University of Santo Tomas-Legazpi
COLLEGE OF HEALTH SCIENCES
Rawis, Legazpi City
EXPERIMENT 2: QUALITATIVE ANALYSIS OF CATION GROUP 2 - HYDROGEN
SULFIDE GROUP
I.
INTRODUCTION
The identification of the different ions contained in a sample is a typical task in analytical chemistry.
Qualitative analysis is a frequent experimental approach for identifying ions in a mixture. The ions in a mixture
are separated by selective precipitation in qualitative analysis. The addition of a carefully chosen reagent to
an aqueous mixture of ions results in the precipitation of one or more of the ions while leaving the rest in
solution.
II.
METHODOLOGY
The preparation of the known solution was done by mixing 2 drops each of Bi 3+, Cu2+, Sb3+ in a test
tube. The solution was then tested for its acidity by using the universal indicator paper. Since the prepared
solution was tested acidic, the student then proceeded to add 2 drops of 13% thioacetamide in the solution
and subjected the test tube in a warm water bath to initiate its chemical reaction. As the solution was being
heated, black precipitate starts to form. Once the solution has turned a darker color, it was then centrifuged.
After the solution was centrifuged, the supernatant was then collected to a new test tube by decantation. The
collected supernatant was added with 2 drops of 13% thioacetamide to test if complete dissolution occurred.
The solution was placed in the warm water bath once more, and precipitates began to form after a few
minutes, suggesting that full dissolution had not occurred. The test was done 4 times by the student. Once
the solution reached complete dissolution, the student then proceeded to rinse the collected precipitates in
each test tube by adding 6M of NH4HCl and 20 drops of hot water. The solutions containing the precipitates
were combined into one test tube and then centrifuged. After centrifugation, the supernatant was discarded,
leaving the black precipitates at the bottom of the test tube.
University of Santo Tomas-Legazpi
COLLEGE OF HEALTH SCIENCES
Rawis, Legazpi City
The collected precipitate was then added with 10 drops of 0.5M KOH and was heated in a warm
water bath. After being subjected to a warm water bath, it was centrifuged. The supernatant was then
collected to a new test tube.
III.
RESULTS AND DISCUSSION
In the experiment, Group II ions are separated by precipitating their insoluble sulfides. The sulfide
ion is produced by the weak electrolyte gaseous hydrogen sulfide, which is only very slightly soluble in water.
Hydrogen sulfide is created when thioacetamide undergoes hydrolysis.
This reaction is catalyzed by the acidity of the solution and heat when subjected to the warm water
bath. This ideal way of producing hydrogen sulfide is used to reduce the escape of the very dangerous and
foul smelling gas into the environment, as well as to encourage the creation of purer, coarser, and more
conveniently handled sulfide precipitates.
Due to time restrictions, the test for the Group II cations was shortened during the experiment. It
ended with the addition of KOH in the precipitate.
University of Santo Tomas-Legazpi
COLLEGE OF HEALTH SCIENCES
Rawis, Legazpi City
EXPERIMENT 2: QUALITATIVE ANALYSIS OF
CATION GROUP 2 - HYDROGEN SULFIDE
GROUP
(LABORATORY REPORT)
JOSE CARLOS BINOS
1BSMT1