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Where are carboxylic acids found?


What are carboxylic acids?

Carboxylic acids contain a functional group of carbon, hydrogen and oxygen atoms arranged like this...

What do you think the carboxylic acid with three carbon atoms is called?

...which is written as –COOH.

methanoic acid (HCOOH) ethanoic acid (CH3COOH)

E.g.


Naming carboxylic acids


Making carboxylic acids

In fact, any carboxylic acid can be made by oxidizing the corresponding alcohol.

If you leave wine standing open to the air, oxygen from the air will oxidize the ethanol to ethanoic acid, forming vinegar.

Q) Which carboxylic acid is made when methanol is oxidized?A) Methanoic acid.

ethanoic acidoxygen waterethanol

+ +


Properties of carboxylic acids

Carboxylic acids:

have relatively high melting and boiling points

are very soluble in water

are weak acids

have a characteristic smell!

Examples of everyday carboxylic acids include:

citric acid (found in citrus fruits)

lactic acid (found in tired muscles)

malic acid (found in sour and tart foods).


Match the properties


Chemical properties of carboxylic acids

Carboxylic acids are typical weak acids.

What would happen if you added a few cm3 of dilute ethanoic acid to each of these substances?

A few drops of universal indicator.

3 cm3 sodium hydroxide solution.

Half a spatula of sodium carbonate.

A piece of magnesium ribbon.


Reactions of carboxylic acids



Carboxylic acids react like any other type of acid, forming salts when they react with alkalis, carbonates and metals:

ethanoic acidsodium

ethanoatewatersodium

carbonate+ +

carbondioxide

+

2CH3COOH 2CH3COONa H2ONa2CO3+ +CO2+

ethanoic acidsodium

ethanoatehydrogensodium+ +

2CH3COOH 2CH3COONa H22Na+ +

ethanoic acidsodium

ethanoatewater

sodiumhydroxide

+ +

CH3COOH CH3COONa H2ONaOH+ +


Carboxylic acids in descalers

In hard water areas, limescale (calcium carbonate) builds up in kettles and water pipes.

To remove the limescale, a descaler can be used, which contains ethanoic acid.

What reaction takes place between the ethanoic acid and limescale?

ethanoic acidcalcium

ethanoatewater

calciumcarbonate

+ +carbondioxide

+

2CH3COOH (CH3COO)2Ca H2OCaCO3+ +CO2+


Carboxylic acids in soaps

Fatty acids are carboxylic acids with very long carbon chains.

The sodium and potassium salts of fatty acids can be used as soaps.

For example, reacting octadecanoic acid with sodium hydroxide produces sodium octadecanoate, a common soap.

+

(octadecanoic acid)

+

(sodium octadecanoate)


Carboxylic acids: summary


What are esters?

Esters have characteristic smells, and are often used in flavourings and perfumes.

For example:

propyl ethanoate smells of pears

butyl butanoate smells of pineapple

methyl butanoate smells of apple.


Esters

Esters contain this group of atoms:

Esters are made from the reaction of a carboxylic acid with an alcohol:

...which is written as –COO–.

carboxylic acid + alcohol ester + water

+ +

+ +CH3CH2COOH CH3OH H2OCH3CH2COOCH3

propanoic acid methanol methyl propanoate water+ +


Naming esters

Esters are named after the alcohol and the carboxylic acid from which they are made. The alcohol gives the first part of the name, and the carboxylic acid gives the second. Esters always end in “–anoate”.

ethanoic acid methanol

methyl ethanoate

For example:


Matching carboxylic acids to their esters


Practising naming esters


How are esters made?

Esters are made by reacting a carboxylic acid with an alcohol.

How could you speed it up?

The reactants could be heated in order to make the reaction faster.

A catalyst of concentrated sulfuric acid could be added.

However, the reaction is very slow at room temperature.


Making esters


What are the stages in making an ester?


Glossary


Anagrams


Multiple-choice quiz

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