chlorine tablet cover water damp litmus paper extraction vent test chamber Table 1 gives observations made during a safety check at an indoor swimming pool....
Question 1 Report
Table 1 gives observations made during a safety check at an indoor swimming pool. A worker dissolves a chlorine-releasing tablet in water inside a covered test chamber. Air from above the water is drawn slowly through a tube onto a small strip of damp blue litmus paper. Fig. 1 shows the test chamber after two minutes. The manager wants to confirm that the ventilation system removes chlorine gas before staff enter the plant room. Chlorine is a poisonous gas, so the test is done with only a small sample and the chamber remains closed. The pH of the water is also recorded because chlorine compounds can make an acidic solution.
| Observation | Result |
|---|---|
| Colour of damp blue litmus after 10 s | red |
| Colour of the same paper after 2 min | white |
| pH of water in chamber | 4 |
(a) Describe the colour changes shown by the litmus paper in Table 1. [2]
(b) Give the name of the gas indicated by these results. [1]
(c) Use the pH value to state whether the water is acidic, neutral or alkaline. [1]
(d) Describe one safety precaution, other than keeping the chamber closed, that the worker should use when preparing the chlorine solution. [2]
(e) Describe why dry blue litmus paper would be less suitable for this test. [2]
(f) Give one reason why the ventilation system should be checked before staff enter the plant room. [2]
Answer Details
(a) Damp blue litmus changes to red, then the red colour changes to white because it is bleached. [2]
(b) These results indicate chlorine. [1]
(c) A pH of 4 is acidic. [1]
(d) Wear eye protection to prevent splashes of chlorine solution reaching the eyes. Wearing gloves to avoid skin contact, or preparing the solution in a fume cupboard or well-ventilated area to avoid breathing chlorine, are also acceptable. [2]
(e) Water is needed for chlorine to dissolve and react. Dry blue litmus may show no colour change, or a much slower change. [2]
(f) Chlorine gas is toxic and harmful if inhaled. Ventilation must remove it and prevent a dangerous build-up before staff enter. [2]
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