Atom, Molecules and stoichiometry

kankanqa

In an experiment, 10 cm3 of a gaseous hydrocarbon were mixed with 225 cm3 of excess air, and the mixture ignited. On cooling to room temperature and pressure, 210cm3 of gases remained, and on shaking with caustic soda(NaOH) solution, the gaseous volume was reduced by 30cm3. Calculated the molecule formula of the hydrocarbon.

abcdefg111

In an experiment, 10 cm3 of a gaseous hydrocarbon were mixed with 225 cm3 of excess air, and the mixture ignited. On cooling to room temperature and pressure, 210cm3 of gases remained, and on shaking with caustic soda(NaOH) solution, the gaseous volume was reduced by 30cm3. Calculated the molecule formula of the hydrocarbon.

let the molecular of hydrocarbo be CxHy
CxHy  +( x+y/4)O2  --> xCO2 +y/2 H2O
10cm3       45cm3            30cm3
so x=3        x+y/4 =4.5  y=1.5*=6
molecular of hydrocarbon is C3H6

kankanqa

don't understand so x=3        x+y/4 =4.5  y=1.5*=6

kankanqa

why O2 has 45cm3?

abcdefg111

don't understand so x=3        x+y/4 =4.5  y=1.5*=6
打錯應該係x+y/4=4.5 y=1.5*4 =6
如果0.01dm3 既CxHy =0.01/24 既mole   CO2 既mole 就係0.03/24
CxHy  +( x+y/4)O2  --> xCO2 +y/2 H2O
mole ratio : 1:x
0.01/24          1
-----------  =   ----
0.03/24          x
所以x=3

abcdefg111

In an experiment, 10 cm3 of a gaseous hydrocarbon were mixed with 225 cm3 of excess air, and the mixture ignited. On cooling to room temperature and pressure, 210cm3 of gases remained, and on shaking with caustic soda(NaOH) solution, the gaseous volume was reduced by 30cm3. Calculated the molecule formula of the hydrocarbon.
O2 remained = 210-30 =180
O2 used =225-180=45