Page 77 - Lab Manual & Project class 12

SYSTEMATIC QUALITATIVE ANALYSIS
the presence of group-IV cations. Table 7.15 gives a summary of confirmatory
tests of group-IV cations.

Table 7.15 : Confirmatory test for Group-IV cations

White precipitate Flesh coloured precipitate Black precipitate
2+
2+
2+
2+
(Zn ) (Mn ) (Ni , Co )
Dissolve the precipitate Dissolve the precipitate in Dissolve the precipitate in
in dilute HCl by boiling. dilute HCl by boiling, then add aqua regia. Heat the
Divide the solution into sodium hydroxide solution in solution to dryness and
two parts. excess. A white precipitate is cool. Dissolve the residue
formed which turns brown on in water and divide the
(a) To the first part add keeping. solution into two parts.
Maxbrain Chemistry
sodium hydroxide
solution. A white (a) To the first part of the
precipitate soluble solution add ammonium
in excess of sodium hydroxide solution till it
hydroxide solution becomes alkaline. Add
confirms the a few drops of dimethyl
presence of Zn 2+ glyoxime and shake the
ions. test tube. Formation of
a bright red precipitate
(b) Neutralise the confirms the presence
second part with of Ni ions.
2+
a m m o n i u m
hydroxide solution (b) Neutralise the second
and add potassium part with ammonium
f e r r o c y a n i d e hydroxide solution.
solution. A bluish Acidify it with dilute
white precipitate acetic acid and add
appears. solid potassium nitrite.
A yellow precipitate
confirms the presence
2+
of Co ions.

Chemistry of confirmatory tests of Group–IV cations

Fourth group cations are precipitated as their sulphides. Observe the colour of
the precipitate. A white colour of the precipitate indicates the presence of zinc
ions, a flesh colour indicates the presence of manganese ions and a black colour
2+
2+
indicates the presence of Ni or Co ions.
2+
1. Test for Zinc ion (Zn )
Zinc sulphide dissolves in hydrochloric acid to form zinc chloride.
ZnS + 2HCl ZnCl + H S
2
2
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24-04-2018