The Systematic Analysis of Cation Group I

The ions in Cation Group I are precipitated as insoluble chlorides by adding a little excess of chlorine ion solution such as hydrochloric acid. There are about five ions of elements showing insolubility on the periodic table. They are Cu(I), Ag(I), Au(I), Hg(I), Tl(I), Pb(II).


Outline

 Take the suitable sample of solution in a centrifuge tube add 1 drop 6M HCl and stir. If precipitate forms, add another drop of HCl to test for completeness of precipitating. Continue add HCl until no more precipitate forms, but avoid add too much. Stir for 1~2 minutes to give time for slow precipitating of PbCl₂. Centrifuge using another centrifuge tube filled with an equal volume of water as a counterbalance. Withdraw as much as possible of the clean solution with a pipet. Transfer solution to a test tube and check again for completeness of precipitating. Wash the residue with few drops very dilute HCl.

 Testing Sample

 Testing sample was treated with hydrochloric acid

and formed a lot of white precipitate.

And then add about 5 drops of distilled water. Warm it in hot water bath and stir occasionally for a few minutes. Centrifuge and separate solution from precipitate quickly. Transfer solution to a test tube.

 

 In hot water bath to dissolve PbCl₂ into hot water

 And then centrifuge the solution to separate solid and liquid

Solution 1-2. Pb²⁺, PbCl⁺, Cl^-.

Add 1 drop 6M HOAc and several drops K₂CrO₄. Yellow precipitate, PbCrO₄: presence of Pb

 Yellow precipitate form immediately when added K₂CrO₄

Add several drops of 15M NH₃. Use a rob to disperse caked residue in the reagent. Centrifuge it. Transfer solution to a test tube.

 Black to gray precipitate formed. It was composed of HgNH₂Cl, Hg⁰(black)

Black residue shows there were Hg₂²⁺ in the solution.

Solution 1-3 Ag(NH₃)₂⁺, Cl^-, NH₃.

Acidify with 6M HNO₃. Verify with litmus. White precipitate, AgCl: presence of Ag

 

 White precipitate(AgCl) formed

 Experimental Record