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(a) Experiment 1
• Fill a burette with FB 3.
• Use the measuring cylinder labelled A to place 25 cm³ of FB 2 and 25 cm³ of distilled water into a conical flask.
• Add to the conical flask 10.00 cm³ of FB 3 from the burette and 6 drops of starch indicator.
• Use the measuring cylinder labelled B to place 50 cm³ of FB 1 and 20 cm³ of FB 4 into a 100 cm³ beaker.
• Pour the mixture from the beaker into the conical flask and immediately start timing.
• Swirl the flask to ensure good mixing and place the flask on a white tile.
• Stop timing when a blue-black colour suddenly appears in the solution.
• Record, in the table on page 4, the reaction time, in seconds, to the nearest second.
• Empty, rinse and drain the conical flask.
Experiment 2
• Use the measuring cylinder labelled A to place 25 cm³ of FB 2 and 35 cm³ of distilled water into a conical flask.
• Add to the conical flask 10.00 cm³ of FB 3 from the burette and 6 drops of starch indicator.
• Use the measuring cylinder labelled B to place 40 cm³ of FB 1 and 20 cm³ of FB 4 into a 100 cm³ beaker.
• Pour the mixture from the beaker into the conical flask and immediately start timing.
• Swirl the flask to ensure good mixing and place the flask on a white tile.
• Stop timing when a blue-black colour suddenly appears in the solution.
• Record, in the table on page 4, the reaction time, in seconds, to the nearest second.
• Empty, rinse and drain the conical flask.
Experiments 3 - 5
Carry out experiments 3 - 5 in the same way but using the volumes of solutions shown in the table. Complete the units in the table.
Calculate all values of $$\frac{1000}{\text{(reaction time)}}$$ to three significant figures.
[Table_1]
(b) The rate of reaction can be represented by the following formula.
'rate' = $$\frac{1000}{\text{(reaction time)}}$$
On the next page plot a graph of 'rate' against the volume of FB 1.
Start each of the axes at zero.
Draw the line of best fit.
[Graph Paper]
(c) The concentration of hydrogen peroxide in FB 1 is 0.23 mol dm⁻³.
The total volume of each reaction mixture is 130 cm³.
(i) Calculate the initial concentration of hydrogen peroxide for each of the following experiments. Show your working.
[Table_2]
(ii) Use your results in (i) to show that the initial concentration of hydrogen peroxide is directly proportional to the volume of FB 1 used in the experiment.
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(d) A website states that the rate of reaction between acidified hydrogen peroxide and potassium iodide is directly proportional to the concentration of hydrogen peroxide.
Use your graph to decide whether the statement on the website is correct or not.
Explain your answer.
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(e) Experiment 1 was repeated using 0.025 mol dm⁻³ sodium thiosulfate instead of FB 3.
Suggest how this would affect the reaction time.
Explain your answer using the chemical equations on page 3.
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(f) Suggest a factor, other than volumes of solutions used, that could have significantly affected the rate of reaction in each of the experiments.
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(g) A student carrying out a similar investigation decides to repeat one of the experiments a number of times. The reaction times for these repeated experiments are listed below.
[Table_3]
(i) From these experimental results calculate an appropriate mean reaction time, correct to 1 decimal place.
mean reaction time = ............ s
(ii) Assume that the uncertainty in the mean reaction time is ± 2 seconds. Calculate this uncertainty as a percentage of the mean reaction time.
percentage uncertainty = .............. %
(h) The experimental method you have used can be adapted to investigate how the rate of reaction would vary if the concentration of potassium iodide or the concentration of sulfuric acid were changed.
In the first line of the tables below, the volumes of FB 2, distilled water, FB 3, FB 1 and FB 4 used in Experiment 2 are recorded.
Complete the following table, suggesting volumes for each of the reagents that could be used in a further experiment to investigate how the rate of reaction varies with a change in the volume of potassium iodide, FB 2.
Do not carry out this experiment.
[Table_4]
Complete the following table, suggesting volumes for each of the reagents that could be used in a further experiment to investigate how the rate of reaction varies with a change in the volume of sulfuric acid, FB 4.
Do not carry out this experiment.
[Table_5]
528
578
535
(a) Carry out the following tests on FB 5, FB 6 and FB 7 using aqueous sodium hydroxide.
● To 1 cm depth of FB 5, FB 6 and FB 7 in separate boiling tubes add 1 cm depth of aqueous sodium hydroxide.
● Shake the tube to mix the solutions then add a further 2 cm depth of aqueous sodium hydroxide.
● If no precipitate has formed in a solution for either of the previous steps, carefully warm the boiling tube and its contents.
Care: if solutions containing sodium hydroxide are heated too strongly they may be ejected from the tube.
Record your results in an appropriate form in the space below.
(b) Carry out the following tests on FB 5, FB 6 and FB 7 using aqueous ammonia.
● To 1 cm depth of FB 5, FB 6 and FB 7 in separate test-tubes add 1 cm depth of aqueous ammonia.
● Shake the tube to mix the solutions then add a further 2 cm depth of aqueous ammonia.
● Record your results in an appropriate form in the space below.
(c) From your observations in (a) and (b), identify the cation present in each of the following solutions.
\n\n
| solution | cation |
|---|---|
| FB 5 | |
| FB 6 | |
| FB 7 |
(d) Each of the solutions FB 5, FB 6 and FB 7 contains either a sulfate or a sulfite anion.
(i) Which single reagent, when added to the solution, could confirm that either a sulfate or a sulfite is present?
Which additional reagent, when added to the same test-tube, would identify which of these two ions is present?
(ii) Carry out the tests on FB 5, FB 6 and FB 7 using the reagents you have selected and record your observations in the table below.
| observation | FB 5 | FB 6 | FB 7 |
|---|---|---|---|
| reagent used: | |||
| followed by: |
(iii) Identify the anion present in each solution. Explain your answer.
(e) Carry out the following test.
| test | observation |
|---|---|
| To 1 cm depth of FB 5 in a boiling tube, add 2 cm depth of the aqueous hydrogen peroxide, FB 9. Warm the tube, then, ............................................................................................................................... add 2 cm depth of aqueous sodium hydroxide. |
(f) Divide the sample of solid FB 8 in two. Use one portion in each of the following tests.
Test 1
● Place the portion of FB 8 in a boiling tube.
● Add 2 cm depth of dilute sulfuric acid.
● Warm with a Bunsen burner.
● Test any vapour evolved with litmus paper.
Observation ...............................................................................................................
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Test 2
● Reheat the water bath to boiling, then turn off the Bunsen burner.
● Place the remaining FB 8 in a dry test-tube.
● Add 2 cm depth of ethanol.
● Use a dropping pipette to add 2–3 drops of concentrated sulfuric acid.
Care – concentrated sulfuric acid is very corrosive.
● Warm the tube in the hot-water bath.
● After 3–4 minutes of warming tip the contents of the test-tube into a 100 cm3 beaker, ¾ full of cold water.
● Cautiously smell the contents of the beaker.
Observation ...............................................................................................................
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Use your observations above to suggest the type of compound present in FB 8.
597
527
518
