Page 65 - Chemistry - XI

2. The evolved gas is passed through Nesslerʼs reagent which turns brown. This confi rms the presence of
ammonium ion in the salt mixture.

Chemical Reactions

1. NH +NaOH +

+
2
3
4 Na+ NH +H O
NH +HCl NH Cl
4
3 Densee white fumes

2. 2K HgI+ NH +3KOH → HN . HgO . HgI +7KI +2HO
2 4 3 2 2
or
I
Hg
O

Hg
NH 2
(Brown ppt.)

GROUP - I (Pb )
+2

If the original solution has been prepared in cold dilute HCl, Group I cations absent. In the present syllabus,
only Pb forms the Group I cation.
+2
To the original solution, add dilute HCl. Appearance of white ppt. indicates the presence of Group I cations.
Filter and retain the fi ltrate for subsequent groups. Take the precipitate in a test tube and boil it with water.
The precipitate gets dissolved and test with it in hot condition.

Confirmatory Test For Pb +2
Divide the hot solution in two parts:

1. Potassium iodine (KI) test: Add KI solution to the fi rst part. A yellow ppt. is formed which dissolves
on boiling.

2. Potassium chromate (K CrO ) test: To the second part, add K CrO solution. Yellow ppt. soluble in
2
4
4
2
NaOH is formed.
Chemical Reactions
Pb +2HCl PbCl +2H +
+2
2
W hite ppt.

1. KI test:
PbCl +2KI PbI +2KCl
2 2
Yellow ppt.

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