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9701/53

Chemistry 9701/53 — May/June 2016

Cambridge A-Level · Planning, Analysis and Evaluation · worked solutions for every part, with the mark scheme

2
questions
30
marks
75
minutes

Topics Analysis, Conclusions and Evaluation · Planning

Q1PlanningAnalysis, Conclusions and EvaluationFree sample

Lithium is a soft alkali metal which may be cut with a knife. It is usually stored under oil because it reacts rapidly with moisture and oxygen in the air.

Lithium is corrosive and may cause burns.

Lithium is highly flammable and in large amounts reacts violently with water.

2Li(s)+2H2O(l)→2LiOH(aq)+H2(g)2\text{Li(s)} + 2\text{H}_2\text{O(l)} \rightarrow 2\text{LiOH(aq)} + \text{H}_2\text{(g)}

This reaction can be used to determine the relative atomic mass of lithium by measuring the volume of hydrogen produced from a small amount of lithium.

(a)

Draw the apparatus you could use to measure the volume of hydrogen produced, using standard laboratory equipment.

Label the chemicals in your diagram and show how the reactants can be kept apart until the reaction is started.

3M
(b)

To successfully carry out this experiment a correct procedure must be followed. The lithium you will use is stored as large pieces under oil.

(i)

Beginning with a large piece of lithium being removed from the oil, state how you would prepare a small piece of lithium for use in this experiment.

1M
(ii)

By only observing the gas collecting apparatus, state how you would know the reaction had stopped.

1M
(iii)

Other than eye protection, state two precautions you would take to make sure that the experiment proceeds safely.

2M
(iv)

The relative atomic mass of lithium is known to be approximately 7.

What approximate volume of hydrogen gas would a 0.1 g mass of lithium produce?

(1 mol of gas occupies 24.0 dm3^3 at room temperature and pressure.)

1M
(v)

What would be the capacity (volume) of the gas collecting apparatus you would use for the volume of hydrogen produced in (iv)?

1M
(c)

Another method that can be used to determine the relative atomic mass of lithium is by titration of the lithium hydroxide produced during its reaction with water.

The following experimental procedure may be used.

  1. Add 100.0 cm3^3 of distilled water to a clean beaker.
  2. Add a known mass of lithium to the distilled water.
  3. After the reaction is complete, transfer 25.0 cm3^3 of the solution of lithium hydroxide from the beaker to a clean conical flask.
  4. Titrate this with an acid of known concentration.
(i)

State how you would accurately measure the total volume of distilled water in step 1.

1M
(ii)

State how you would know that the reaction between lithium and distilled water was complete.

1M
(iii)

State how you would transfer 25.0 cm3^3 of the solution of lithium hydroxide into a clean conical flask in step 3.

1M
(iv)

State how you would ensure that your titration result was reliable.

1M
(d)

To make sure that the beaker and the conical flask used in the experimental procedure in (c) are clean, a student decides to wash them out with some distilled water before starting the experiment.

Some water remains in the beaker. State the effect, if any, this would have on the calculated relative atomic mass of lithium. Explain your reasoning.

Some water remains in the conical flask. State the effect, if any, this would have on the calculated relative atomic mass of lithium. Explain your reasoning.

2M

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