Chemistry F334 : What's in the Medicine

Topics: Carboxylic acid, Acetic acid, Alcohol Pages: 17 (2823 words) Published: February 6, 2012
What’s in a Medicine? (WM)
In this document you will find the following material to cover the new AS specification with your students. Notes for students and teachers Revised Chemical Ideas 13.4 part b Answers to problems for 13.4 part b Revised activity WM3 Answers to questions for revised activity WM3 Revised check your notes Revised map of the unit 2 3 6 7 9 10 11


© Harcourt Education Ltd 2004 Salters Advanced Chemistry These pages have been downloaded from


Notes for students and teachers
Chemical Storylines
At the end of WM3 on page 109: 1. Instead of Chemical Ideas 13.4 read 13.4 part b, which is available on the Heinemann website. 2. Read Section 13.5 in your Chemical Ideas book which deals with naming and making esters.

Chemical Ideas
1. While doing Chemical Ideas 13.5 there is no need to cover polyesters (page 318) or ester hydrolysis (page 319). These will be covered in Designer Polymers (DP). As a result there is no need to do Problems 4, 6 (parts d & e) or 8 (parts d & e). 2. Add Esters from salicylic acid (page 315). 3. Note that the anhydride reactions on pages 318–319 do not need to be learned. They are to explain activity WM5.1: A preparation of aspirin.

A revised version of activity WM3 investigates the chemistry of –OH groups. It is available on the Heinemann website.

End of unit test
Question 3 part e is not suitable for the new specification. (This work is now covered in The Polymer Revolution (PR).)


© Harcourt Education Ltd 2004 Salters Advanced Chemistry These pages have been downloaded from




The —OH group in alcohols, phenols and acids, part b
The hydroxyl group, —OH, can occur in three different environments in organic molecules: G attached to an alkane chain in alcohols, for example CH CH –OH 3 2 ethanol. Alcohols are of three types, primary, secondary and tertiary, according to the position of the OH group. You have already studied these in Section 13.4, part a. G

attached to a benzene ring in phenols, for example


(Although phenols look similar to alcohols they behave very differently. It is generally true that functional groups behave differently when attached to an aromatic ring from when they are attached to an alkyl group.) G

as part of a carboxyl group in carboxylic acids, for example O CH3 C OH ethanoic acid
For details on naming carboxylic acids see

section 13.3.

In this section we will compare the way the —OH group behaves in these three different kinds of compounds.

Acidic properties
The —OH group can react with water like this: R—OH + H2O


R—O– + H3O+

where R stands for the group of atoms which makes up the rest of the molecule (see Section 12.1). Water itself does this to a very small extent in the reaction H—OH + H2O


H—O– + H3O+

So, at any one time a small number of water molecules donate H+ ions to other water molecules: water behaves as a weak acid (see Section 8.1). A similar reaction occurs with ethanol, but to a lesser extent. The equilibrium lies further to the left, and ethanol is a weaker acid than water. With phenol, the equilibrium lies further to the right than in water: phenol is slightly more acidic than water. Carboxylic acids are even more acidic, though still weak. The order of acid strength is ethanol < water < phenol < carboxylic acids It is the stability of the R—O– ion formed from the acid which decides how strong the acid is, ie where the position of equilibrium lies. If the negative charge on the oxygen can be shared with other atoms, the R—O– ion will be more stable and more of it will be made. In the R—O– ion derived from alcohols, no such sharing is possible. However, in phenols and in carboxylic acids the electric charge gets spread out by a process called delocalisation. This involves a spreading out of the electrons over the...
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