1. 1
   A technician is given an unlabelled white solid and carries out two tests. First, she adds a little of the solid to dilute nitric acid and holds a lit splint at the mouth of the test tube: the gas produced extinguishes the flame with a slight crackling sound. She then acidifies a fresh sample of the resulting solution with dilute nitric acid and adds a few drops of aqueous silver nitrate, forming a white precipitate.

   (a)

   The gas produced when the solid reacts with dilute nitric acid extinguishes a lit splint. Which gas has been produced, and what does this identify about the original solid?

   [1 mark]

   • AHydrogen, showing the solid is a metal
   • BOxygen, showing the solid contains a nitrate ion
   • CChlorine, showing the solid contains a chloride ion
   • DCarbon dioxide, showing the solid contains a carbonate ion

   (b)

   The white precipitate formed when acidified silver nitrate is added to the solution could indicate the presence of which ion?

   [1 mark]

   • ASulfate
   • BNitrate
   • CChloride
   • DCarbonate

   (c)

   The technician confirms that the carbon dioxide gas is present by bubbling it through a second solution and observing a colour change. Name this second solution and describe the observation that confirms carbon dioxide is present.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A food safety officer suspects that a sample of orange squash contains an artificial colourless sweetener that is banned in food and drink products. She spots a sample of the squash, alongside a spot of a known pure sample of the banned sweetener, onto the baseline of a sheet of chromatography paper, then stands the paper upright in a shallow layer of a suitable solvent, below the baseline.

   (a)

   Because the sweetener suspected in the squash is colourless, which extra step must the officer take after running the chromatogram in order to see where the spots of sweetener have travelled to?

   [1 mark]

   • AHeat the paper strongly until the colourless spots turn black
   • BSpray or treat the paper with a locating agent that reacts with the sweetener to form a visible spot
   • CNothing extra is needed, since all substances become visible once the solvent evaporates
   • DDip the whole paper in the same solvent a second time

   (b)

   After the locating agent is applied, the spot from the squash sample and the spot from the known pure sweetener sample appear at exactly the same height above the baseline. What does this suggest?

   [1 mark]

   • AThe squash definitely contains no sweetener at all
   • BThe squash sample and the pure sweetener sample must be completely different substances
   • CThe squash sample may well contain the banned sweetener, since matching spots travel the same distance in the same solvent
   • DThe chromatography paper was faulty and the test must be repeated with new paper

   (c)

   The officer measures that the sweetener spot travelled 6.0 cm from the baseline, while the solvent front travelled 8.0 cm from the baseline in the same run. Calculate the Rf value of the sweetener, showing your working.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student is given a mixture of rock salt: solid sodium chloride mixed with insoluble sand. She is asked to produce a sample of pure, dry sodium chloride crystals from this mixture, using only water and standard laboratory apparatus.

   (a)

   Describe how the student could obtain a solution of sodium chloride free of the insoluble sand, and name this separation technique.

   [3 marks]

   (b)

   Describe how the student should then obtain dry, pure crystals of sodium chloride from the filtrate, explaining why the solution should not simply be heated to dryness in one continuous step.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A student plans an experiment to find the exact concentration of a solution of hydrochloric acid using a solution of sodium hydroxide of known concentration. She has access to a burette, a volumetric pipette, a pipette filler, a conical flask, a white tile and a suitable indicator.

   (a)

   Describe how the student should carry out this titration, naming the apparatus used at each stage and explaining why the burette readings should be taken to the nearest 0.05 cm3 and repeated until concordant results are obtained.

   [6 marks]

   (b)

   The student's teacher suggests that, instead of using an indicator, the titration could be monitored using a pH meter or pH sensor to record how the pH changes as acid is added. Suggest one advantage and one disadvantage of using a pH sensor instead of an indicator for this experiment, and explain why this is an example of good experimental design to consider before starting.

   [6 marks]

   Total for question 4: 12 marks

5. 5
   A student is given a blue aqueous solution known to contain a metal salt and adds aqueous sodium hydroxide dropwise. A pale blue precipitate forms at first, and the precipitate remains even when excess sodium hydroxide solution is added.

   (a)

   A pale blue precipitate that does not dissolve in excess aqueous sodium hydroxide indicates the presence of which cation?

   [1 mark]

   • AIron(II)
   • BAluminium
   • CCalcium
   • DCopper(II)

   (b)

   The student repeats the test on a different unknown solution using aqueous ammonia instead of sodium hydroxide. A white precipitate forms and dissolves in excess aqueous ammonia to give a colourless solution. Which cation is present?

   [1 mark]

   • AAluminium
   • BCopper(II)
   • CZinc
   • DIron(III)

   (c)

   Describe how the student could use a flame test to help confirm the presence of a specific metal cation in a third, differently coloured solid sample, and state the flame colour that would confirm the presence of potassium ions.

   [2 marks]

   Total for question 5: 4 marks

6. 6
   A pharmaceutical quality-control chemist titrates a sample of citric acid solution against a standard sodium hydroxide solution of known concentration, using phenolphthalein indicator, to check that a batch of the acid meets its required concentration.

   (a)

   Which piece of apparatus should the chemist use to measure an accurate, fixed volume of the standard sodium hydroxide solution into the conical flask before starting the titration?

   [1 mark]

   • AA measuring cylinder
   • BA volumetric pipette
   • CA beaker
   • DA gas syringe

   (b)

   Phenolphthalein is colourless in acidic solution and pink in alkaline solution. Which observation correctly identifies the end-point of this titration, as citric acid is added from the burette to the alkaline sodium hydroxide solution in the flask?

   [1 mark]

   • AThe point at which the solution turns from pink to colourless and stays colourless with one further drop
   • BThe point at which the solution first turns pink and stays pink permanently
   • CThe point at which the solution begins to boil
   • DThe point at which no further gas bubbles are produced

   (c)

   State the type of reaction taking place between citric acid and sodium hydroxide, and name the general type of compound formed as a product, in addition to water.

   [2 marks]

   Total for question 6: 4 marks

7. 7
   An art conservator is investigating a historic painting and wants to identify the coloured pigments used, without cutting a large sample from the artwork. She removes a tiny fleck of paint, dissolves it in a small amount of a suitable solvent, and runs paper chromatography alongside spots of five known reference pigments.

   (a)

   Explain why paper chromatography, rather than a method requiring a large sample, is a suitable technique for this investigation, and describe how the conservator should set up the experiment to obtain a usable chromatogram.

   [3 marks]

   (b)

   On the finished chromatogram, the spot from the paint sample separates into two separate coloured spots, each matching the height of a different one of the five reference pigment spots. Explain what this result shows about the paint sample, and explain how the conservator could confirm that a chromatography solvent has been left to run for long enough before removing the paper.

   [4 marks]

   Total for question 7: 7 marks

8. 8
   A student is given a mixture of ethanol and water and is asked to separate them, given that ethanol boils at 78°C and water boils at 100°C, and that the two liquids mix completely with each other. The student has access to a round-bottomed flask, a fractionating column, a condenser, a thermometer, a Bunsen burner and a receiving flask.

   (a)

   Name the separation technique the student should use to separate the ethanol from the water, and describe how the apparatus should be set up and used, explaining the purpose of the fractionating column and the thermometer.

   [6 marks]

   (b)

   Suggest one way the student could check the purity of the ethanol collected, and explain why choosing fractional distillation, rather than simple distillation, for this particular mixture is an example of good experimental design.

   [6 marks]

   Total for question 8: 12 marks

End of questions