AQA GCSE Chemistry Foundation (8462), Foundation tier · Organic chemistry › Reactions of alkenes and alcohols
Practise Carboxylic acids. 5 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Carboxylic acids: the –COOH functional group, the first four acids, their reactions with carbonates, in water and with alcohols to make esters. GCSE Chemistry only. Expect naming, observations, word equations and ester questions.
Carboxylic acid + carbonate → salt + water + carbon dioxide (fizzing)
Salts end in -oate, e.g. sodium ethanoate
Carboxylic acid + alcohol → ester + water (acid catalyst)
Ethanoic acid + ethanol → ethyl ethanoate + water
Ester group: –COO–
Notes
The carboxylic acids
diagram
Carboxylic acids contain the –COOH functional group.
The first four: methanoic acid HCOOH, ethanoic acid CH3COOH, propanoic acid CH3CH2COOH and butanoic acid CH3CH2CH2COOH.
The carbon atom in –COOH counts in the name: ethanoic acid has two carbon atoms in total.
Ethanoic acid:
Vinegar is a dilute solution of ethanoic acid.
Reactions
diagram
With carbonates: fizzing, as carbon dioxide is given off (it turns limewater milky). A salt and water also form: ethanoic acid + sodium carbonate → sodium ethanoate + water + carbon dioxide.
The salts end in -oate: methanoate, ethanoate, propanoate, butanoate.
In water: they dissolve to form acidic solutions (pH below 7).
With alcohols: with an acid catalyst (e.g. concentrated sulfuric acid), they react to form an ester and water: ethanoic acid + ethanol → ethyl ethanoate + water.
Esters contain the –COO– group. Ethyl ethanoate is the only ester you need to name.
Ethyl ethanoate, CH3COOCH2CH3. The ester group –COO– is in blue.
You do not need balanced equations for these reactions: word equations are enough.
How to answer each type of question
Reaction with a carbonate: observations and products
2 to 3 marksGrade 5
Name the salt: metal name + acid stem + '-oate', e.g. potassium propanoate.
The other products are water and carbon dioxide.
Observation: fizzing or bubbles; the gas turns limewater milky.
Example. Propanoic acid is added to calcium carbonate. (a) Give one observation. (b) Complete the word equation. propanoic acid + calcium carbonate → ____________ + water + ____________
Carboxylic acid + alcohol → ester + water, with an acid catalyst.
Ethanol and ethanoic acid make ethyl ethanoate.
Name the catalyst: an acid, e.g. concentrated sulfuric acid.
Example. Ethyl ethanoate is used as a solvent in some nail varnish removers. (a) Name the alcohol and the carboxylic acid used to make ethyl ethanoate. (b) Name the other product of the reaction and the type of catalyst used.
Show the model answerHide the model answer
(a) Ethanol (1) and ethanoic acid (1) (b) Water (1); an acid catalyst, e.g. sulfuric acid (1)
Don’t lose marks
Forgetting to count the carbon in –COOH: CH3COOH is ethanoic acid (2 carbon atoms), not methanoic acid.
Saying carbonates give hydrogen. Carbonates give carbon dioxide; hydrogen comes from reactions with metals.
Naming the salt wrongly, e.g. 'sodium ethanol' or 'sodium ethanoic'. It is sodium ethanoate.
Leaving out the acid catalyst or the water when describing how an ester is made.
More tips
Memory tricks
Acid + carbonate: fizzing means carbon dioxide. Test it with limewater.
Ester names: the alcohol part comes first and ends in '-yl'; the acid part comes second and ends in '-oate'. Ethanol + ethanoic acid → ethyl ethanoate.
'-oic acid' is the carboxylic acid; '-oate' is its salt or ester.
Exam technique
Balanced equations are not needed for carboxylic acid reactions; give clear word equations with correct names.
For carbonate reactions, give an observation (fizzing, solid disappears) as well as the name of the gas.
What each grade needs
What you need to be able to do, from the first marks up to the top grade.
Grade 3
Name the functional group of carboxylic acidsThe –COOH group.
Grade 4
Name the first four carboxylic acidsMethanoic, ethanoic, propanoic and butanoic acid; ethanoic acid is CH3COOH.
Grade 5
Describe the reaction with carbonatesFizzing as carbon dioxide is given off; a salt and water also form, e.g. sodium ethanoate.
Grade 5
Describe how an ester is madeCarboxylic acid + alcohol, with an acid catalyst, gives an ester and water: ethanoic acid + ethanol → ethyl ethanoate + water.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
What is the functional group of the carboxylic acids?
–COOH
A student added ethanoic acid to sodium carbonate. Give one observation.
Fizzing (bubbles).
Name the carboxylic acid HCOOH.
Methanoic acid
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
(a) What is the functional group of the carboxylic acids?[1]
(b) Name the carboxylic acid with the formula CH3COOH.[1]
(c) Name the gas produced when a carboxylic acid reacts with a carbonate.[1]
(d) Name the ester produced when ethanol reacts with ethanoic acid.[1]
Show the answer and mark scheme
(a)Answer: –COOH
–COOH
(b)Answer: Ethanoic acid
ethanoic acid
(c)Answer: Carbon dioxide
carbon dioxide
(d)Answer: Ethyl ethanoate
ethyl ethanoate
Question 2Medium6 marks
Ethanoic acid is a carboxylic acid.
(a) A student added ethanoic acid to sodium carbonate. Give one observation.[1]
(b) Name the salt formed in this reaction.[1]
(c) Describe a test for the gas produced and give the result.[2]
(d) Ethanoic acid reacts with ethanol to produce an ester. Name the catalyst used and the other product of the reaction.[2]
Show the answer and mark scheme
(a)Answer: Fizzing (bubbles).
fizzing / bubbles / the solid disappears
(b)Answer: Sodium ethanoate
sodium ethanoate
(c)Answer: Bubble the gas through limewater: it turns milky.
bubble the gas through limewater
the limewater turns milky / cloudy
(d)Answer: An acid catalyst (concentrated sulfuric acid); water.