a)
| Material (M) | Apparatus (A) |
|
|
b) Well water – 40 min
Pond water – 25 min
River water – 15 min
ci) Observation 1 : The time taken for methylene blue solution in well water sample to decolorize is 40 minutes.
Observation 2 : The time taken for methylene blue solution in river water sample to decolorize is 15 minutes.
ii) Inference 1 : The time taken for methylene blue solution in well water sample to decolorize is longest because it has a high concentration of dissolved oxygen//less polluted//less microorganism.
Inference 2 : The time taken for methylene blue solution in river water sample to decolorize is shortest because it has a low concentration of dissolved oxygen//more polluted//more microorganism.
d)
| Variable | Method to handle the variable |
| Manipulated variable Water sample |
Use different water sample, well water, pond water, river water |
| Responding variable Time taken for the methylene blue solution to decolourise | Record the time taken for the methylene blue solution to decolourise using a stopwatch |
| Constant variable Volume / concentration of methylene blue solution// Volume of water sample
|
Fix the volume of methylene blue solution at 1ml// Fix the concentration of methylene blue solution at 0.1% Fix the volume of water sample at 100 ml |
e) The shorter time the taken for the methylene blue solution to decolorize, the more polluted the water sample.
f)
| Water sample | Time taken for the methylene blue solution to decolourise (minutes) | Level of water pollution |
| Well water | 40 | Less polluted |
| Pond water | 25 | Moderately polluted |
| River water | 15 | Very polluted |
g) The shorter time the taken for the methylene blue solution to decolorize, the higher the level of water pollution of the water sample. The number of bacteria in water sample is high. More oxygen is used to decompose organic substances in water sample.
h) Less than 15 minutes ………… oxygen ………..pollutants
i) ………time taken to decolorize ……….. sources of water sample.
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