This document outlines qualitative tests for carbon, hydrogen, oxygen, nitrogen, halogens, and sulfur in organic compounds. Carbon and hydrogen are detected by heating compounds with CuO and observing the formation of calcium carbonate and water droplets. Oxygen is detected using ferrox paper or iron(III) hexathiocyanatoferrate(III) solutions, which turn red in the presence of oxygen. Nitrogen, halogens, and sulfur require sodium fusion to convert them to inorganic ions before qualitative testing, such as using Prussian blue for nitrogen or lead sulfide for sulfur.

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.