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mole fraction exam question pl help

its a multiple choice question with no data given
the mole fraction of butane in a mixture of butane and o2 with the minimum amount of o2 required for complete combustion is
a0.133
b0.153
c0.167
d0.200
the answers A but I don't get how u do it wiith no data except the comlete cubustion equation of butane
c4h10 + 6.5o2 ----> 4co2 + 5h2o
do u even need to work anything out or do u just choose the lowest number from the choices given
Original post by usernamenew
its a multiple choice question with no data given
the mole fraction of butane in a mixture of butane and o2 with the minimum amount of o2 required for complete combustion is
a0.133
b0.153
c0.167
d0.200
the answers A but I don't get how u do it wiith no data except the comlete cubustion equation of butane
c4h10 + 6.5o2 ----> 4co2 + 5h2o
do u even need to work anything out or do u just choose the lowest number from the choices given

The question, and the equation betweeen them give you all the data you need.

You are told the mixture is butane and oxygen, so you can ignore the possibility of anything else being present.
You are also told you have the minimum amount of oxygen required for complete combustion of the butane is present. In other words the oxygen and butane are in the exact ratio of the chemical equation - 1:6.5

So, if you have x moles of butane, you must have 6.5x moles of oxygen. The total numbr of moles of gas is 7.5x (i.e. x + 6.5x).
The molar fraction of butane is (number of moles butane) / (total number of moles of gases) or
x / (7.5x)

As an example, if we assume we have 1 mole of butane, x=1. the molar fraction is 1/(7.5) = 0.133.
You get the same answer for any other value of x - try it.

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