All living things contain a huge variety of different compounds. Nevertheless they consist of only a few elements, e.g. in dried peas you`ll find 46,5% carbon, 6,2% hydrogen, 40% oxygen, 4,2% nitrogen and 3,1% ash containing minerals.

Carbonization of organic compounds by heat

Required: 3 test-tubes, 1 -holder, BB, citric acid, glucose, peptone

Procedure:

Give one spatula of citric acid (or glucose or peptone) into a test-tube and heat.
Observations?
Which elements can be detected by this test?


Detection of nitrogen

Required: peas, a hard-fusing test-tube, -holder, indicator paper

Procedure:

A few dried peas are put into a test-tube and heated. If carbonization has already started hold a wet indicator paper into the vapour.
Observation? - Explanation?


Detection of sulphur I

Required: feathers, conc. NaOH, lead acetate-solution, t.-t. and -holder, BB

Procedure:

A piece of a feather is given into a test-tube and heated with a few [ml] of
conc. NaOH until it is dissolved. Add 5 drops of lead acetate-solution.
Observation?
Explanation: Pb²⁺ + S^2-  ———>  PbS (ppt)


Detection of sulphur II

Required: casein, KNO₃, dil. HCl, BaCl₂-solution, hard-fusing t.-t., -holder, filter

Procedure:

One spatula of casein is mixed in a test-tube with an excess (3times) of KNO3 and heated. If the nitrate is melted a vehement reaction starts. After reaction allow to cool and add ca. 10 [ml] aqua dest.; shake and filter.
Divide the filtrate into two portions. Acidify filtrate I and add a few drops of BaCl2-solution (filtrate II is used in the next experiment).
Observation?
Explanation: Ba²⁺ + SO₄^2-  ———>  BaSO₄ (ppt)


Detection of phosphorus

Required: conc. nitric acid, 10%-ammoniummolybdate-solution, filtrate II

Procedure:

Acidify filtrate II with conc. nitric , add ca. 2 [ml] of ammoniummolybdate-solution and warm (but do not boil).
Observations?
Explanation: The precipitate (ppt) is (NH₄)₃[P(Mo₃O₁₀)₄]