1. 1
   A food-safety technician is testing several kitchen liquids to check whether they are acidic or alkaline, starting with a sample of lemon juice and then a dilute solution of soap flakes in water, using different indicators for each test.

   (a)

   A food-safety technician tests a sample of lemon juice by adding a few drops of litmus solution. The lemon juice is known to be acidic. What colour does the litmus turn?

   [1 mark]

   • ABlue
   • BRed
   • CColourless
   • DGreen

   (b)

   The same technician then adds a few drops of phenolphthalein indicator to the soap solution, which is alkaline. What colour does the phenolphthalein turn?

   [1 mark]

   • AColourless
   • BYellow
   • CPink
   • DOrange

   (c)

   Describe how methyl orange indicator could be used to distinguish between the acidic lemon juice and the alkaline soap solution, stating the colour observed in each case.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   An environmental officer is investigating whether emissions from a nearby factory are affecting the acidity of local rainwater, and tests several rainwater samples collected over a week using universal indicator solution and a colour chart.

   (a)

   An environmental officer collects a rainwater sample near a factory and measures its pH using universal indicator, finding a pH of 5. How should this rainwater be classified?

   [1 mark]

   • AWeakly acidic
   • BStrongly acidic
   • CNeutral
   • DWeakly alkaline

   (b)

   On a different day, the officer tests a sample of rainwater and finds it has a pH of 13. How should this sample be classified?

   [1 mark]

   • AWeakly acidic
   • BNeutral
   • CWeakly alkaline
   • DStrongly alkaline

   (c)

   Describe how the environmental officer would use universal indicator to measure the approximate pH of a rainwater sample.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A pharmacist is advising a patient about how indigestion tablets work: the tablets contain a mild alkali designed to neutralise excess hydrochloric acid produced in the stomach, and the pharmacist wants to explain the chemistry involved as well as how the exact neutralising strength of a batch of tablets could be checked in a laboratory.

   (a)

   A pharmacist explains to a patient that indigestion tablets contain a mild alkali that neutralises excess acid in the stomach. In terms of ions, explain what is meant by an acid and what is meant by an alkali, and describe what happens when they react together.

   [3 marks]

   (b)

   The pharmaceutical company wants to check the neutralising strength of a batch of indigestion tablets by reacting a dissolved tablet solution with a standard acid of known concentration. Describe how an acid-alkali titration could be carried out to find the volume of acid needed to exactly neutralise a fixed volume of the dissolved tablet (alkali) solution.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A quality-control chemist at a vinegar bottling plant is testing a batch of vinegar to check its ethanoic acid concentration meets the company's labelling standard, using a titration against a standard sodium hydroxide solution, and must ensure the results are as accurate and reliable as possible before the batch is approved for sale.

   (a)

   A quality-control chemist at a vinegar bottling plant needs to determine the concentration of ethanoic acid in a batch of vinegar by titrating it against a standard sodium hydroxide solution of known concentration. Describe, in full detail, the practical procedure the chemist should follow to carry out this titration accurately, from setting up the apparatus to identifying the end point.

   [6 marks]

   (b)

   The quality-control chemist obtains slightly different titre volumes across three repeat titrations of the same vinegar sample. Explain why repeat titrations are necessary, identify possible sources of error in the titration procedure, and suggest how the chemist could improve the accuracy and reliability of the final result.

   [6 marks]

   Total for question 4: 12 marks

End of questions