1. 1
   A student tests four unknown solutions (P, Q, R and S) with universal indicator and records the colours produced. Solution P turns the indicator red, solution Q turns it green, solution R turns it purple, and solution S turns it orange.

   (a)

   Which ion is responsible for solution P being acidic?

   [1 mark]

   • AH+(aq) ions
   • BOH-(aq) ions
   • CNa+(aq) ions
   • DCl-(aq) ions

   (b)

   Solution R turns universal indicator purple. Which pH value best matches this result?

   [1 mark]

   • ApH 1
   • BpH 7
   • CpH 13
   • DpH 4

   (c)

   Describe how the student could use universal indicator to estimate the approximate pH of each solution.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A technician slowly adds sodium hydroxide solution to hydrochloric acid while monitoring the pH with a data logger throughout the addition.

   (a)

   Which ion in the sodium hydroxide solution causes the pH to rise as it is added?

   [1 mark]

   • ANa+(aq) ions
   • BOH-(aq) ions
   • CH+(aq) ions
   • DCl-(aq) ions

   (b)

   At the point where exactly enough sodium hydroxide has been added to react completely with all the acid, what is the approximate pH of the mixture?

   [1 mark]

   • ApH 3
   • BpH 1
   • CpH 14
   • DpH 7

   (c)

   Write the ionic equation for the neutralisation reaction taking place, and state what happens to the ions involved.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A farmer has a field with acidic soil that is limiting crop growth. To correct this, the farmer spreads powdered calcium hydroxide (agricultural lime) over the field and wants to check whether the treatment has worked.

   (a)

   Explain, in terms of ions, why adding calcium hydroxide to the acidic field soil raises its pH.

   [3 marks]

   (b)

   Describe a method the farmer could use to compare the pH of the soil before and after treatment with calcium hydroxide, using universal indicator, and explain how to make the comparison a fair test.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An indigestion tablet containing magnesium hydroxide is used to treat excess stomach acid. A science technician demonstrates its effect by adding a crushed tablet to a beaker of dilute hydrochloric acid and monitoring the pH with universal indicator before and after.

   (a)

   Explain fully, in terms of ions, how magnesium hydroxide in the indigestion tablet neutralises excess acid in the stomach, including the ionic equation for the reaction.

   [6 marks]

   (b)

   Evaluate why measuring pH with universal indicator only gives an approximate value, compared with using a calibrated pH meter, and discuss the effect this has on the reliability of the technician's demonstration.

   [6 marks]

   Total for question 4: 12 marks

End of questions