A sample of water from a stream, suspected to be contaminated with metal ions, was analysed - HSC - SSCE Chemistry - Question 10 - 2010 - Paper 1
Question 10
A sample of water from a stream, suspected to be contaminated with metal ions, was analysed.
The results of some tests on the water are recorded in the table.
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Worked Solution & Example Answer:A sample of water from a stream, suspected to be contaminated with metal ions, was analysed - HSC - SSCE Chemistry - Question 10 - 2010 - Paper 1
Step 1
Add dilute HCl: No change
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Answer
The lack of reaction indicates that no soluble carbonate or sulfide ions are present in the water sample.
Step 2
Add Na2SO4 solution: White precipitate formed
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Answer
The formation of a white precipitate suggests the presence of barium ions (Ba²⁺) or lead ions (Pb²⁺), as they form insoluble sulfates. Based on the options given, Ba²⁺ is one of the candidates.
Step 3
Flame test: Pale green colour
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A pale green flame indicates the presence of barium ions (Ba²⁺), as barium produces a green flame during the flame test.
Step 4
Conclusion
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Answer
Taking into account the results of all tests, the most likely contaminant in the water is Ba²⁺.
