10 cm3 of a gaseous hydrocarbon, CxHy, was reacted with 100 cm3 of oxygen gas, an excess. The final volume of the gaseous mixture was 95 cm3. This gaseous mixture was treated with concentrated, aqueous sodium hydroxide to absorb the carbon dioxide present. This reduced the gas volume to 75 cm3. All gas volumes were measured at 298K and 100 kPa.

(i) Balance the equation below
............CxHy + ............O2  ............CO2 + zH2O
(ii) Calculate the values of x,y and z

Question

10 cm3 of a gaseous hydrocarbon, CxHy, was reacted with 100 cm3 of oxygen gas, an excess. The final volume of the gaseous mixture was 95 cm3. This gaseous mixture was treated with concentrated, aqueous sodium hydroxide to absorb the carbon dioxide present. This reduced the gas volume to 75 cm3. All gas volumes were measured at 298K and 100 kPa. 

(i) Balance the equation below
............CxHy + ............O2  ............CO2 + zH2O 
(ii) Calculate the values of x,y and z

cuanchi · Answer

convert the pressure 100 kPa to atm
With the volume (10 cm3) of the gaseous hydrocarbon, the temperature and pressure (PV=nRT) you can calculate the "n" of gaseous hydrocarbon.
In a similar way with ( 75 cm3) you can calculate the moles of H2O, and with the difference 95-75cm3 the moles of CO2.
Then divide the 3 values for the smallest one of the three, and that would be the coefficients in the chemical equation. 
Based in the number of moles of CO2 you can divide that value by the coefficient in the CxHy to find "x" and the number of moles of H2O times 2 and divided by the coefficient of CxHy will give you the "y".
If "x" or "y" are not round numbers, divide both for the smallest one. If still the other is not a integer number multiply both for the same factor until both are round numbers.