CHEMISTRY

1. QUALITATIVE TESTS FOR ELEMENTS IN
ORGANIC COMPOUNDS

2. Carbon and hydrogen
•
Detected qualitatively by a heating a mixture
(glucose) with dry CuO in a test tube.
•
The glucose is oxidized forming CO2 and H2O.
•
The presence of CO2 is indicated by the
formation of a white ppt. of calcium
carbonate when gaseous products are passed
through a solution of lime water.
•
The presence of water is indicated by the
formation of droplets of water in the cooler
end of the hard glass tube.

3. Oxygen
•
The presence of oxygen may be determined
either with the use of ferrox paper or the
compound iron (III)
hexathiocyanatoferrate(III).
•
In the presence of oxygen contaning
compounds, the complex FeCNS++
gives a deep
red colored solution as it distributed between
the filter paper and the test compound.

4. •
Solutions of compounds which do not contain
oxygen remain colorless.
•
Iron (III) ammonium sulfate and potassium
thiocyanate react to form iron (III)
hexathiocyanatoferrate(III). This compound
dissolves in the presence of oxygen-containing
compounds to give a red to reddish-purple
color.

5. •
2Fe(NH4)(SO4)2 + 6 KSCN
Iron (III) ammonium sulfate potassium thiocyanate
Fe[Fe(SCN)6] + 3 K2SO4 + (NH4)2SO4
iron (III) hexathiocyanatoferrate(III)

6. Nitrogen, Halogens and Sulfur
•
Difficult to detect for organic compounds due
to its non-polar nature. They do not ionize in
solution to give ions.
•
Necessary to convert these elements into
inorganic ions before making qualitative tests.
•
The conversion is done through fusion with
metallic sodium, w/c decomposes the organic
compound forming soluble salts.

7. •
Organic compound [C] [H][O][N][X][S] + N
fusion
NaCN, NaOH, NaX and Na2S
The resulting organic compounds are tested
qualitatively for the presence of N, S and
halogens.

8. NITROGEN
•
Detected by the formation of Prussian blue
after the sodium fusion.
•
Nitrogen in cyanide form is converted to
sodium ferrocyanide, which produces Prussian
blue (ferric ferrocyanide, Fe4[Fe(CN)6]3 with
ferric chloride in acid solution.
•
Nitrogen in the form of amino nitrogen (-NH2),
heating with soda lime (a mixture of fused
NaOH and CaO) will liberate ammonia gas,
which is tested with moist red litmus paper.

9. Sulfur
•
Detected by the production of brownish-black
lead sulfide.
•
With sodium nitroprusside, the sulfide ion
produces a red-violet color, which fades
somewhat readily.

10. Halogens
•
Detected by Beilstein test.
•
Organic halogen imparts a green color to the
flame when burned upon the surface of a
copper wire. The copper oxide formed from
the copper wire reacts with the halogens to
form the cuprous halide, which burns with a
green flame.