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Qualitative organic analysis

The first steps in the identification of organic compounds are based upon physical tests. These include appearance, color, odor, and solubility. These tests are followed by deter­mining either the melting point (of solid sub­stances) or the boiling point (of liquids). By comparing these results with those in pub­lished tables, the analyst can rapidly narrow down the number of chemical possibilities. Further identification then follows a well-established procedure. The elements present in the compound are determined by decom­posing it into inorganic substances. It is then established whether the compound is an


 


Flame testscan reveal the presence of various metals. A sample (preferably a chlo­ride) is burned in a Bunsen flame on a platinum wire. The color of the flame iden­tifies the metal. Na = so­dium; Li = lithium; Sr = strontium; Ca = calcium; K = potassium; Ba = barium; Cu = copper; Pb = lead.


 

                ■' ■■ '..■ ■: ■
I                          
Na Lij   Sf Ca   K   Ba   Cu   Pb   K + Na


Analytical chemistry: Classical analysis 1Z9



Mixture containing up to 22 different metals
Add HCI

0®@(^
Silver, mercury and lead as chlorides

Arsenic, bismuth, cadmium, copper, antimony and tin as sulfides

Al^rYF. Aluminum, chromium, iron and manganese as hydroxides

(an Cobalt, nickel and zinc as sulfides

Add (NH4)2CO ______ Is

*3& Barium, calcium and strontium as carbonates


acidic, alkaline, or neutral substance. Acids and alkalis are discussed in the article "Key chemical reactions" in the beginning of this book.

The preceding process is followed by a se­ries of tests to determine the nature of the re­active groups in the compound. The tests are carried out on very small quantities of mate­rial. Many of these tests give rise to colored precipitates or solutions when a positive result is obtained. Once the substance has been pro­visionally identified, it may be confirmed by using one of a variety of other tests.


Date: 2015-12-11; view: 225


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