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secondary 3 | A Maths
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Clara
Clara

secondary 3 chevron_right A Maths chevron_right Singapore

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Date Posted: 1 week ago
Views: 19
J
J
1 week ago
Only carbon dioxide and water are formed.

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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Ismail Putra
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