Question

25 g of an unknown hydrocarbon upon burning produces 88 g of CO₂ and 9 g of H₂O. This unknown hydrocarbon contains:
1. 20 g of carbon and 5 g of hydrogen
2. 22 g of carbon and 3 g of hydrogen
3. 24 g of carbon and 1g of hydrogen
4. 18 g of carbon and 7g of hydrogen

Answer 1

Correct Answer - Option 3 : 24 g of carbon and 1g of hydrogen

Calculation:

Let the hydrocarbon is C_xH_y

\({{\rm{C}}_{\rm{x}}}{{\rm{H}}_{\rm{y}}} + {{\rm{O}}_2} \to {\rm{xC}}{{\rm{O}}_2} + \frac{{\rm{y}}}{2}{\rm{\;}}{{\rm{H}}_2}{\rm{O}}\)

Mole of water H₂O = 18.01528 g/mol

Mole of carbon dioxide CO₂ = 44.01 g/mol

Weight of hydrogen (H) = 1.00784 u

Weight of carbon (C) = 12.0107 u

Weight of carbon = \(\frac{{88}}{{44}} \times 12 = 24\;g\)

Weight of Hydrogen = \(\frac{9}{{18}} \times 1 = 0.5\;g \approx 1\)

Therefore the unknown hydrocarbons contains 24 g of carbon and 1 g of hydrogen.