You are given an unknown sample that when treated with hydrochloric acid forms a

Question

You are given an unknown sample that when treated with hydrochloric acid forms a precipitate. After decantating the liquid, you add boiling water to the remaining solid. Some of the solid disappears. You decant the solution and add a few drops of K2CrO4;. No yellow solid appears. With the solid left from the addition of boiling water, you add ammonium hydroxide and centrifuge the product. No gray/black solid is present. You then decant the liquid and add concentrated nitric acid until the solution is acidic; a white precipitate forms. Which group 1 cations were present in your unknown? Which group 1 cations were not present in your unknown?

Explanation / Answer

step given :

The formation of precipitate on treating with HCl confirms the presnce of Group 1

If some of the solid dissappears in this step ,it shows lead may be present

The above annalysis shows the presence of Lead cation of group 1

and absence of Mercury and silver cation of group 1

Explanantion:

The group 1 contains three cations lead, silver and mercury.

According to scheme of cation ananlysis on treatment with HCl -----> Precipitate forms

It may contain AgCl , PbCl2 or Hg2Cl2

Precipitate + hot water -----> Precipitate forms ( silver or Mercury may be present)

If ppt dissolves then lead may be present

further on treatment with ammonium hydroxide , centrifugation and then making the solution acidic by concentrated Nitric acid forms the white precipitate, which shows the presence of Lead cation.

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