Pang Wen Ni's answer to Irene's Secondary 4 Biology Singapore question.

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Pang Wen Ni
Pang Wen Ni's answer
2 answers (Tutor Details)
Because when you prepare the set up you turn the cylinder over to submerge it in the water and the gas trapped inside is the air around us. After collection the gas in the cylinder would contain both gas Y and gases present in the air such as oxygen, so it would not be pure gas Y.