Final answer:
To determine the empirical and molecular formulas of a hydrocarbon from combustion data, calculate the moles of carbon and hydrogen, derive the empirical formula as CH2, and then find that the molecular formula is C2H4, which means the correct answer is option (c) Empirical: CH2, Molecular: C2H4.
Step-by-step explanation:
When 2.996 grams of a hydrocarbon CxHy were burned, 9.401 grams of CO2 and 3.849 grams of H2O were produced. To find the empirical formula and molecular formula, start by calculating the moles of carbon and hydrogen in the products. From the moles of CO2, we can find the moles of carbon, and from the moles of H2O, we find the moles of hydrogen.
The moles of carbon in CO2 are 9.401 grams / 44.01 g/mol = 0.2137 mol, the molar mass of CO2. The moles of hydrogen from H2O are (3.849 grams / 18.02 g/mol) × 2 = 0.4272 mol, as each mole of water has two moles of hydrogen atoms. Therefore, the ratio of carbon to hydrogen in the hydrocarbon is close to 1:2, suggesting an empirical formula of CH2.
To find the molecular formula, compare the empirical formula mass with the molar mass of the compound, which is given as 56.11 g/mol. The mass of the empirical formula CH2 is 12.01 g/mol for carbon plus 2 × 1.01 g/mol for hydrogen, totaling to about 14.03 g/mol. Since the molar mass of the entire molecule is given as 56.11 g/mol, we divide 56.11 g/mol by 14.03 g/mol to find that the molecular formula is essentially four times the empirical formula (approximately 4 × 14.03 ≈ 56.11). Therefore, the empirical formula and the molecular formula of the hydrocarbon are CH2 and C2H4, respectively, which corresponds to option (c) Empirical: CH2, Molecular: C2H4.