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Question
secondary 3 | A Maths
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Why
The options indicate that the gas contains carbon and hydrogen atoms only.
In other words, it is a hydrocarbon.
Let the chemical formula of the hydrocarbon be CxHy.
Write the chemical equation, keeping in view that CxHy ≡ 5 O2
CxHy + 5O2 → y/2 H2O + xCO2
The equation must be balanced. Number of oxygen atoms on both sides must be the same.
5 × 2 = y/2 × 1 + x × 2
10 = ½y + 2x
20 = y + 4x
y = 20 - 4x
Now the options indicate that the gas is an alkane. Remember that alkanes have general formula CnH(2n+2)
So y = 2x + 2
Solving for x,
20 - 4x = 2x + 2
6x = 18
x = 3
y = 2(3) + 2 = 8
C3H8 (propane) is the answer.
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