Step 1: Calculate the moles of carbon dioxide (CO2) produced.
At standard temperature and pressure (STP), 1 mole of any gas occupies 22.4dm3.
Given volume of CO2=89.6dm3.
nCO2=MolarvolumeatSTPVolumeofCO2
nCO2=22.4dm3/mol89.6dm3=4 mol
Step 2: Calculate the moles of water (H2O) produced.
The molar mass of H2O is 2×1.008g/mol(H)+16.00g/mol(O)=18.016g/mol≈18 g/mol.
Given mass of H2O=54 g.
nH2O=MolarmassofH2OMassofH2O
nH2O=18g/mol54g=3 mol
Step 3: Determine the moles of carbon (C) and hydrogen (H) atoms in the hydrocarbon.
From the complete combustion of a hydrocarbon, all carbon atoms form CO2 and all hydrogen atoms form H2O.
Each mole of CO2 contains 1 mole of C atoms.
Moles of C atoms = nCO2=4 mol
Each mole of H2O contains 2 moles of H atoms.
Moles of H atoms = 2×nH2O=2×3mol=6 mol
Step 4: Determine the molecular formula of the hydrocarbon.
The ratio of carbon atoms to hydrogen atoms in the hydrocarbon is 4:6.
This simplifies to 2:3.
So, the empirical formula is C2H3.
Let the general formula of the hydrocarbon be CxHy.
From the moles of C and H atoms, we have x=4 and y=6.
Therefore, the molecular formula of the hydrocarbon is C4H6.
Step 5: Classify the hydrocarbon.
The general formula for alkanes is CnH2n+2. For n=4, this would be C4H10.
The general formula for alkenes is CnH2n. For n=4, this would be C4H8.
The general formula for alkynes or dienes is CnH2n−2. For n=4, this would be C4H2(4)−2=C4H6.
Thus, the hydrocarbon is an alkyne or a diene.
The final answer is C4H6.