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(a) Method
Experiment 1
• Fill the burette labelled FB 1 with FB 1.
• Run 20.00 cm3 of FB 1 into a 100 cm3 beaker.
• Using the measuring cylinder add the following to the second 100 cm3 beaker:
◦ 10 cm3 of FB 2
◦ 20 cm3 of FB 3
◦ 10 cm3 of FB 4
• Add the contents of the first beaker to the second beaker and start timing immediately.
• Stir the mixture once and place the beaker on a white tile.
• Stop timing as soon as the solution turns blue-black. Ignore any colour changes that occur before the intense blue-black colouration.
• Record this reaction time to the nearest second in the space provided on page 4.
• Rinse both beakers and shake dry. Rinse and dry the glass rod.
Experiment 2
• Fill a second burette with distilled water.
• Run 10.00 cm3 of FB 1 into a 100 cm3 beaker.
• Run 10.00 cm3 of distilled water into the same beaker containing FB 1.
• Using the measuring cylinder add the following to the second 100 cm3 beaker:
◦ 10 cm3 of FB 2
◦ 20 cm3 of FB 3
◦ 10 cm3 of FB 4
• Add the contents of the first beaker to the second beaker and start timing immediately.
• Stir the mixture once and place the beaker on a white tile.
• Stop timing as soon as the solution turns blue-black. Ignore any colour changes that occur before the intense blue-black colouration.
• Record this reaction time to the nearest second in the space provided on page 4.
• Rinse both beakers and shake dry. Rinse and dry the glass rod.
Experiments 3–5
• Carry out three further experiments to investigate how the reaction time changes with different volumes of FB 1.
Remember that the combined volume of FB 1 and distilled water must always be 20.00 cm3.
Do not carry out an experiment using 15.00 cm3 of FB 1.
Do not use a volume of FB 1 that is less than 5.00 cm3.
Keep all FB labelled solutions for use in (e) and in Question 2.
Record all your results in a single table. You should include the volume of FB 1, the volume of distilled water and the reaction time.
The relative rate for the reaction is given by the following expression.
$$\text{relative rate} = \frac{1000}{\text{reaction time in seconds}}$$
Use this expression to calculate the relative rate for each of your experiments and record the values in your results table.
(b) On the grid opposite, plot the relative rate against the volume of FB 1. Include the origin in your plot. Label any points you consider anomalous. Draw a line of best fit.
(c) From your graph, what conclusion can you make about the relationship between the relative rate for the reaction and the volume of FB 1 used? Explain your answer.
(d) A student carried out the same experiment but used 15.00 cm3 of FB 1. The student recorded a value for the reaction time of 28 s.
(i) Use your graph to calculate the time you would have expected to record if you had carried out an experiment using 15.00 cm3 of FB 1.
Show the construction lines on your graph and show your working in the calculation.
reaction time = .............................. s
[2 marks]
(ii) Calculate the percentage difference between your value and that of the student.
Show your working.
percentage difference = .............................. %
[1 mark]
(e) You are to carry out a sixth experiment. The concentrations of iron(III) chloride, sodium thiosulfate and starch indicator should all be the same as in Experiment 2 but the concentration of iodide ions should be twice the value that it is in Experiment 2. State the volume of each solution used and record the reaction time to the nearest second.
(f) (i) 20.00 cm3 of 0.0500 mol dm-3 FeCl3, FB 1, were reacted with excess KI, FB 2.
Using the information on page 2, calculate the number of moles of I2 produced.
moles I2 = .............................. mol
[2 marks]
(ii) The iodine produced in (i) required 35.00 cm3 of a different solution of sodium thiosulfate for complete reaction.
Calculate the concentration of the solution of sodium thiosulfate used.
concentration of Na2S2O3 = .............................. mol dm-3
[1 mark]
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(a) $FB\ 1$ is aqueous acidified iron(III) chloride, $FeCl_3$.
$FB\ 5$ is $0.150 \text{ mol dm}^{-3}$ sodium thiosulfate, $Na_2S_2O_3$.
(i) Carry out the following tests and record your observations.
[Table_1]
To a $1 \text{ cm depth of } FB\ 1$ in a test-tube add a $1 \text{ cm depth of } FB\ 5$. Leave to stand until there is no further change, then
add aqueous sodium hydroxide.
To a $1 \text{ cm depth of } FB\ 5$ in a test-tube add a few drops of dilute hydrochloric acid. Leave to stand. Rinse the tube thoroughly.
(ii) In (i) you should have observed a reaction between $Fe^{3+}(aq)$ and $S_2O_3^{2-}(aq)$.
Do you think that this reaction affected your results in Question 1? Refer to the equations on page 2. Explain your answer.
(b) $FB\ 6$ is a solution containing a halide ion.
(i) Carry out the following tests and record your observations.
[Table_2]
To a $1 \text{ cm depth of } FB\ 6$ in a test-tube add aqueous silver nitrate, then
add aqueous ammonia.
To a $1 \text{ cm depth of } FB\ 6$ in a test-tube add aqueous silver nitrate, then
add $FB\ 5$.
(ii) The halide in $FB\ 6$ is $\text{.......................}$ .
(c) $FB\ 7$ is a solution of copper(II) sulfate, $CuSO_4$.
(i) Carry out the following tests and record your observations.
[Table_3]
To a $1 \text{ cm depth of } FB\ 7$ in a test-tube add a $1 \text{ cm depth of } FB\ 2$, $KI$, then
add $FB\ 4$, starch indicator.
To a $1 \text{ cm depth of } FB\ 7$ in a test-tube add a $1 \text{ cm depth of } FB\ 5$, then
add a $1 \text{ cm depth of } FB\ 2$ followed by $FB\ 4$, starch indicator.
(ii) Give the formula of one of the products formed in the reaction of $FB\ 7$ with $FB\ 2$ in the first test. $\text{.....................................................}$
(d) $FB\ 8$ is a solution of a salt containing one cation and one anion from those listed in the Qualitative Analysis Notes.
The cation in $FB\ 8$ is one of $Mg^{2+}$, $Zn^{2+}$ or $Al^{3+}$.
The anion in $FB\ 8$ is either $SO_3^{2-}$ or $SO_4^{2-}$.
(i) Select reagents and carry out tests to identify which ions are present in $FB\ 8$. Give details of your tests and observations.
(ii) The formula of $FB\ 8$ is $\text{.......................}$ .
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