1. Carboxylic Acids
All carboxylic acids are characterised by the presence of the carboxyl group as shown.

2. Naming Carboxylic Acids
Names are derived from the number of carbons in the chain.
The ‘e’ of an alkane is replaced by the suffix ‘oic acid’.
The carboxyl carbon atom in the COOH functional group is ALWAYS numbered carbon 1.
Branches on chains are always on the lowest number carbon possible, starting with the carboxyl carbon.

3. Structures of methanoic and ethanoic acids
Week 4
Structures of methanoic and ethanoic acids
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4. Structure of 4-methylhexanoic acid
Week 4
Structure of 4-methylhexanoic acid
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5. Naming Exercise Draw displayed structures and name the following:
CH3CH2COOH
C6H5COOH
ClCH2COOH
HOOCCH2COOH
Propanoic acid
Benzoic acid
Chloroethanoic acid
Propane-1,3-dioic acid

6. More naming practise
Complete question 1a,b and c from p. 29 in OCR Chemistry
Draw the following:
2-hydroxypropanoic acid
3-methylbenzoic acid.
Benzene-1,4-dicarboxylic acid
3-methylbutanoic acid

7. Explain the water solubility of carboxylic acids.
Week 4
Explain the water solubility of carboxylic acids.
Describe the reactions of carboxylic acids with metals, carbonates and bases.
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8. Physical Properties of Carboxylic Acids
All carboxylic acids are either liquids or solids.
MP and BP increase with increasing chain length.
The first 4 carboxylic acids are soluble in water but solubility decreases with increasing chain length.
Why?
Hydrogen bonding explains it all.

9. More naming practise Boiling Points of first 4 carboxylic acids. Acid
Formula
BP/oC
Methanoic acid
HCOOH
110.5
Ethanoic acid
CH3COOH
118
Propanoic acid
CH3CH2COOH
141
Butanoic acid
CH3CH2CH2COOH
163

10. Hydrogen Bonding
Each acid is capable of forming 2 hydrogen bonds per molecule. (Shown as thin lines)
These increase intermolecular forces so that more energy than expected is needed to separate the molecules than if simple Van der Waal’s forces only were present.

11. Hydrogen bonds, strong dipole–dipole interactions
Week 4
Hydrogen bonds, strong dipole–dipole interactions
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12. Solubility
Hydrogen bonding also accounts for the solubility of carboxylic acids.
As the chain length increases the solubility decreases as a result of the increasing non polar chain which cannot interact with water molecules and doesn’t disrupt the hydrogen bonds between water molecules.

13. Reactions of Carboxylic Acids
Carboxylic acids are WEAK compared with the mineral acids, nitric sulphuric etc.
Why are they weak acids?
They do however behave as typical acids reacting with metals, metal oxides, metal hydroxides and metal carbonates to from salts containing the carboxylate anion.

14. Week 4 Carboxylate ion 14 © Pearson Education Ltd 2009
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15. Weak Acids?
Mineral acids are strong acids – they ionise completely in water.
HCl + H2O → H3O+ + Cl-
Carboxylic acids only partly dissociate in water:
CH3COOH + H2O D CH3COO- + H3O+
This is because the carboxylate anion is a strong base, strengthened by the +I effect of the chain, increasing electron density on the O of the OH group, strengthening the OH bond and making the ethanoate ion more likely to attract an H+ ion back, should it be lost.

16. Reactions of Carboxylic Acids: Complete the Spider Diagram
Salt + water
Salt + Hydrogen
Acid
Salt + water
Salt ,water + carbon dioxide