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While searching how to identify cations in a solution I found that ammonia could be used to distinguish between $\ce{AgCl}$ and $\ce{PbCl2}$ precipitates after $\ce{HCl}$ had been added.

Why does the addition of ammonia cause $\ce{PbCl2}$ to dissolve while $\ce{AgCl}$ doesn't? (With chemical equations if possible.)

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    $\begingroup$ Are you sure you have this right? I thought the silver compound was the one that dissolves. $\endgroup$
    – Oscar Lanzi
    Commented Jul 13, 2019 at 9:43
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    $\begingroup$ I used to do this lecture demo: add NaCl soln to silver nitrate soln to precipitate AgCl. Then add concentrated ammonia soln to dissolve the AgCl. Then add KBr soln to precipitate AgBr. Then add sodium thiosulfate soln to dissolve the AgBr. Then add KI soln to precipitate AgI. Then add KCN soln to dissolve the AgI. (I skipped the last step in the lecture hall, for safety reasons.) I suggest looking up the various silver complexes than can form. Also, if I remember correctly, there are both silver and lead chloro complexes and HCl was used initially. Hope this helps and +1 to Oscar Lanzi. $\endgroup$
    – Ed V
    Commented Jul 13, 2019 at 14:02
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    $\begingroup$ @Oscar Lanzi is correct ,Silver ion in ammonia solution forms a soluable complex. $\endgroup$
    – Chakravarthy Kalyan
    Commented Jul 13, 2019 at 16:35
  • $\begingroup$ Furthermore $\ce{PbCl2}$ is not soluble in ammonia solutions. If does not form any lead-ammonia complexes. $\endgroup$
    – Maurice
    Commented May 18 at 12:19

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The answer lies in the comment section itself. Silver chloride dissolves in ammonia due to Le Chatelier's principle. For more details, see: What is the reason for the different solubility of silver halides in ammonia?

Lead chloride does react with aq. ammonia, forming a white precipitate of lead hydroxide + basic lead hydroxide and this precipitate doesn't dissolve in excess ammonia. See: https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_(Analytical_Chemistry)/Qualitative_Analysis/Characteristic_Reactions_of_Select_Metal_Ions/Characteristic_Reactions_of_Lead_Ions_(Pb)

On the other hand, silver chloride initially forms a brown precipitate of silver oxide due to incomplete reaction with aq. ammonia.

$$\ce{2Ag+ + 2NH3 + H2O -> Ag2O \downarrow + 2NH4+}$$

Over time, the reaction reaches equilibrium and dissolves in excess of ammonia forming the diammineargentate complex (note that this solution has to be discarded immediately after reaction to avoid forming silver nitride which is an explosive).

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