Chemistry F334 : What's in the Medicine

2814 Words Jan 28th, 2012 12 Pages
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

WM

© Harcourt Education Ltd 2004 Salters Advanced Chemistry These pages have been downloaded from www.heinemann.co.uk/science

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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
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Phenols and carboxylic acids are strong enough acids to react with strong bases, such as sodium hydroxide, to form salts. For example,
OH Na+OH− O− Na+

+

+

H2O

phenol

sodium phenoxide

O CH3 C OH ethanoic acid + Na+OH— CH3 C

O + O− Na+ sodium ethanoate H2O

Only with solutions of carboxylic acids is the concentration of H+(aq) ions great enough to give carbon dioxide when reacted with carbonates. (Note that the H3O+ ion is often written as H+(aq).) CO32–(aq) + 2H+(aq) → CO2(g) + H2O(l) So carboxylic acids make carbonates fizz, but alcohols and phenols do not.

To summarise
G G

G

Carboxylic acids and phenols react with NaOH(aq) to form their sodium salts. Carboxylic acids, but not phenols, react with Na2CO3(aq), with fizzing and release of carbon dioxide, to form the sodium salt of the acid. Alcohols do not react with either NaOH(aq) or Na2CO3(aq).

The iron(III) chloride test
Some groupings of atoms can become closely associated with metal ions and form complexes (an example you have met is the dark blue complex which ammonia forms with Cu2+ ions). The C=C— OH group (it is called the ‘enol’ group, can you see why?) can form a purple complex with Fe3+ ions in neutral solution. Only phenol and its derivatives have such an arrangement and are the only ones to give a colour with iron(III) chloride.
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