Mole ConceptHard
Question
10 mL of a gaseous hydrocarbon is exploded with 100 mL of oxygen. The residual gas on cooling is found tp measure 95 mL of which 20 mL is absorbed by caustic soda and the remainder by alkaline pyrogallol. The formula of the hydrocarbon is
Options
A.CH4
B.C2H6
C.C2H4
D.C2H2
Solution
CxHy + 
O2 → xCO2 + 
H2O
1 mL
mL x mL 
mL
10 mL 10
mL 10 x mL
Volume absorbed by KOH = Volume of CO2
Volume of CO2 = 20 mL
∴ 10x = 20
x = 2 mL = 2 mol
volume obsorbed by alkaline pyrogallol = volume of O2 = 95 - 20 = 75 mL
Excess of O2 = 75 mL
Total O2 = 100 mL
Volume of O2 reacted = 100 - 75 = 25 mL
∴ 10
= 25 mL
∴ y = 2
Formula of hydrocarbon = C2H2
O2 → xCO2 + H2O1 mL
mL x mL mL10 mL 10
mL 10 x mLVolume absorbed by KOH = Volume of CO2
Volume of CO2 = 20 mL
∴ 10x = 20
x = 2 mL = 2 mol
volume obsorbed by alkaline pyrogallol = volume of O2 = 95 - 20 = 75 mL
Excess of O2 = 75 mL
Total O2 = 100 mL
Volume of O2 reacted = 100 - 75 = 25 mL
∴ 10
= 25 mL∴ y = 2
Formula of hydrocarbon = C2H2
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