In the name of God
Shahid Beheshti University
Faculty of Chemistry and Petroleum Sciences
2nd Semester
General Chemistry Laboratory 2
1403-2
title of the experiment:
Identification of group I cation
Experiment number: Experiment number 1
Name of the author of the work report: Amir Ahmadi
Collaborators Name: Amir Ahmadi, Sina Hosseini
Laboratory group number: No. 1
Date and time of the experiment: Sunday March 1st (Esfand 11th) 13:00-17:00
Field of study: applied chemistry
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Instructor Name: Dr. Soheila Naderi
Objective of the Experiment:
The objective of this experiment is to identify and separate Group I cations—specifically Pb²⁺, Hg₂²⁺,
and Ag⁺—using qualitative analysis techniques. Through selective precipitation, centrifugation, and
confirmatory reactions, the presence or absence of each ion is determined based on their unique
chemical behavior in acidic solutions.
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Used Tools:
Dropper, Distilled water, Paper towel, Test Tube, Heater, Beaker, Centrifuge, NH3 solution,
HCl solution, K2CrO4 solution, pipette
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Introduction:
Group I cation analysis is one of the most fundamental steps in qualitative inorganic analysis. It
involves identifying specific metal ions such as lead (Pb²⁺), mercury (Hg₂²⁺), and silver (Ag⁺), which
form insoluble chlorides in the presence of hydrochloric acid. This experiment uses precipitation
reactions, selective dissolution, and confirmatory tests to distinguish between these cations.
Through a step-by-step procedure involving heating, centrifugation, and reagent addition, each ion
can be detected based on its unique chemical behavior and color changes.
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Description of the experiment:
At first, 10 drops of the given solution (which may have one to three group I cations) is picked with a
dropper and poured into a test tube following by 10 drops of distilled water (is added to dilute the
solution).
Then 4 drops of HCl 6M is added to the test tube (be careful, if too much HCl is added, the insoluble
products of the reaction can become soluble again)
↓AgCl ⇾ AgCl2
↓PbCl2 ⇾ PbCl42The reason is that HCl is the common indicator of Ag+ Hg22+ Pb2+ ions. After that, the test tube is sunk
in a beaker of boiling water (for a few seconds) to increase the rate of precipitating.
Soon after, the warm tube is put in the centrifuge (make sure to put another tube with the same
weight in front of it to hold the balance of the spinning disk.). after its done the tube has to separate
part, the solution and the precipitate parts. In the precipitate part AgCl, Hg2Cl2 and PbCl2 might
exist; In the solution part, there might be a little Pb2+ ions left so its kept in another tube by pouring
it into another tube.
Now we have 2 tubes one with the solid particles (Tube No.1) and one which has the solution in it
(Tube No.2). about 3 drops of K2CrO4 solution is added to the 2nd tube and an eye-catching yellow is
appeared, it means that Pb2+ ions were present in the solution.
The first tube is picked and 6 drops of 4M NH3 is added to it also to increase the volume of the new
solution, a few drops of water is added. The reaction between ammonia and the precipitates:
Hg2Cl2 + 2NH3 ⇾ ↓Hg + Cl-Hg-NH2 + NH4+ + ClAgCl + 2NH3 ⇾ [Ag(NH3)2]+ + Cl- (H+)⇾ 2NH3 + ↓AgCl
Then the tube is put inside the centrifuge again and after its done we’ll have again a tube with solid
and liquid parts, the liquid part is poured in another tube.
The solid part has a gray color it means that Hg22+ ions were present in the given solution.
Then, 4 drops of HNO3 6M is added to the tube with the liquid part if a white precipitate (which is
AgCl) appears it means that Ag+ ions is present in the solution, but no precipitate was seen in the
experiment so it means that Ag+ ions were not present in the given solution.
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Conclusion:
The analysis of the given solution revealed the presence of Pb²⁺ and Hg₂²⁺ ions, confirmed by the
formation of yellow precipitate with K₂CrO₄ and a gray residue after reaction with ammonia,
respectively. No white precipitate was observed with nitric acid, indicating the absence of Ag⁺ ions.
The experiment successfully demonstrated the selective identification of Group I cations through
classic qualitative methods.