Chemistry 0620/61 October/November 2020: question paper and mark scheme

Question

The table gives the boiling points of four alcohols. alcohol boiling point / °C butanol 117 ethanol 79 pentanol 138 propanol 97 The apparatus shown can be used to obtain propanol from a mixture containing butanol, ethanol, pentanol and propanol. A B mixture of alcohols alcohol collected water electric heater (a) Name the items of apparatus labelled A and B. A …… B …… [2] (b) Name this method of separation. . …… [2] (c) Explain why it is safer to heat the mixture of alcohols in the way shown rather than with a Bunsen burner. . …… [1] (d) Describe how propanol can be obtained from the mixture. Use data from the table. . …… . …… . …… [2] (e) Explain why the apparatus in the diagram cannot be used to obtain butanol from the mixture. . …… . …… [1] [Total: 8]

Question

A student investigated the mass of lead(II) iodide precipitate formed when aqueous potassium iodide reacts with aqueous lead(II) nitrate. The equation for the reaction is shown. 2KI(aq) + Pb(NO3)2(aq) → PbI2(s) + 2KNO3(aq) The student did seven experiments. Experiment 1 ●● Using a 50 cm3 measuring cylinder, 25 cm3 of aqueous potassium iodide was poured into a beaker. ●● Using a clean 50 cm3 measuring cylinder, 10 cm3 of aqueous lead(II) nitrate was added to the aqueous potassium iodide in the beaker. The solutions were mixed together. ●● The mass of the precipitate of lead(II) iodide formed was found. Experiment 2 Experiment 1 was repeated using a larger volume of aqueous lead(II) nitrate than in ●● Experiment 1. Experiment 3 Experiment 1 was repeated using a larger volume of aqueous lead(II) nitrate than in ●● Experiment 2. Experiment 4 Experiment 1 was repeated using a larger volume of aqueous lead(II) nitrate than in ●● Experiment 3. Experiment 5 Experiment 1 was repeated using a larger volume of aqueous lead(II) nitrate than in ●● Experiment 4. Experiment 6 Experiment 1 was repeated using a larger volume of aqueous lead(II) nitrate than in ●● Experiment 5. Experiment 7 Experiment 1 was repeated using a larger volume of aqueous lead(II) nitrate than in ●● Experiment 6. (a) Use the measuring cylinder diagrams to complete the table. volume of aqueous measuring cylinder volume of mass of lead(II) experiment potassium iodide diagram for aqueous aqueous lead(II) iodide precipitate / cm3 lead(II) nitrate nitrate / cm3 /g 1 25 10 1.4 20 2 25 2.3 10 30 3 25 3.3 20 30 4 25 4.1 20 40 5 25 5.1 30 50 6 25 5.1 40 50 7 25 5.1 40 [2] (b) Plot the results from Experiments 1 to 7 on the grid. Draw two straight lines through the points. Extend your straight lines so that they meet. 6.0 5.0 4.0 mass of lead(II) iodide precipitate / g 3.0 2.0 1.0 0.0 0 10 20 30 40 50 volume of aqueous lead(II) nitrate / cm3 [5] From your graph, deduce the mass of lead(II) iodide precipitate that would be formed if (c) Experiment 1 was repeated using 20 cm3 of aqueous lead(II) nitrate. Show clearly on the grid how you worked out your answer. mass = …… g [2] (d) Explain why the same mass of precipitate is formed in Experiment 5, Experiment 6 and Experiment 7. . …… . …… [1] (e) Sketch on the grid the graph you would expect if all of the experiments were repeated using aqueous potassium iodide with half the concentration. [2] (f) (i) State why using a 25.0 cm3 pipette to measure the volume of aqueous potassium iodide would be an improvement. . …… . …… [1] State why a 25.0 cm3 pipette could not be used to measure the volume of (ii) aqueous lead(II) nitrate in each experiment. . …… . …… [1] (g) Describe how the solid lead(II) iodide can be separated from the reaction mixture and its mass found. . …… . …… . …… . …… . …… . …… [3] [Total: 17]

Question

Solid Y and solid Z were analysed. Tests were done on each solid. tests on solid Y observations Solid Y was dissolved in distilled water to form solution Y. Solution Y was divided into four portions in four boiling tubes. test 1 Aqueous ammonia was added dropwise and a white precipitate formed which then in excess to the first portion of solution Y. was insoluble in excess test 2 Aqueous sodium hydroxide was added a white precipitate formed which dissolved dropwise and then in excess to the second in excess to form a colourless solution portion of solution Y. test 3 A piece of aluminium foil was added to the the gas turned damp red litmus paper blue solution formed in test 2. The mixture was warmed and any gas given off was tested. test 4 About 1 cm3 of dilute nitric acid and a few drops the solution remained colourless, of aqueous silver nitrate were added to the third no precipitate formed portion of solution Y. (a) Name the gas given off in test 3. . …… [1] (b) Identify solid Y. . …… . …… [2] (c) A strip of universal indicator paper was dipped into the fourth portion of solution Y. The universal indicator paper turned orange. What additional information does this give about solution Y? . …… [1] tests on solid Z Solid Z was iron(II) sulfate. Complete the expected observations. Solid Z was dissolved in water to produce solution Z. Solution Z was split into three equal portions in three boiling tubes. (d) Aqueous ammonia was added dropwise and then in excess to the first portion of solution Z. observations …… . …… . …… [2] (e) About 2 cm3 of dilute hydrochloric acid was added to the second portion of solution Z. observations …… [1] (f) The solution from (e) was warmed and a piece of filter paper soaked in acidified aqueous potassium manganate(VII) was held at the mouth of the boiling tube. observations …… [1] (g) About 1 cm3 of dilute nitric acid followed by a few drops of aqueous barium nitrate were added to the third portion of solution Z. observations …… [1] [Total: 9]

Question

A mixture contains three solid compounds: ●● copper(II) sulfate ●● cetyl alcohol ●● silicon dioxide. The table gives some information on the solubility of these three solids. solubility in solubility in name of compound water propanone copper(II) sulfate soluble insoluble cetyl alcohol insoluble soluble silicon dioxide insoluble insoluble Plan a method to obtain a pure sample of each of the three solids, copper(II) sulfate, cetyl alcohol and silicon dioxide, from the mixture. You have access to normal laboratory apparatus. . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… . …… [6]