Chemistry 9701/34 — May/June 2018

Cambridge AS Level · Advanced Practical Skills · worked solutions for every part, with the mark scheme

questions

marks

120

minutes

Topics Manipulation, Measurement and Observation · Presentation of Data and Observations · Analysis, Conclusions and Evaluation · Qualitative Analysis

Q1Manipulation, Measurement and ObservationPresentation of Data and ObservationsAnalysis, Conclusions and EvaluationFree sample

Glucose, $\text{C}_6\text{H}_{12}\text{O}_6$ , is a sugar that can act as a reducing agent. You will investigate how an increase in temperature affects the rate of the redox reaction between glucose and acidified potassium manganate(VII).

FB 1 is $0.010\text{ mol dm}^{-3}$ acidified potassium manganate(VII), $\text{KMnO}_4$ .
FB 2 is $1.0\text{ mol dm}^{-3}$ sulfuric acid, $\text{H}_2\text{SO}_4$ .
FB 3 is an aqueous solution containing $32.8\text{ g dm}^{-3}$ glucose, $\text{C}_6\text{H}_{12}\text{O}_6$ .
distilled water

You will measure the time it takes for the purple colour to disappear. Your table of results on page 4 should include the rate of reaction for each experiment.

(a)

Method

Experiment 1

Fill the burette with FB 1.
Add $10.00\text{ cm}^3$ of FB 1 into the $250\text{ cm}^3$ beaker.
Use the $50\text{ cm}^3$ measuring cylinder to transfer $50.0\text{ cm}^3$ of FB 2 into the beaker containing FB 1.
Use the same measuring cylinder to transfer $50.0\text{ cm}^3$ of distilled water into the same beaker.
Place the beaker on the tripod and heat its contents to between $65^\circ\text{C}$ and $70^\circ\text{C}$ .
While the solution in the beaker is heating pour $25.0\text{ cm}^3$ of FB 3 into the $25\text{ cm}^3$ measuring cylinder.
When the temperature of the contents of the beaker has reached between $65^\circ\text{C}$ and $70^\circ\text{C}$ , remove the Bunsen burner and carefully place the hot beaker onto the white tile.
Record the temperature of the solution in the beaker.
Add the $25.0\text{ cm}^3$ of FB 3 and immediately start timing.
Stir the contents of the beaker once and stop timing as soon as the solution turns colourless. Record the time to the nearest second.
Record the temperature of the solution as soon as it is colourless.
Calculate and record the average temperature of the reaction mixture to one decimal place.
Empty, rinse and dry the beaker so it is ready for use in Experiment 2.

Experiment 2

Add $10.00\text{ cm}^3$ of FB 1 into the $250\text{ cm}^3$ beaker.
Use the $50\text{ cm}^3$ measuring cylinder to transfer $50.0\text{ cm}^3$ of FB 2 into the beaker containing FB 1.
Use the same measuring cylinder to transfer $50.0\text{ cm}^3$ of distilled water into the same beaker.
Place the beaker on the tripod and heat its contents to between $30^\circ\text{C}$ and $35^\circ\text{C}$ .
While the solution in the beaker is heating pour $25.0\text{ cm}^3$ of FB 3 into the $25\text{ cm}^3$ measuring cylinder.
When the temperature of the contents of the beaker has reached between $30^\circ\text{C}$ and $35^\circ\text{C}$ , remove the Bunsen burner and carefully place the hot beaker onto the white tile.
Record the temperature of the solution in the beaker.
Add the $25.0\text{ cm}^3$ of FB 3 and immediately start timing.
Stir the contents of the beaker once and stop timing as soon as the solution turns colourless. Record the time to the nearest second.
Record the temperature of the solution as soon as it is colourless.
Calculate and record the average temperature of the reaction mixture to one decimal place.
Empty, rinse and dry the beaker so it is ready for use in Experiment 3.

Experiments 3, 4 and 5

Repeat the method for Experiment 2 at three different temperatures.
Keep the temperature of the contents of the beaker between room temperature and $70^\circ\text{C}$ .
Record all your results in your table.

Results

The rate of reaction can be calculated as shown.

\text{rate} = \frac{1000}{\text{reaction time}}

Calculate the rate of reaction for each experiment and include this in your table.

(b)

Plot a graph of rate ( $y$ -axis) against average temperature ( $x$ -axis) on the grid opposite. Select a scale on the $x$ -axis to include an average temperature of $15.0^\circ\text{C}$ . Label any points you consider anomalous.

Draw a line of best fit and extrapolate it to $15.0^\circ\text{C}$ .

Graph Grid

(c)

Use your graph to calculate the time to the nearest second that the reaction would have taken if the average temperature had been $52.5^\circ\text{C}$ .

Show on the grid how you obtained your answer.

(d)

Explain, by referring to your graph or your table of results, how the rate of reaction is affected by an increase in temperature.

(e)

(i)

Calculate the concentration of glucose in FB 3 in $\text{mol dm}^{-3}$ .

(ii)

Under certain conditions, $1.0\text{ mole}$ of acidified potassium manganate(VII), $\text{KMnO}_4$ , can oxidise $2.5\text{ moles}$ of glucose.

Calculate the volume of $0.010\text{ mol dm}^{-3}$ acidified $\text{KMnO}_4$ that would react with all the glucose present in $25.0\text{ cm}^3$ of FB 3.

(iii)

The formula of glucose can be written as $\text{CHO}(\text{CHOH})_4\text{CH}_2\text{OH}$ .

Suggest the formula of an organic product of the oxidation of glucose.

(f)

(i)

Calculate the maximum percentage error in the reaction time recorded for Experiment 1. Assume the error of the timer is $\pm 1\text{ s}$ .

(ii)

You have carried out experiments at five different temperatures.

Identify an experiment, if any, you should have repeated. Give a reason for your answer.

(g)

Suggest two ways to improve the accuracy of the results for this investigation.

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