Complete combustion of 8.80 g of a hydrocarbon produced 27.1 g of CO2 and 12.5 g of H2O. What is the empirical formula for the hydrocarbon?
Convert mols CO2 to mols C. That's 27.1/44 = ?
Convert mols H2O to mols H. That's 12.5*2/18 = ?
Now find the ratio of C to H with the smaller number being no less than 1.00. The easy way to do that is to divide the smaller number by itself (thereby assuring you of getting 1.00 for that one) and find the empirical formula.
To find the empirical formula of a hydrocarbon, we need to determine the ratio of the elements present in the compound.
1. Begin by converting the given masses of CO2 and H2O into moles. This can be done by using the molar masses of each compound.
The molar mass of CO2:
C: 12.01 g/mol x 1 = 12.01 g/mol
O: 16.00 g/mol x 2 = 32.00 g/mol
Total molar mass of CO2 = 12.01 g/mol + 32.00 g/mol = 44.01 g/mol
The moles of CO2 can be calculated as:
27.1 g / 44.01 g/mol = 0.615 mol
Similarly, calculate the moles of H2O:
H: 1.008 g/mol x 2 = 2.016 g/mol
O: 16.00 g/mol
Total molar mass of H2O = 2.016 g/mol + 16.00 g/mol = 18.02 g/mol
The moles of H2O can be found as:
12.5 g / 18.02 g/mol = 0.693 mol
2. Next, determine the moles of C and H in the hydrocarbon.
From the balanced equation for the combustion of a hydrocarbon, we know that 1 mol of hydrocarbon reacts to produce 1 mol of CO2 and 1 mol of H2O.
Therefore, the number of moles of C and H in the hydrocarbon will be the same as the moles of CO2 and H2O, respectively.
Moles of C = 0.615 mol
Moles of H = 0.693 mol
3. Divide the moles of each element by the smallest value among them to obtain the simplest whole number ratio.
Dividing both moles of C and H by 0.615 (the smallest value), we get:
Moles of C = 0.615 mol / 0.615 mol = 1 mol
Moles of H = 0.693 mol / 0.615 mol = 1.125 mol
Since we want the empirical formula, we need to get whole numbers, so we'll multiply each by 8 to get:
Moles of C = 1 mol x 8 = 8 mol
Moles of H = 1.125 mol x 8 = 9 mol
The simplified whole number ratio is C8H9.
Therefore, the empirical formula for the hydrocarbon is C8H9.