AS & A Level Chemistry - 9701 Paper 5 2011 Winter Zone 3

You are to plan an experiment to investigate how the rate of effusion depends on the relative molecular mass, $M_r$, of a gas.

(a) At a constant temperature, the rate of effusion of a gas depends on the kinetic energy of the molecules of the gas. So, for a series of gases all at the same temperature, as the $M_r$ of a gas increases the speed of the molecules of the gas decreases.

(i) Predict how the rate of effusion will change as the $M_r$ of the gas increases. Explain your prediction using the information in part (a) above.

prediction .................................................................
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(ii) Display your prediction in the form of a sketch graph below, clearly labelling the axes.

[3]

(b) In the experiment you are about to plan, identify the following.

(i) the independent variable ..................................................
(ii) the dependent variable ....................................................
[2]

(c) Using the apparatus shown below design a laboratory experiment to test your prediction in (a).
In addition to the standard apparatus present in a laboratory you are provided with the following materials,
\bullet access to samples of the following gases; hydrogen, oxygen, carbon dioxide, butane and chlorine,
\bullet a stop watch/clock.

Describe how you would carry out the experiment. You should
\bullet ensure that the volume of gas measured is the same for each experiment,
\bullet ensure that the syringe contains only the gas under investigation,
\bullet ensure that the syringe is used under the same conditions throughout all of the experiments,
\bullet measure the effusion time,
\bullet produce reliable results.
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(d) State a hazard that must be considered when planning the experiment and describe precautions that should be taken to keep risks to a minimum.
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[2]

(e) Draw a table with appropriate headings to show the data you would record when carrying out your experiments and the values you would calculate in order to construct a graph to support or reject your prediction in (a). The headings must include the appropriate units. Ensure that the table covers all the detail relating to the five gases listed in (c).
$[A_r: H, 1.0; C, 12.0; O, 16.0; Cl, 35.5]$
[2]

There are three oxides of lead, PbO, PbO_2 and Pb_3O_4 all of which can be reduced to metallic lead by hydrogen. A sample of one of these oxides is reduced to find out which of the three oxides it is.
An experiment was carried out as follows.
• An empty reduction tube was weighed and the mass recorded.
• A sample of the lead oxide was added to the reduction tube and the new mass recorded.
• The reduction tube and lead oxide was heated strongly for five minutes in a stream of hydrogen and then allowed to cool back to room temperature.
• The reduction tube and contents were then reweighed and the mass recorded.
(a) The results of several such experiments are recorded below.
[$A_r$: O, 16.0; Pb, 207.0]
Process the results in the table to calculate the number of moles of lead atoms and the number of moles of oxygen atoms.
Record these values in the additional columns of the table. You may use some or all of the columns. Label the columns you use.
Masses should be recorded to two decimal places while the number of moles should be recorded to two significant figures.
For each column you use include units where appropriate and an expression to show how your values are calculated.
You may use the column headings A to G for these expressions (e.g. A–B). [3]