0620 Chemistry June 2025 Question Paper 63

1 Fermentation is a process in which yeast is used to convert aqueous glucose to ethanol and carbon dioxide. Fermentation takes place at a temperature of between 25 °C and 35 °C. C6H12O6(aq) 2C2H5OH(aq) + 2CO2(g)

A student uses the apparatus shown in Fig. 1.1 to make carbon dioxide by fermentation. B A aqueous glucose and yeast water-bath Fig. 1.1

(a) Name the items of apparatus labelled A and B in Fig. 1.1. A B [2]

(b) Suggest why a water-bath is used [1] , ,

(c) The student measures the volume of gas that is collected every 10 minutes for 90 minutes.

Their results are shown in Fig. 1.2. 0 0 20 40 60 80 100 10 30 20 time / min volume of gas collected / cm3 40 50 60 70 80 90 Fig. 1.2

Describe how the results in Fig. 1.2 show that the fermentation is not complete after 90 minutes [1]

(d) The student repeats the experiment using the apparatus shown in Fig. 1.3. aqueous glucose and yeast water-bath limewater Fig. 1.3

(i) State what happens to the appearance of the limewater during fermentation [1]

(ii) State one observation the student would make that shows that fermentation is complete [1]

(e) State the method the student should use to obtain ethanol from the fermentation mixture [1]

[Total: 7] , ,

2 A student investigates how the rate of reaction between dilute hydrochloric acid and aqueous sodium thiosulfate changes as the concentration of the aqueous sodium thiosulfate decreases. During the reaction, the solution slowly becomes cloudy. As the solution becomes cloudy, it becomes more difficult to see through the solution.

The student does five experiments.

Experiment 1 • Use a 50 cm3 measuring cylinder to pour 50 cm3 of aqueous sodium thiosulfate into a 100 cm3 beaker. • Use a 10 cm3 measuring cylinder to pour 5 cm3 of dilute hydrochloric acid into the beaker containing the aqueous sodium thiosulfate. • Immediately start a stop-watch and stir the contents of the beaker. • Stand the beaker on a printed sheet and look down from above the beaker as shown in Fig. 2.1. eye 100 cm3 beaker printed sheet aqueous sodium thiosulfate and dilute hydrochloric acid mixture printed text Fig. 2.1 • When the text on the printed sheet is not visible, stop the stop-watch and record the time to the nearest whole number of seconds. • Empty the contents of the beaker and rinse the beaker with distilled water.

Experiment 2 • Repeat Experiment 1 using 40 cm3 of aqueous sodium thiosulfate instead of 50 cm3. Use the 50 cm3 measuring cylinder to add 10 cm3 of distilled water to the beaker before adding the dilute hydrochloric acid.

Experiment 3 • Repeat Experiment 2 using 30 cm3 of aqueous sodium thiosulfate and 20 cm3 of distilled water.

Experiment 4 • Repeat Experiment 2 using 25 cm3 of aqueous sodium thiosulfate and 25 cm3 of distilled water.

Experiment 5 • Repeat Experiment 2 using 20 cm3 of aqueous sodium thiosulfate and 30 cm3 of distilled water. , ,

(a) Use the information in the description of the experiments and the stop-watch diagrams to complete Table 2.1. Table 2.1 experiment volume of aqueous sodium thiosulfate / cm3 volume of distilled water / cm3 volume of dilute hydrochloric acid / cm3 stop-watch diagram time taken for text to not be visible / s 1 50 0 5 0 30 15 seconds minutes 45 2 0 30 15 45 3 0 30 15 45 4 0 30 15 45 5 0 30 15 45

[3] , ,

(b) Write a suitable scale on the y-axis and plot the results from Experiments 1 to 5 on Fig. 2.2.

Draw a curve of best fit. 20 25 30 35 volume of aqueous sodium thiosulfate / cm3 time taken for text to not be visible / s 40 45 50 Fig. 2.2

[4]

(c) The relative rate of reaction in each experiment is calculated using the equation shown. relative rate of reaction = 1 time taken

(i) Calculate the relative rate of reaction in Experiment 1.

Do not give units for your answer.

relative rate of reaction = [1]

(ii) State in which Experiment, 1, 2, 3, 4 or 5, the relative rate of reaction was greatest [1] , ,

(d) In each experiment the total volume of aqueous sodium thiosulfate and distilled water is constant.

(i) Calculate the volume of distilled water needed when the volume of aqueous sodium thiosulfate is 37 cm3.

volume = [2]

(ii) From your graph in Fig. 2.2, deduce the time for the text to not be visible when the volume of aqueous sodium thiosulfate is 37 cm3.

Show clearly on Fig. 2.2 how you worked out your answer.

time = s [2]

(iii) Explain why the total volume of aqueous sodium thiosulfate and distilled water is kept constant [1]

(e) (i) State why measuring the volume of the dilute hydrochloric acid with a burette instead of a measuring cylinder would be an improvement [1]

(ii) Explain why it is not possible to use a volumetric pipette to measure the volume of aqueous sodium thiosulfate in each experiment [1]

(f) Explain why it is important not to change the size of the beaker to a larger beaker during the investigation [2]

[Total: 18] , ,

3 A student tests two solids: solid L and solid M.

Tests on solid L

Solid L is hydrated aluminium chloride.

The student dissolves solid L in distilled water to form solution L. Solution L is divided into four approximately equal portions.

(a) To the first portion of solution L, the student adds aqueous sodium hydroxide dropwise and then in excess. observations when added dropwise observations in excess [2]

(b) To the second portion of solution L, the student adds aqueous ammonia dropwise and then in excess. observations when added dropwise observations in excess [2]

(c) To the third portion of solution L, the student adds about 1 cm3 of dilute nitric acid followed by a few drops of aqueous silver nitrate. observations [1]

(d) To the fourth portion of solution L, the student adds about 1 cm3 of dilute nitric acid followed by a few drops of aqueous barium nitrate. observations [1] , ,

Tests on solid M

Table 3.1 shows the tests and the student’s observations for solid M. Table 3.1 tests observations test 1 Do a flame test on solid M. light green coloured flame test 2 Dissolve the remaining solid M in water to form solution M. Divide solution M into three portions. To the first portion of solution M, add about 1 cm3 of aqueous sodium hydroxide. no visible change test 3 To the second portion of solution M, add about 1 cm3 of aqueous sodium hydroxide and a piece of aluminium foil. Warm the mixture and test any gas given off. effervescence is seen; damp red litmus paper turns blue test 4 To the third portion of solution M, add about 1 cm3 of dilute sulfuric acid. white precipitate forms

(e) Identify the gas given off in test 3 [1]

(f) Identify solid M [2]

[Total: 9] , ,