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Need help for CIE A level chemistry

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The answer for this question is D. Why isn't it A? In my opinion, according to this equation, CxHy + (x + y/4)O2 ---> xCO2 + (y/2)H20, the volume of residual gas of butane would be the highest instead of methane?

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Reply 3

n.safar4

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Let's consider methane first.
When you balance the equation, you realise that you have 1 mol of CO2 (10cm^3) and 2 moles of h2o (20cm^3) overall giving 30 cm^3. However, you need to add the remaining volume of oxygen which didn't react since oxygen was in excess. This is 30cm^3, altogether adding up to 60.

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