Required practicals practice paper: Methods, variables, graphs and evaluation — question paper

Section A: Multiple-choice questions[10 marks]

Choose one answer for each question. Each question is worth 1 mark.

1. 1

   The apparatus for adding acid drop by drop in a titration is the

   1. Ameasuring cylinder
   2. Bburette
   3. Cpipette filler
   4. Devaporating basin
   ( )
2. 2

   A temperature-change practical measures the temperature of the

   1. Aflame
   2. Bbunsen
   3. Csurroundings (the solution mixture)
   4. Dthermometer case
   ( )
3. 3

   In the rate experiment with a gas syringe, the independent variable for a concentration study is the

   1. Aacid concentration
   2. Bgas volume
   3. Ctime
   4. Dtemperature of the lab
   ( )
4. 4

   The chromatography baseline is drawn in pencil because pencil is

   1. Adarker
   2. Binsoluble and will not move
   3. Ccheaper
   4. Deasier to erase
   ( )
5. 5

   To find the mass of dissolved solids in a water sample you should

   1. Afilter the sample
   2. Btaste the sample
   3. Cevaporate a measured volume to dryness and weigh the residue
   4. Dmeasure its pH
   ( )
6. 6

   The electrolysis half equation at the anode for molten lead bromide is

   1. APb²⁺ + 2e⁻ → Pb
   2. BBr₂ + 2e⁻ → 2Br⁻
   3. CPb → Pb²⁺ + 2e⁻
   4. D2Br⁻ → Br₂ + 2e⁻
   ( )
7. 7

   In the salt-making practical, the copper oxide is added in excess to ensure

   1. Athe solution turns blue
   2. Ball the acid reacts
   3. Cthe mixture boils
   4. Dthe crystals dissolve
   ( )
8. 8

   A fair test for the effect of concentration on rate must control the

   1. Aconcentration
   2. Btime readings
   3. Ctemperature and surface area
   4. Dgas syringe size
   ( )
9. 9

   Titration results are repeated until readings are

   1. Aconcordant (within about 0.1 cm³)
   2. Bidentical
   3. Call above 25 cm³
   4. Drounded up
   ( )
10. 10

    Which observation shows a reaction is endothermic?

    1. AThe mixture warms up
    2. BGas bubbles form
    3. CA precipitate forms
    4. DThe thermometer reading falls
    ( )

Section B: Structured questions[50 marks]

Answer all questions in the spaces provided.

1. 11

   This question is about the temperature-change practical. A student mixes 25 cm³ of sodium hydroxide solution with 25 cm³ of hydrochloric acid and records the maximum temperature rise. The experiment is repeated with different volumes of acid (total volume always 50 cm³).

   1. (a)

      State the independent and dependent variables.

      [2]
   2. (b)

      State three quantities that must be controlled.

      [3]
   3. (c)

      Describe how the results identify the exact volumes for complete neutralisation.

      [3]
   4. (d)

      State two sources of error and one improvement.

      [2]
2. 12

   This question is about the rates practical. A student drops magnesium ribbon into hydrochloric acid and collects hydrogen in a gas syringe, recording the volume every 10 seconds for four acid concentrations.

   1. (a)

      State the independent variable, the dependent variable and two control variables.

      [4]
   2. (b)

      Describe how the results show which concentration reacts fastest.

      [2]
   3. (c)

      State one limitation of the gas syringe and one limitation of timing by eye.

      [2]
   4. (d)

      State why the experiment is repeated and how the data should be processed.

      [2]
3. 13

   This question is about the chromatography practical. A student analyses a food colouring suspected of containing banned dyes.

   1. (a)

      Describe the method, including two precautions.

      [4]
   2. (b)

      The colouring separates into three spots. What does this show?

      [1]
   3. (c)

      Spot A moves 5.2 cm and the solvent front moves 6.5 cm. Calculate the Rf value of A.

      [2]
   4. (d)

      Explain how reference dyes help identify the components.

      [2]
   5. (e)

      State one reason a dye with a higher Rf travels further.

      [1]
4. 14

   This question is about the water-analysis practical. A student analyses a sample of reservoir water.

   1. (a)

      Describe how to measure the pH of the sample.

      [2]
   2. (b)

      The student evaporates 100 cm³ of the sample and the residue has a mass of 0.38 g. Calculate the dissolved solids in g/dm³.

      [2]
   3. (c)

      Describe how the student distils the sample and tests the distillate for purity.

      [4]
   4. (d)

      Explain why the dissolved solids remain in the flask during distillation.

      [2]
5. 15

   This question is about making a pure dry salt and titration. A student makes zinc sulfate crystals from zinc carbonate and dilute sulfuric acid, then titrates leftover solutions.

   1. (a)

      Describe the method for making pure, dry zinc sulfate crystals.

      [5]
   2. (b)

      Explain why zinc carbonate rather than zinc oxide could be confirmed as fully reacted.

      [2]
   3. (c)

      In a titration to standardise the leftover acid, the titre values are 24.35 cm³, 24.30 cm³ and 26.10 cm³. Calculate the mean titre, explaining your choice of values.

      [3]