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(a) Method
Read through the method and prepare a table for your results before starting any practical work.
Experiment 1
• Fill the burette labelled FB 1 with the propanone solution, FB 1.
• Fill the second burette with distilled water.
• Run 20.0 cm³ of FB 1 into a 100 cm³ beaker.
• Using a 25 cm³ measuring cylinder, add 20 cm³ of FB 2 to the beaker.
• Using a second 25 cm³ measuring cylinder, measure 10 cm³ of FB 3.
• Add the measured FB 3 to the solution in the 100 cm³ beaker and start timing immediately.
• Stir the mixture once and place the beaker on a white tile.
• Stop timing as soon as the solution goes colourless. Record this reaction time to the nearest second.
• Wash out the beaker thoroughly.
Experiment 2
• Run 14.0 cm³ of FB 1 into the 100 cm³ beaker.
• Run 6.0 cm³ of distilled water into the 100 cm³ beaker.
• Using the measuring cylinder, add 20 cm³ of FB 2 to the beaker.
• Using the second measuring cylinder, measure 10 cm³ of FB 3.
• Add the measured FB 3 to the solution in the 100 cm³ beaker and start timing immediately.
• Stir the mixture once and place the beaker on a white tile.
• Stop timing as soon as the solution goes colourless and record the reaction time as before.
• Wash out the beaker thoroughly.
Experiment 3
Repeat the experiment as before using the volumes below.
• 8.0 cm³ of FB 1
• 12.0 cm³ of distilled water
• 20 cm³ of FB 2
• 10 cm³ of FB 3
Record all your results for experiments 1, 2 and 3 in the space below showing the volume of propanone solution, FB1, the volume of distilled water and the reaction time. [3]
(b) Carry out two experiments to investigate further how the reaction time changes with different concentrations of propanone. Remember that the combined volume of propanone solution and distilled water must always be 20.0 cm³. Record these results in the space below. [2]
(c) (i) Calculate the number of moles of iodine that were added in each experiment.
.................... mol
(ii) Calculate the initial concentration of the iodine in 50 cm³ of the reaction mixture.
initial concentration of iodine = .................. mol dm⁻³ [2]
(d) The rate of the reaction can be represented by the following formula.
'rate' = concentration of iodine from (c)(ii) / reaction time × 10⁵
Use your experimental results to complete the following table to include the reaction time and the 'rate'.
volume of propanone solution, FB1 / cm³
(e) On the grid opposite, plot the 'rate' against the volume of propanone solution, FB1. Draw a line of best fit through the points you have plotted. [8]
(f) (i) From your results what conclusion can you draw about the relationship between the rate of this reaction and the concentration of propanone?
..................................................................................................................
..................................................................................................................
(ii) Suggest an improvement to the experiment that would allow you to be more confident about this conclusion.
..................................................................................................................
.................................................................................................................. [3]
(g) Carry out one additional experiment to investigate how the 'rate' is altered when the concentration of iodine is halved. Record the volume of each solution used and the reaction time in the space below. Calculate the 'rate' using the equation in (d).
'rate' = .................. [2]
(h) From your results in (d) and (g), what conclusion can you draw about the relationship between the rate of reaction and the concentration of iodine?
..................................................................................................................
.................................................................................................................. [1]
(i) In these experiments you used a burette to measure 20.0 cm³ of FB 1. Calculate the percentage error in measuring this volume.
percentage error = ................. [2]
534
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FB 4, FB 5 and FB 6 are aqueous solutions each of which contains a single cation and a single anion. One of these solutions is a dilute acid and this is the only acid present. By carrying out specific tests you will identify all three compounds.
(a) (i) Select a single chemical reagent which would allow you to identify the dilute acid. You may not use indicator paper.
reagent ............................................
(ii) Use this reagent to test all three solutions and record your observations in an appropriate form in the space below.
(iii) From your observations in (ii), identify which solution is the dilute acid.
FB ....................................... is the dilute acid. [4]
(b) The acid you have identified in (a)(iii) is dilute sulfuric acid.
Complete the following table.
[Table_1]
| test | observations |
|---|---|
| To 1 cm depth of FB 4 in a test-tube, add 1 cm depth of FB 5. | |
| To 1 cm depth of FB 5 in a test-tube, add 1 cm depth of FB 6. | |
| To 1 cm depth of FB 6 in a test-tube, add 1 cm depth of FB 4. |
[3]
(c) Test the two remaining unidentified solutions separately with aqueous sodium hydroxide and aqueous ammonia. Record your observations in a suitable form below. You are reminded that if any solution is warmed a boiling tube MUST be used. [4]
(d) From your observations in (a), (b) and (c), identify the ions present in the two solutions tested in (c), giving the relevant evidence for each. If you have not been able to identify one or more of the ions, explain why the evidence obtained was insufficient.
FB ....................................... cation .............................. evidence ..........................
....................................................... anion .............................. evidence ..........................
FB ....................................... cation .............................. evidence ..........................
....................................................... anion .............................. evidence ..........................
[4]
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