form. Specifically, the nitric acid is mixed in to ensure that any carbonate ions that may be present within the solution are converted to carbon dioxide gas and water (if somebody could tell me why carbonate ions would even be in this solution in the first place, that'd be awesome too). Otherwise, carbonate ions may precipitate to form silver carbonate and the analysis will be ruined.

    2. Relevant equations

    I know that in this solution, there are H+ ions, Ag+ ions, Cl- ions and NO3-- ions.
    What I'm trying to find are two ions that may form a precipitate with Cl-.

    3. The attempt at a solution

    I've only been able to find 1 possibility so far, being the formation of NH4Cl.
    NH4+ + Cl- --> NH4Cl

    Thanks ahead of time for any/all help given.
    Last edited: Nov 11, 2013
  2. jcsd
  3. Nov 12, 2013 #2
    I assume the silver precipitates out along with the chloride ion, since the salt is insoluble and that is the precipitate you are trying to make in this case. Ammonium chloride is soluable in water, so it will not form a precipitate.

    Is the analysis below the question different from the question? Many ions co-precipitate with chloride, but the only one I see in the expanded question/analysis is silver.
  4. Nov 12, 2013 #3
    Yeah, the goal is to use ALL of the chloride ions from the unknown salt to form silver chloride. However, when the chloride ions are dissociated, they also supposedly interact with other ions in the solution, so not all of them are used in creating the silver chloride precipitate, which results in a certain degree of error.

    Sorry if the question's confusing. What I'm asking is: in a solution that contains ONLY the previously mentioned ions (H+ ions, Ag+ ions, Cl- ions and NO3-- ions), what ions exist or can be formed (other than silver ions) that can react with the chloride ions? I'm supposed to provide two examples where chloride ions can be used up in reactions with ions other than silver.
  5. Nov 13, 2013 #4


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    Staff: Mentor

    The more similar the ion, the higher the chance it will coprecipitate. First suspects are halides and pseudohalides. Then every ion that creates low solubility silver salts (that means almost everything).
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