Page 66 - Chemistry - XI

2. K CrO test:
4
2
PbCl +K CrO PbCrO +2KCl
2 2 4 4
Yellow pppt.

PbCrO+ 2NaOH NaCrO +PbOH
4 2 4 2
S oluble

FLOW CHART FOR ANALYSIS OF GROUP - I

Original Solution (O.S.)

Dil. HCl

Precipitate No precipitate
Group I present Group I absent

Filter
Proceed for
White ppt. analysis of

Group II to VI
Boil with water and
divide into two parts

First part Second part

KI solution K CrO solution
2 4
Yellow ppt. soluble in
Yellow ppt.
NaOH solution

Pb confi rmed
+2

GROUP - II (Pb , Cu )
+2
+2
According to the present syllabus, only Pb and Cu constitute the Group II radicals. They are precipitated
+2
+2
as sulphides by H S in presence of dilute HCl.
2
Now take about 2 mL of the fi ltrate of Group I or if Group I is absent, take about 2 mL of original solution,
acidifi ed with dilute HCl and pass H S gas into it. The formation of black coloured ppt. indicates the
2
presence of second group. Filter it and proceed as follows:

Black precipitate for Cu and Pb : Wash the black precipitate with hot distilled water and boil withBlack precipitate for Cu +2 +2
10 mL of 50% nitric acid. The precipitate gets dissolved.10 mL of 50% nitric acid. The precipitate gets dissolved.

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