Carboxylic Acids and Esters

Question 1

What is the functional group of carboxylic acids?

Answer 1

Question 2

What are the names and structural formulae of the first four carboxylic acids?

Answer 2

• Methanoic acid - HCOOH
• Ethanoic acid - CH₃COOH
• Propanoic acid - CH₃CH₂COOH
• Butanoic acid - CH₃CH₂CH₂COOH

Question 3

What is the general formula of carboxylic acids?

Answer 3

CₙH₂ₙ₊₁COOH

Note that this does not apply to methanoic acid

Question 4

What is the displayed formula of methanoic acid?

Answer 4

Question 5

What is the displayed formula of ethanoic acid?

Answer 5

The displayed formuale of propanoic and butanoic acid follow a logical progression

Question 6

What is vinegar?

Answer 6

An aqueous solution of ethanoic acid with the volume consisting of 5% ethanoic acid

Question 7

What happens when a carboxylic acid reacts with a metal?

Answer 7

• They react with metals to form a salt and hydrogen just like other acids
• For example: Ethanoic acid + magnesium –> magnesium ethanoate + hydrogen

Question 8

What happens when a carboxylic acid reacts with a metal oxide?

Answer 8

• They react with metals to form a salt and water just like other acids
• For example: Ethanoic acid + magnesium oxide –> magnesium ethanoate + water

• This is of course a neutralisation reaction
• As you should know, a similar thing will happen when reacting with metal hydroxides

Question 9

What happens when a carboxylic acid reacts with a metal carbonate?

Answer 9

• They react with metals to form a salt, water and carbon dioxide just like other acids
• For example: Ethanoic acid + magnesium carbonate –> magnesium ethanoate + water + carbon dioxide

Question 10

What is the equation for the reaction between propanoic acid and sodium hydroxide (as an example)?

Answer 10

CH₃CH₂COOH + NaOH –> CH₃CH₂COONa + H₂O

You can see that the metal displaces the hydrogen on the end of the functional group

Question 11

What is the functional group of esters?

Answer 11

Question 12

How are esters formed?

Answer 12

• Alcohols and carboxylic acids are reacted
• This is in the presence of a concentrated acid catalyst (such as sulfuric acid)
• The ester, along with water is produced

This is known as an esterification reaction

Question 13

How are esters named?

Answer 13

• The prefix of the alcohol used has ‘yl’ added to it
• This is followed by the prefix of the carboxylic acid with ‘oate’ added to it
• For example, if pentanol and methanoic acid are reacted together, pentyl methanoate will form

Question 14

What is the displayed formula of ethyl ethanoate (as an example)?

Answer 14

• The carboxylic acid section is first, followed by the alcohol section
• You can see that, when reacting, the carboxylic acid loses the OH on its functional group, and the alcohol loses the H on its functional group

Question 15

What is the displayed formula of methyl butanoate (as another example)?

Answer 15

Question 16

What is the reaction between ethanoic acid and ethanol with the balanced chemical equation?

Answer 16

• Ethanol + ethanoic acid –> ethyl ethanoate + water
• C₂H₅OH + CH₃COOH –> CH₃COOC₂H₅ + H₂O

The reaction happens in the presence of a concentrated sulfuric acid catalyst

Question 17

What are the general properties of esters and what are they therefore used for?

Answer 17

• Sweet, strong and distinct smelling
• Volatile (easily evaporating)
• They are therefore used as perfumes and sometimes as food flavourings

Question 18

Describe an experiment to prepare ethyl ethanoate

Answer 18

• Mix ethanoic acid, ethanol and concentrated sulfuric acid and heat it with an electric heater
• The ester is then distilled off and collected through condensation (this is easy as it has a low boiling point and is volatile)
• Sodium carbonate can be added to the final solution to remove acidic impurities, and calcium chloride to remove alcoholic impurities