butane in a limited amount of oxygen

Question

A 30cm3 sample of butane, C4H10, was completely reacted in a limited supply of oxygen to produce 60 cm3 of carbon dioxide and 60 cm3 of carbon monoxide.
All volumes were measured at room temperature and pressure.
Which volume of oxygen was used?

A 90cm3 B 120cm3 C 150cm3 D 165cm3

(answer D, but why?)

Answer 1

Write the balanced equation for this combustion reaction noting that that CO and CO2 that are produced are in equal amounts (60 ml) so are in 1:1 ratio in the balanced equation.

2 C4H1O + 11 O2 ===> 4 CO2 + 4 CO + 10 H2O

 

Now, simply solve for the 11 oxygens as a volume, given that you started with 30 cm³ of butane:

30 cm³ butane x 11 cm³ O2/2 cm³ butane = 165 cm³ O2

 

NOTE:  In this type of problem, the volume are equivalent to moles, so in the balanced equation, the coefficients can be viewed as moles, cm³, liters, etc.