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Precipitation of Metal Chlorides

  1. Jul 25, 2014 #1
    1. The problem statement, all variables and given/known data
    A colorless solution is known to contain one of these ions. Which ion is present if adding dilute HCl produces a white precipitate that dissolves when the solution is warmed?

    A) Ag+
    B) Cu2+
    C) Hg22+
    D) Pb2+

    2. Relevant equations
    N/A

    3. The attempt at a solution
    The only one I could really rule out was copper chloride, as it is soluble. I'm stuck because I know that AgCl, Hg2Cl2, and PbCl2 are all white precipitates. Without using a chart, how can I determine qualitatively which dissolves in a warmed solution? Thank you in advance.
     
  2. jcsd
  3. Aug 13, 2014 #2
    I'm sorry you are not generating any responses at the moment. Is there any additional information you can share with us? Any new findings?
     
  4. Aug 13, 2014 #3

    epenguin

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    I'd say there is know way of knowing this except just knowing it.

    There are a few facts about solubility you really should know. Most nitrates soluble, AgCl, BaSO4 outstandingly insoluble. I remember those two from seeing so often in qualitative chemistry demonstrations and experiments. In practical 'qualitative analysis'. And quantitative analysis - which depends on their extreme insolubility. And then do you know about barium enemas? All knowledge hooks like that help.

    So if I were answering the question I would have answered Ag+ as they imply only one answer is right. :biggrin:

    I have an almost totally washed out memory of the other two dissolving slightly when heated. But it is not exactly a piece of knowledge I ever used every day.

    I have an even fadeder memory of something about lead pipes being used for drinking water (which is slightly acid) since the time of the Romans (a few of whom lived till 50 and even longer) but that there were problems when running hot water was invented, or when some lead was used in metal cooking pots. That may not be true but it helps remember.

    You can find stuff by google.

    http://www.public.asu.edu/~jpbirk/qual/qualanal/lead.html

    www.youtube.com/watch?v=LaWdhxlvEAE
     
  5. Aug 19, 2014 #4
    I dont know if you've studied Qualitative Inorganic Analysis yet, but the ions which get precipitated but dil. HCl are called Group I ion, which are Ag+, Hg2+, and Pb2+. Upon adding the reagent they precipitate as chlorides. SInce they gave that the precipitate dissolves when the solution is warm it indicated that the chloride is PbCl2, as it has an interesting (and important!) property that it is soluble in warm water. So the answer is D
     
  6. Aug 19, 2014 #5

    epenguin

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    Sorry I had
    misread or something, my answer was if it does not dissolve when heated.
     
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