Tuesday, January 22, 2008

AIEEE Organic Chemistry UNIT 19B Qualitative and Quantitative Analysis


Qualitative analysis - detection of nitrogen, sulphur, phosphorus and halogens.
Quantitative analysis (basic principles only) – estimation of carbon, hydrogen, nitrogen, halogens, sulphur, phosphorus(basic principles only)
Calculations of empirical formula and molecular formula.
Numerical problems in organic quantitative analysis.


Detection of Elements (N,S, halogens)

Lassaigne test is used for this.

First sodium extract of the given organic compound is prepared.
A pea sized dry piece of sodium metal (freshly cut) is taken in an ignition tube and the tube is heated to melt the sodium metal piece to shining globule. Then a pinch of the organic compound is introduced in the tube. Then the tube is further heated first gently and strongly till the lower end of the tube becomes red hot. The tube is then plunged and broken in about 20 ml. of distilled water taken in porcelain dish. The solution is boiled for about 5 minutes and filtered. The filtrate obtained is known as sodium extract.

Test for Nitrogen

To 2ml of sodium extract, a little ferrous sulphate is added. The solution is boiled and a little dilute sulphuric acid is added. Appearance of prussian blue or green colouration indicates the presence of nitrogen in the compound.

Acetic acid and lead acetate are used for detecting sulphur and NH4OH is used for detecting halogens.

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