2. Qualitative Analysis
• A qualitative characteristic is a
description of something that does not
involve numbers or units of measurement.
• We will try to identify a substances using
characteristic such as colour and
solubility.
3. Ion Colour
• The colour of substances can
sometimes be used to identify ions
or compounds within the substance.
• See page 665
4. CHEMISTRY CSI
• You can also use the
solubility rules to
determine the presence
of certain ions in a
solution .
• Mix your sample that
contains the suspected
ion with a solution that
contains an ion that will
form a precipitate with
your suspect ion.
• Take advantage of the
net ionic equation.
5. EXAMPLE 1
• Lets say you suspect your water sample
has acetate in it. What could you do?
• If you combine your water sample with a
solution that contains silver ions (Ag+
) or
mercury ions (Hg+
) a precipitate will form.
• silver acetate/mercury acetate will form
which is insoluble – meaning it will form a
precipitate.
Hg+
(aq) + C2H3O2
-
(aq) HgC2H3O2 (s)
Ag+
(aq) + C2H3O2
-
(aq) AgC2H3O2 (s)
6. THE BIG PROBLEM
• The major issue that has to be dealt
with is that most solutions or
samples contain more than one type
of ion so chemists must design test
procedures to identify and remove
any suspected ions one at a time…
• You need to find a solution that will
react (form a precipitate) with only
one of the ions at a time.
7. EXAMPLE 2
• Lets say we suspect a solution has both
iron (Fe2+
) and strontium (Sr2+
) ions in it.
• Solubility rules say that hydroxide ions
(OH-
) will react with the iron ions (Fe2+
)
and form a precipitate but will not have
the same reaction with strontium ions.
• We could also use a solution containing
sulphate (SO4
2-
)since it will react with the
strontium and not the iron.
Fe2+
(aq) + OH-
(aq) Fe(OH)2(s)
Sr2+
(aq) + SO4
-2
(aq) SrSO4(s)
8. EXAMPLE 2…Part 2
• To remove the compound from the
solution we will filter the solution with the
precipitate. The solid compound will be
trapped by the filter paper.
• The solution passing through the filter
paper is called the filtrate and will contain
the unreacted ions. We keep this for
further testing.
9. EXAMPLE 2…Part 3
• Now we have the filtrate with the
unreacted ions in it…how do we test for
the ions?
• As before use the appropriate ion to
cause precipitation.
10. Practice Problem
• How would you determine if a solution
contains ions of silver Ag1+
(aq) and/or ions of
zinc, Zn2+
(aq) ?
• Chloride Cl1-
and sulphate SO4
2-
ions
precipitate silver but not zinc.
• Add a source of either ion, if a precipitate
forms the solution contained silver ions. If
no precipitate forms, silver ions were not
present.
Ag1+
(aq) + Cl1-
(aq)→ AgCl(s)
• Filter out the solid if a positive test.
11. Practice Problem Cont.
• Find an ion that will precipitate out
Zn2+
(aq)
• Any ion from the bottom of the
solubility table will precipitate out
Zn2+
(aq) ie. hydroxide ions OH1-
(aq)
• Add a source of the ion and check
for precipitation. ppt = ion present,
no ppt = ion not present.
Zn2+
(aq) + 2OH1-
(aq) → Zn(OH)2(s)
12. Practice
• Devise a method to determine if a
solution contains the following ions.
– strontium and/or manganese2+
– copper+1
and/or iron3+
– hydroxide and/or acetate
14. Flame Test For Cations
• The flame test is a procedure used in
chemistry to detect the presence of
certain metal ions, based on each element's
characteristic emission spectrum. The color
of flames in general also depends on
temperature.
• The flame test is fast and easy to perform,
and does not require special. However, the
range of detected elements is small, and
the test relies on the subjective
experience of the experimenter rather
than any objective measurements.
15. Flame Tests
• The test involves
introducing a sample of
the element or compound
to a hot, non-luminous
(blue) bunsen flame, and
observing the color that
results.
Samples are usually held on a nichrome wire
cleaned with hydrochloric acid to remove
traces of previous analytes.
16. Flame Tests
Potassium - Purple Sodium - Yellow Barium - Green
Sodium is a common component or contaminant in
many compounds and its spectrum tends to dominate
over others. Thus the color yellow overpowers the
true color.
The test flame is often viewed through cobalt blue
glass to filter out the yellow of sodium and allow for
easier viewing of other metal ions.
17. Flame Colours
• As Arsenic - Blue
• B Boron - Bright Green
• *Ba Barium - Apple
Green
• Ca Calcium - Brick Red
• Cs Cesium - Pale Violet
• Cu(I) Copper(I) - Blue
• Cu(II) Copper(II) (non-
halide) - Green
• *Cu(II) Copper(II)
(halide) -Blue-Green
• *Fe Iron - Gold
• In Indium - Blue
• *K Potassium - Lilac
• Li Lithium – Carmine Red
Mg Magnesium - Brilliant white
Mn(II) Manganese(II) –
Yellowish green
Mo Molybdenum - Yellowish
green
*Na Sodium - Intense Yellow
P Phosphorus - Pale bluish green
Pb Lead - Pale green
Rb Rubidium - Pale violet
Sb Antimony - Pale green
Se Selenium - Azure blue
Sr Strontium - Crimson Red
Te Tellurium - Pale green
Tl Thallium - Pure green
Zn Zinc - Bluish Green
