IGCSE Chemistry 2020 0620/63 May/June

IGCSE 2020 0620/63 May/June (pdf)

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1. A sample of rock salt contains sodium chloride and sand.
   Sodium chloride is soluble in water. Sand is insoluble in water.
   A student obtained dry crystals of pure sodium chloride from a lump of rock salt.
   These are some of the steps the student used.
   (a) Name the apparatus labelled A in step 1.
   (b) Explain why the mixture is heated and stirred in step 2.
   (c) (i) Name the apparatus labelled B in step 3.
   (ii) State the scientific term for the sand left on the filter paper in step 3.
   (d) Describe what the student must do after step 3 to obtain dry crystals of pure sodium chloride.
   
2. A student investigated the temperature change when aqueous sodium hydroxide neutralises dilute hydrochloric acid. The equation for the reaction is shown.
   NaOH + HCl → NaCl + H₂O
   Eight experiments were done.
   Experiment 1

• A polystyrene cup was placed into a 250cm³ beaker for support.
• Using a measuring cylinder, 5cm³ of aqueous sodium hydroxide was poured into the polystyrene cup.
• Using a measuring cylinder, 45cm³ of dilute hydrochloric acid was poured into the polystyrene cup.
• The mixture was stirred and the maximum temperature reached was measured using a thermometer.
• The polystyrene cup was rinsed with distilled water.
  Experiment 2
• Experiment 1 was repeated using 10cm³ of aqueous sodium hydroxide and 40cm³ of dilute hydrochloric acid.
  Experiment 3
• Experiment 1 was repeated using 15cm³ of aqueous sodium hydroxide and 35cm³ of dilute hydrochloric acid.
  Experiment 4
• Experiment 1 was repeated using 20cm³ of aqueous sodium hydroxide and 30cm³ of dilute hydrochloric acid.
  Experiment 5
• Experiment 1 was repeated using 30cm³ of aqueous sodium hydroxide and 20cm³ of dilute hydrochloric acid.
  Experiment 6
• Experiment 1 was repeated using 35cm³ of aqueous sodium hydroxide and 15cm³ of dilute hydrochloric acid.
  Experiment 7
• Experiment 1 was repeated using 40cm³ of aqueous sodium hydroxide and 10cm³ of dilute hydrochloric acid.
  Experiment 8
• Experiment 1 was repeated using 45cm³ of aqueous sodium hydroxide and 5cm³ of dilute hydrochloric acid.
  (a) Use the information in the description of the experiments and the thermometer diagrams to complete the table.
  (b) Plot the results from Experiments 1 to 8 on the grid. Draw two straight lines through the points.
  Extend your straight lines so that they cross.
  (c) The point on the graph where the two straight lines cross is where all of the aqueous sodium hydroxide reacts with all of the dilute hydrochloric acid to form a neutral solution.
  (i) Use your graph to deduce the volume of aqueous sodium hydroxide and the volume of dilute hydrochloric acid that react together to produce a neutral solution.
  Show your working on the grid.
  (ii) Use your graph to determine the highest temperature reached if the volumes in (c)(i) were mixed together.
  (iii) Which solution, aqueous sodium hydroxide or dilute hydrochloric acid, was the most concentrated?
  Use your answer to (c)(i) to explain why.
  (d) On the graph, sketch the lines you would expect to obtain if a copper can was used instead of a polystyrene cup.
  (e) Give one advantage and one disadvantage of using a burette, instead of a measuring cylinder, to add the dilute hydrochloric acid directly into the polystyrene cup.
  (f) How could the reliability of the results of this investigation be checked?

3. Two solids, solid N and solid P, were analysed.
   Tests were done on each solid.
   tests on solid N
   Tests were done and the following observations made.
   (a) Name the gas given off in test 3.
   (b) Identify solid N.
   tests on solid P
   Solid P was potassium iodide.
   Complete the expected observations.
   (c) Describe the appearance of solid P.
   (d) A flame test was done on solid P.
   (e) Solid P was dissolved in distilled water to produce solution P. Solution P was divided into three equal portions in three test-tubes.
   (i) About 1cm depth of dilute nitric acid and a few drops of aqueous silver nitrate were added to the first portion of solution P.
   (ii) About 1cm depth of dilute nitric acid and a few drops of aqueous barium nitrate were added to the second portion of solution P.
   (iii) A few drops of aqueous bromine were added to the third portion of solution P.
   
4. Stayclean and Brightwhite are two brands of washing powder. Both contain sodium carbonate. Sodium carbonate is soluble in water and reacts with dilute sulfuric acid to produce carbon dioxide gas.
   Plan an investigation to determine which of the two washing powders, Stayclean or Brightwhite, contains the greatest percentage of sodium carbonate.
   You are provided with samples of the two washing powders and common laboratory apparatus and chemicals.

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