Why in one of my lab procedures. I was told to add 6m HNO3 until acidic to litmu

Question

Why in one of my lab procedures. I was told to add 6m HNO3 until acidic to litmus to test for silver (formation of white ppt). Why UNTIL acidic to litmus? Why can't it just be 1 drop

EXPERIMENTAL PROCEDURE: GROUP I CATIONS Test known solution that contains all cations simultaneously with your unknown. Follow the same procedure (separately) for both the unknown and known solutions. Wear gloves during all procedures. Today, STEP 1: Precipitation of Group 1. To 10 drops (only!) of the solution to be analyzed. add 2 drops 6 M HCL. Stir well, Centrifuge and decant the solution (S1) from the ppt (P). Treat the ppu P according to Step 2. (There is no need to wash PL.)-Si-may be tested for the presence of lead as Steps. STEP 2: Dissolving lead Chloride. Add 10 drops of DIwater to Pl and hear to boiling in a water bath for 2-3 minutes. Stir. Immediately centrifuge and decant the solution (S2) into a new test tube while still hot. If any precipitate (now called P2) remains, repeat the process carried out on Pl one more time, decanting the new hot solution into the same 52 test eube. Test S2 according to Scep 3. Treat any remaining P2 as in Step 4. STEP 3: Tesc for lead. To solutions S1 and S2, separately add 2 drops 1 MK.CO Formation of a yellow ppt of PbCro, in either solution confirms lead. STEP 4: Separation of Silver and Test for Mercury. To ppt P2, add 4 drops 15 M NH, Stir. Centrifuge and decant solution (S3). If any solid remains, add another 4 drops 15M NH, stir, centrifuge, and decant solution, combining it with 53. A black ppt formed on the addition of the NH, confirms mercury. Test solution S3 as in Step 5. STEP 5: Test for Silver. To solution S3, add 6 M HNO, until acidic to litmus; add i more drop. Formation of a white ppt of AgCl confirms silver.

Explanation / Answer

To free Ag +from ammonia . so that ammonia can combine with H+ to form stable ammonium ion other ammonical silver remain soluble.

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