Question

100 g of a hydrocarbon \(C_xH_y\) is completely burnt to produce 130 g of \(H_2O\). The produced carbon dioxide can use 228.56 g of \(O_2\) via photosynthesis. What is the molecular formula of the hydrocarbon?

• A. \(C_2H_4\)
• B. \(C_4H_8\)
• C. \(C_2H_6\)
• D. \(C_4H_{10}\)

Hint:

In combustion problems, always use \(H_2O\) to find hydrogen and \(O_2/CO_2\) balance to find carbon.

Answer 1

The Correct Option is B

Step 1: Hydrogen determination from water.
130 g H₂O = 130/18 ≈ 7.22 mol; H atoms = 14.44 mol.

Step 2: Hydrogen content in hydrocarbon.
The 100 g hydrocarbon supplies 14.44 mol of H atoms, constraining the H count in C_xH_y.

Step 3: Carbon estimation via oxygen consumption.
228.56 g O₂ = 228.56/32 ≈ 7.14 mol, used for complete combustion to CO₂ and H₂O, enabling carbon calculation.

Step 4: Deriving the empirical ratio.
Balancing C and H from combustion data leads to a C:H ratio matching C₄H₈.

Step 5: Verification against options.
Only C₄H₈ satisfies both hydrogen and oxygen balance under the given combustion constraints.