IGCSE Chemistry 2020 0620/62 Feb/Mar

IGCSE 2020 0620/62 Feb/Mar (pdf)

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1. The table gives the boiling points of four alcohols.
   The apparatus shown can be used to separate a mixture of the four alcohols shown in the table.
   (a) Name the apparatus labelled A and B.
   (b) Add to the diagram one arrow to show where water enters the condenser.
   (c) (i) Why is it not safe to heat the mixture of alcohols with a Bunsen burner?
   (ii) Suggest how the mixture of alcohols can be heated safely?
   (d) Describe how the condenser allows the alcohol to be collected as a liquid.
   (e) Which alcohol would be collected first?
   Explain your answer.
   
2. A student investigated the time taken to collect 40cm³ of hydrogen gas when magnesium reacts with dilute sulfuric acid.
   Five experiments were done using the apparatus shown
   Experiment 1
   ● Using a measuring cylinder, 8cm³ of dilute sulfuric acid was poured into the boiling tube. ● Using a second measuring cylinder, 12cm³ of distilled water was added to the acid in the boiling tube. ● The apparatus was set up as shown in the diagram, ensuring the inverted measuring cylinder was full of water. ● The bung was removed from the boiling tube. ● A coiled length of magnesium ribbon was added to the boiling tube, the bung was immediately replaced and a timer started. ● The time taken for 40cm³ of gas to be collected was measured. ● The student felt the outside of the boiling tube. (a) (i) The student noticed that the boiling tube was warm.
   What does this tell you about the type of reaction?
   (ii) Describe one change that could be made to the apparatus to help keep the temperature of the contents of the boiling tube constant during the reaction.
   Experiment 2
   ● The boiling tube was rinsed out with distilled water. ● Experiment 1 was repeated using 10cm³ of dilute sulfuric acid and 10cm³ of distilled water.
   Experiment 3
   ● Experiment 2 was repeated using 12cm³ of dilute sulfuric acid and 8cm³ of distilled water.
   Experiment 4
   ● Experiment 2 was repeated using 16cm³ of dilute sulfuric acid and 4cm³ of distilled water.
   Experiment 5
   ● Experiment 2 was repeated using 20cm³ of dilute sulfuric acid and no distilled water.
   (b) Use the information in the description of the experiments and the timer diagrams to complete the table. Record the time in seconds.
   (c) Add a suitable scale to the y-axis and plot the results from Experiments 1 to 5 on the grid. Draw a smooth line graph.
   (d) (i) From your graph, deduce the time taken to collect 40cm³ of gas if the experiment was repeated using 9cm³ of dilute sulfuric acid.
   Show clearly on the grid how you worked out your answer.
   (ii) What volume of distilled water would be needed if the experiment was repeated using 9cm3 of dilute sulfuric acid?
   (e) The rate of reaction can be calculated using the equation shown.
   rate of reaction = volume of gas collected
   time taken to collect the gas
   (i) Use this equation to calculate the rate of reaction in Experiment 1. Give the units for the rate of reaction you have calculated.
   rate of reaction = …. units = ….
   (ii) In which Experiment, 1, 2, 3, 4 or 5, was the rate of reaction greatest?
   (f) Why would measuring the volume of dilute sulfuric acid with a burette rather than a measuring cylinder be an improvement?
   (g) The magnesium starts to react with the dilute sulfuric acid as soon as it is added.
   (i) Why does this decrease the accuracy of the investigation?
   (ii) Describe one improvement that you could make to overcome this problem.

3. Solution J and solid K were analysed.
   (a) Use the observation from test 1 to suggest the pH of solution J.
   (b) Name the gas given off in test 2.
   (c) Identify solution J
   tests on solid K
   Solid K was ammonium nitrate.
   Complete the expected observations.
   Solid K was dissolved in water to produce solution K. Solution K was divided into two equal portions.
   (d) About 1cm³ of dilute nitric acid and a few drops of aqueous barium nitrate were added to the first portion of solution K. observations
   (e) 2cm³ of aqueous sodium hydroxide was added to the second portion of solution K. The mixture was warmed and the gas given off was tested.
   
4. A black dye can be obtained from some plant roots.
   Plan an investigation to determine how many different coloured substances are contained in a black dye obtained from plant roots.
   You must include how the results you obtain will tell you how many different coloured substances are contained in the black dye.
   You have access to plant roots and all normal laboratory apparatus.

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