Below is the experiment
Experiment 8: Identification of metal ions and
inorganic compounds in aqueous solution
Introduction:
Inorganic qualitative
analysis is the unambiguous identification of cations and anions present in the
solutions. The techniques used in qualitative analysis can be vary in
complexity, depending on the nature of the samples. (Encyclopeadia Britannica
2014) Unique tests for all ions in the possible presence of all others are
virtually impossible to devise because different cations give similar results
to each other. Therefore, a solution is treated to separate ions into smaller
groups to identify the metal ions.
Next,
selective precipitation is the most common way to subdivide cations into
smaller groups, in which a small group of cations is precipitated chemically.
The precipitate formed can be separated physically from the remaining cations
in the solution by centrifuging. The precipitate which is the insoluble solid
settles out and the solution (supernatant liquid) is decanted into another
container. As a result, the initial large group can be divided into smaller
groups until a definitive test can be performed to verify the presence or
absence of each specific cation.
Besides,
it is important to know that many chemical reactions do not go to completion.
The difference to which a reaction occurs depends on the magnitude of the
equilibrium constant,
In
this experiment, various types of reagents are used so that the precipitation
presents. The techniques stated above are used in order to identify the metal
ion present in an unknown solution. It is also employed to identify an unknown
inorganic compound in this experiment by observing the colour changes of the
solution when it reacts with other reagents. The reagents are dissolved
sparingly so that the soluble compounds or complex particular ions will not
interfere with tests for other ions.
Objective:
To identify the
inorganic compounds by their chemical reactions.
Apparatus Needed:
Test tubes, droppers
Chemicals Needed:
0.1M Ba (NO3)2 solution, 0.1M Mg(NO3)2
solution, 0.1M Pb(NO3)2
solution, 0.1M Co(NO3)2 solution, 0.1M Fe(NO3)3 solution, 0.5M (NH4)2SO4, 0.5M NH4SCN, 0.5M NaOH solution, 4M NaOH solution, 0.5M NH3(aq) solution, 4M NH3(aq) solution, 0.5 M CuSO4 solution, 0.5M Pb(NO3)2 solution, 0.5M Zn(NO3)2 solution, 0.5 M BaCl2
Procedures:
A. Identification of
metal ions in aqueous solution
1.
Five dry test tubes were obtained. The test tubes
1,
2, 3, 4 and 5 were labelled.
2.
Four drops of 0.1 M Ba (NO3)2 solution was
added to test tube 1, four drops of 0.1M Mg (NO3)2
solution was added to test tube 2, four drops of 0.1 M Pb (NO3)2
solution was added to test tube 3, four drops of 0.1 M Co (NO3)2
solution was added to test tube 4, and
four drops of 0.1M
Fe (NO3)3
solution was added to test tube 5.
3.
The color of the metal ion solution in each test tube was
recorded in the results
section.
4.
Four drops of 0.5M (NH4)2SO4 were added to each of the five test tube in step 2.The test tube was
carefully observed for any evidence of reaction. The
observations were recorded in the table on the results section. The formulas of the substances formed in this
reaction were written in the results section. If no reaction occurs, ‘no change, NC’
was written.
5.
The contents of the five test tubes
were emptied into the waste container.
6.
Steps 1 and 2 above were repeated, four drops of each metal nitrate
solution
was added to separate clean, dry test tubes.
7.
Four drops of 0.5M NH4SCN was added to each of the five test tubes from steps 6.The test tubes
were carefully observed for any evidence of reaction. The observations
were recorded in the table on the data sheet. The contents of the five
test
tubes were emptied into the waste container.
8.
Steps 1 and 2 were
repeated, four drops of each metal nitrate solution were added to separate clean, dry test tubes.
9.
Four drops of the freshly prepared 0.5M NaOH solution (limited OH- ions) was added to each of the five test tubes in step 8. The test tubes
were carefully observed for any reaction. The observations were recorded in the results section.
The
contents of the five test tubes were emptied into the waste container.
10. Steps 1 and 2
were repeated, four drops of each metal nitrate solution were added to separate clean, dry tubes.
11.
Four drops of 4M NaOH solution (excess OH- ions) were
added to each of the five test tubes in step 10. The test tubes
were carefully observed for any evidence of reaction. The observations
were recorded in the
results section.
The contents of the five test tubes
were emptied into the waste container.
12.
Steps 1 and 2 were
repeated, four drops of each metal nitrate solution was added to separate clean, dry test tubes.
13. Four drops of the freshly prepared 0.5M NH3(aq) solution
were added to each of
the
five test
tubes in step 12.
The
test tubes
were carefully observed for any evidence of reaction.
The observations were recorded on the data sheet. The contents of the five test tubes
were emptied into the waste container.
14. Steps 1 and 2 were
repeated, four drops of each metal nitrate solution were added to separate clean, dry test tubes.
15. Four drops of 4M of NH3(aq) solution
was added to each of the five test tubes in step 14. The test tubes were carefully observed for any evidence of reaction. The
observations were recorded in the table in the results section. The contents of the five test tubes were emptied into the waste container.
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