1. 1
   A food scientist studies vinegar, which is an aqueous solution of ethanoic acid used to flavour and preserve pickled vegetables. She investigates how ethanoic acid reacts with sodium carbonate, added to test its acidity, and later compares it with a stronger mineral acid.

   (a)

   A food scientist studies vinegar, an aqueous solution of ethanoic acid used to flavour and preserve pickled vegetables. Carboxylic acids such as ethanoic acid all contain which functional group?

   [1 mark]

   • A-COOH
   • B-OH
   • CC=C
   • D-NH2

   (b)

   The scientist adds a spoonful of sodium carbonate powder to a sample of vinegar. Bubbles of gas are produced immediately. Which gas is produced, and how could it be confirmed?

   [1 mark]

   • AHydrogen, confirmed because a lit splint gives a squeaky pop
   • BCarbon dioxide, confirmed because it turns limewater milky/cloudy
   • COxygen, confirmed because a glowing splint relights
   • DChlorine, confirmed because it bleaches damp litmus paper

   (c)

   The scientist then measures the pH of vinegar (ethanoic acid) and compares it with a solution of hydrochloric acid of the same concentration. She finds that the vinegar has a higher pH than the hydrochloric acid. Explain this observation in terms of ionisation.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A perfumer is developing a new fragrance and wants to produce a pleasant-smelling compound by reacting ethanoic acid with ethanol in the presence of a small amount of acid catalyst, gently warming the mixture.

   (a)

   A perfumer wants to produce a pleasant-smelling ester for a new fragrance. She reacts ethanoic acid with ethanol in the presence of an acid catalyst. Which type of compound is formed, along with water?

   [1 mark]

   • AAn alkane
   • BAn alkene
   • CAn alcohol
   • DAn ester

   (b)

   The perfumer notices that the ester she has made is far less soluble in water and has a much weaker odour of vinegar than the ethanoic acid she started with. This is because, compared with ethanoic acid, the ester molecule:

   [1 mark]

   • AHas gained an additional -COOH group during the reaction
   • BStill contains an unreacted -COOH group in exactly the same form
   • CNo longer contains the -COOH functional group, since it has reacted to form a different functional group
   • DIs identical in structure to ethanoic acid but with a different name

   (c)

   Name the ester produced when ethanoic acid reacts with ethanol, and write a word equation for the reaction.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A cleaning products company is developing a descaling solution using methanoic acid, one of the first four members of the carboxylic acid homologous series: methanoic, ethanoic, propanoic and butanoic acid.

   (a)

   Describe what happens when a carboxylic acid such as methanoic acid dissolves in water, and describe how carboxylic acids react with metal carbonates.

   [3 marks]

   (b)

   The company's chemists want to explain, using the concept of ionisation, why methanoic acid is described as a weak acid rather than a strong acid like hydrochloric acid, and why this affects how vigorously it reacts with limescale (calcium carbonate) compared with an equally concentrated strong acid.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An archaeologist studying ancient food preservation techniques finds evidence that early civilisations fermented fruit juices beyond the alcohol stage, producing a sour liquid used to preserve food, in a process similar to how vinegar is made today.

   (a)

   Explain how ethanoic acid could be produced from ethanol, and describe the properties of ethanoic acid that make it useful, both historically and today, as a food preservative.

   [6 marks]

   (b)

   The archaeologist also finds evidence that some ancient perfume-makers combined this sour liquid with fermented alcohol to create pleasant-smelling substances. Explain the reaction that would occur between a carboxylic acid and an alcohol, including the type of product formed, and explain why this reaction supports the idea that early perfume-makers were producing esters, even without understanding the chemistry involved.

   [6 marks]

   Total for question 4: 12 marks

End of questions