1. 1
   A student carries out a titration to find the volume of hydrochloric acid needed to exactly neutralise a fixed volume of sodium hydroxide solution, using a few drops of phenolphthalein indicator, which is pink in alkaline solution and colourless in acidic or neutral solution.

   (a)

   Which piece of apparatus is used to add the acid slowly and measure its volume accurately?

   [1 mark]

   • AA burette
   • BA measuring cylinder
   • CA beaker
   • DA test tube

   (b)

   What colour change would the student observe in the flask at the exact end point of this titration?

   [1 mark]

   • APink to colourless
   • BColourless to pink
   • CBlue to red
   • DRed to blue

   (c)

   Describe how the student should add the acid from the burette as the end point is approached, to find the volume needed accurately.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A different student titrates sulfuric acid against potassium hydroxide solution in order to standardise a new batch of acid before it is used in further experiments.

   (a)

   Which of the following acids may be used in the titrations covered by this specification, alongside sulfuric acid?

   [1 mark]

   • AHydrochloric acid and nitric acid, since these are also strong acids
   • BEthanoic acid, since it is commonly available
   • CCarbonic acid, since it is found in fizzy drinks
   • DAny acid, regardless of its strength

   (b)

   Why is it important that only strong acids and strong alkalis are used in these titrations, rather than weak ones?

   [1 mark]

   • AStrong acids and alkalis ionise fully in solution, giving a sharp, easily detected colour change at the end point
   • BStrong acids and alkalis are cheaper to buy than weak ones
   • CWeak acids and alkalis are too dangerous to use in a school laboratory
   • DStrong acids and alkalis do not react with indicators

   (c)

   Describe how the student uses a rough titration followed by accurate repeat titrations to obtain a reliable titre value.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student carries out the required practical to establish the concentration of an unknown strong acid by titration with a standard sodium hydroxide solution of known concentration.

   (a)

   Describe how the student should set up this titration, including the apparatus used.

   [3 marks]

   (b)

   Describe how the student ensures the titre results used to calculate the concentration are accurate and reliable.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A quality control laboratory must regularly titrate batches of nitric acid solution against a standard sodium hydroxide solution to check that the concentration of the acid is consistent between different production runs.

   (a)

   A quality control laboratory must titrate a batch of nitric acid solution against a standard sodium hydroxide solution to check that its concentration is consistent between production runs. Describe, in full, a suitable method the laboratory technician should follow to carry out this titration accurately, including the apparatus used, the indicator, and appropriate safety precautions.

   [6 marks]

   (b)

   Evaluate how the laboratory technician can ensure that the titration results obtained are both precise and accurate, and explain why this matters for quality control between different production runs.

   [6 marks]

   Total for question 4: 12 marks

End of questions