36. O/N 2013/P12/Q11
The complete combustion of 20cm3 of a gaseous alkane, X, requires 130 cm3 of oxygen. Both volumes were measured at r.t.p..
What could be the identity of X?
A Butane
B Ethane
C Methane
D Propane
Answer: A
Explaination
First, we need to recall moles, as we know that gas having same moles will have same volume at r.t.p with irrespective of any gas.
For e.g: 1 mole of nitrogen gas = 24dm3 volume
If there is 2 moles of nitrogen gas = 48dm3 volume (volume increase with respect to mole)
If there is 3 moles of nitrogen gas = 72 volume (3 × 24)
So let’s have a look for question:
Alkane (X) + O2 ---------------> CO2 + H2O (alkane combustion)
To find the simplest whole ratio
Now to get this above ratio we need to find out gas X (butane/propane/ethane/methane) which combust at this ratio i.e: 1:6.5
Hence, butane is the gas which combust at 1 : 6.5 ratio.
