Chem 3 - Analysis - Tests for Organic Substances

From the earliest days of science people have heated substances to see what happened to them. Two hundred years ago a Swedish chemist called Jons Jakob Berzelius decided that chemicals could be classed into 2 groups according to how they behaved when heated.

Chemicals that burned or charred on heating came mainly from living things, so Berzelius called these Organic Subtances.

In contrast, other substances melted or vapourised when Berzelius heated them. These returned to their orginal state when cooled. Berzelius called these Inorganic Substances.

Our modern definition describes Organic chemicals as substances which are based on the element Carbon.

Unsaturated Hydrocarbons will react with Bromine water, producing colourless compounds. This is a good way of testing a Hydrocarbon to see if it contains a Carbon-Carbon double bond.

This test is the basis for determining the number of Carbon-Carbon double bonds in unsaturated oils and fats. The oil is titrated against an Iodine solution. The Iodine number of the fat is based on the number of molecules of Iodine needed to react with all of the Carbon-Carbon double bonds in one molecule of the fat.