Paper 6 style practice paper: Alternative to practical — question paper

Section A: Experimental techniques[15 marks]

Answer all questions in the spaces provided. The marks for each part are shown in brackets.

1. 1

   A student carries out a titration to find the volume of aqueous sodium hydroxide needed to neutralise 25.0 cm³ of dilute hydrochloric acid. The burette readings are shown in the table.

   Burette readings

   Titration	Final reading / cm³	Initial reading / cm³
   1	24.60	2.10
   2	25.15	2.65
   3	46.10	21.55

   1. (a)

      State the colour change seen at the end-point when methyl orange is used and alkali is added to the acid.

      [1]
   2. (b)

      Explain why each reading must be taken with the eye level with the bottom of the meniscus.

      [1]
   3. (c)

      Use the table to calculate the average volume of alkali used. Choose the concordant results.

      [2]
2. 2

   Dilute hydrochloric acid is added to an unknown white solid. A gas is produced that turns limewater milky.

   1. (a)

      Name the gas produced.

      [1]
   2. (b)

      Name the ion in the solid that produced this gas.

      [1]
   3. (c)

      Describe the test and the result used to show that a gas is hydrogen.

      [1]
   4. (d)

      State the test used to show that a solution contains sulfate ions.

      [1]
3. 3

   A student separates the dyes in a food colouring by paper chromatography, using water as the solvent. The solvent front travels 8.0 cm from the start line and one dye travels 6.0 cm.

   1. (a)

      Calculate the Rf value of this dye.

      [2]
   2. (b)

      State what the student can conclude if the colouring produces two separate spots.

      [1]
   3. (c)

      State why the start line is drawn in pencil rather than in ink.

      [1]
4. 4

   A mixture contains sand, salt and water.

   1. (a)

      Name the technique used to separate the sand from the salt solution.

      [1]
   2. (b)

      Name the technique used to obtain solid salt from the solution.

      [1]
   3. (c)

      State how the student could show that the salt obtained is pure.

      [1]

Section B: Observations, analysis and planning[15 marks]

Answer all questions in the spaces provided. The marks for each part are shown in brackets.

1. 5

   A student plans an experiment to find out how the concentration of dilute hydrochloric acid affects the rate of reaction with 2.0 g of marble chips.

   1. (a)

      State the apparatus the student should use to measure the volume of gas produced.

      [1]
   2. (b)

      State two variables the student must keep constant in this experiment.

      [2]
   3. (c)

      Describe how the student can tell from the results that the more concentrated acid reacts faster.

      [2]
2. 6

   A student heats a few blue crystals of hydrated copper(II) sulfate in a test tube.

   1. (a)

      State two observations the student would make.

      [2]
   2. (b)

      Explain what these observations show about the crystals.

      [2]
   3. (c)

      State one safety precaution the student should take when heating the crystals.

      [1]
3. 7

   A student tests an unknown solution Z. Adding dilute nitric acid and then aqueous silver nitrate gives a white precipitate. Adding aqueous sodium hydroxide gives a blue precipitate.

   1. (a)

      Name the anion present in Z.

      [1]
   2. (b)

      Name the cation present in Z.

      [1]
   3. (c)

      State the observation the student would make if aqueous ammonia were added to the blue precipitate until it is in excess.

      [1]
   4. (d)

      Describe the test and the result that would show that Z does not contain sulfate ions.

      [2]