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Detecting atmospheric pollutants: sulfur dioxide
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Health & safety note: small amounts of toxic sulfur dioxide (~ 11 cm ) are
generated in these ‘micro-scale’ reactions. Do not inhale while leaning over the
Petri dish. Anyone suffering from a respiratory problem should check with one of
the CLEAPSS advisers before carrying out this activity.
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¦ Wear eye protection. Avoid inhaling the gas.
¦ Place a 9 cm Petri dish on the solid-line circle (right).
¦ Place the test papers or solutions in the indicated positions as follows*:
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1. Potassium dichromate(VI) paper – slightly damp. Handle with forceps.
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2. Sodium hydroxide solution, 0.01 M containing Full range Universal
indicator (2 drops).
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3. Iodine in potassium iodide solution, 0.01 M (2 drops).
RV
4. Acidified potassium manganate(VII) solution (2 drops).
5. Barium chloride solution, 0.1 M (2 drops).
6. Barium chloride solution, 0.1 M (1 drop) + hydrogen peroxide solution,
20 vol (1 drop).
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¦ To generate the sulfur dioxide add a small spatula measure of sodium
metabisulfite powder (~0.04 g) to the reaction vessel (RV) at the centre of the
Petri dish, followed by 3 drops of 1 M hydrochloric acid.
Immediately put the lid on the Petri dish.
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¦ Record observations over the next 5-10 minutes (eg, by taking photographs
at intervals).
¦ Disposal: once observations are complete - place the Petri dish in a fume
cupboard or immerse in waste container provided.
*Optional: also place test paper/solutions in the matching outer-ring circles (i.e.
outside the Petri dish) – you can then compare these with those inside the Petri
dish to see what effect the sulfur dioxide has.
ASE 01/14_DRAFT
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