Complete combustion of 7.00 g of a hydrocarbon produced 21.4 g of CO2 and 10.2 g of H2O. What is the empirical formula for the hydrocarbon?
Convert 21.4g CO2 to g C and subtract that number from 7.00 g to find g H.
mols C = g/atomic mass
mols H = g/atomic mass
Then find the ratio of the elements to each other. Post your work if you get stuck.
To determine the empirical formula for the hydrocarbon, we need to find the mole ratio between the elements present in the compound.
1. Start by calculating the number of moles of each component: CO2 and H2O.
- Moles of CO2: molar mass of CO2 = 12.01 g/mol (C) + 2(16.00 g/mol) (O) = 44.01 g/mol
- Moles of CO2 = 21.4 g CO2 / 44.01 g/mol CO2 = 0.487 mol CO2
- Moles of H2O: molar mass of H2O = 2(1.01 g/mol) (H) + 16.00 g/mol (O) = 18.02 g/mol
- Moles of H2O = 10.2 g H2O / 18.02 g/mol H2O = 0.566 mol H2O
2. Use the coefficients of the balanced chemical equation to find the mole ratio between carbon, hydrogen, and oxygen in the compound. In complete combustion reactions, hydrocarbons react with oxygen to produce carbon dioxide and water. The balanced equation for the reaction is:
CxHy + O2 -> CO2 + H2O
From the balanced equation, we can see that the mole ratio between carbon and CO2 is 1:1, and between hydrogen and H2O is 2:1.
3. Calculate the number of moles of carbon and hydrogen in the hydrocarbon:
- Moles of carbon = 0.487 mol CO2 * 1 mol C / 1 mol CO2 = 0.487 mol C
- Moles of hydrogen = 0.566 mol H2O * (2 mol H / 1 mol H2O) = 1.132 mol H
4. Divide the mole values by the smallest of the two mole values to obtain the simplest whole-number ratio:
- C: 0.487 mol / 0.487 mol = 1
- H: 1.132 mol / 0.487 mol = 2.32
5. Round the values to the nearest whole number:
- C: 1
- H: 2
6. The empirical formula of the hydrocarbon is CH2.
Therefore, the empirical formula for the hydrocarbon is CH2.