Background information and teacher's notes

This is very much a practical introduction to organic chemistry and is excellent for demonstrating (or reinforcing) the underlying theory. The aim is to familiarise students with some basic organic compounds and to get them to relate physical and chemical properties to particular functional groups. All of the functional groups are on the core in Topic 10 : Organic chemistry. The practical is also useful to help familiarise students with the IUPAC way of naming organic compounds.

All the reactions are small-scale test-tube type reactions. You may need to substitute some chemicals if you do not have the precise ones in stock but provided they contain the same functional groups this should make little difference. It may be the first time that students have handled organic compounds in the laboratory. They should be made aware that most are very volatile and also very flammable. They should avoid breathing in vapours as much as possible and if they need to heat the compounds it should be done using a water bath and never with a naked flame.

Adding water in experiment 1. simply demonstrates that the solubility of organic compounds in polar solvents such as water depends both on the polarity of the functional group and on the length of the carbon chain.

In terms of the chemistry it is worth reminding them about testing for unsaturation in experiment 2. Books just say add bromine water and observe if the bromine solution is decolourised. They should realise that they only need to add a small amount of bromine water i.e. the unsaturated compound should be in excess – sometimes students add far too much bromine water and are then surprised when it does not change colour. The reaction between hydrocarbons and halogens in sunlight is also on the core part of the programme under 10.2. Students should realise that saturated hydrocarbons can also decolourise bromine water but the reaction is much slower and needs the presence of ultra-violet light. If it is a sunny day then it takes about five minutes in bright sunlight for the reaction to work. Iron filings act as a halogen carrier and speed up the reaction between methylbenzene and bromine water. This could also be included if you wish but it is not required as an example of electrophilic substitution in 20.2. However it is much easier to do this practically than nitrate benzene, which is the example given.

Students need to know about weak acids and they should see that the solubility in water of organic acids such as benzoic acid increases dramatically when they are reacted with sodium hydroxide to form ionic salts. By deduction a similar effect is found when amines (which are weak bases) are reacted with acids to again form ionic salts. The chemistry of this is important for Option D: Medicinal chemistry. Many medicines (or illegal drugs) contain amine groups and are administered as their chloride salts - this is covered in more details in the page on salt formation under Novel uses for the IB data booklet. There are also good examples that are discussed in several of my blog pages including Plant food or drug?, Blue light cystoscopy, Applying IB chemistry to a diet pill and Tamoxifen as well as in a newspaper article on Shop until you pop.

The classification of alcohols into primary, secondary and tertiary and their response to mild oxidation is part of sub-topic 10.2. At SL students also need to be able to recognise the ester functional group and know the reaction between a carboxylic acid and an alcohol to make esters. It is fun for them to make an ester practically and smell the product (see right). After they have made ethyl ethanoate I get them to react a spatula full of salicylic acid (2-hydroxybenzoic acid) with a small amount of methanol in the same way (i.e. with a few drops of concentrated sulfuric acid acting as the catalyst). This will give them the very characteristic smell of methyl salicylate – which different cultures give different common names to. In the UK it is known as 'oil of wintergreen' and many students will recognise it as the smell of germolene or liniment to treat muscular pains

When they have finished the practical I briefly explain the chemistry behind the reactions. Then as we cover the chemistry in more detail in class I can refer back to these reactions and where necessary get them to write mechanisms as well as overall equations.