An Unknown Compound (M=60.09 g/mol) is composed of Carbon, Hydrogen and Oxygen. Combustion of 0.255 g of the unknown compound produces 0.561 g Carbon Dioxide and 0.306 g of Water. Determine the molecular formula of the compound.
CxHyOz ==> xCO2 + 1/2yH2O
Convert g CO2 and g H2O to g C and g H.
0.561 g CO2 x (atomic mass C/molar mass CO2) = grams C.
0.316 g H2O x (2*atomic mass H/molar mass H2O) = grams H.
0.255 - g C - g H = grams O.
mols C = grams C/atomic mass C = ?
mols H = grams H/atomic mass H = ?
mols O = grams O/atomic mass O = ?
Now find the ratio of the elements to each other the smallest number being 1.00. The easy way to do that is to divide the smallest number by itself then divide the other numbers by the same small number. That will give you x,y,z for the empirical formula. Post your work if you get stuck.
To determine the molecular formula of the compound, we need to find the number of each element present in one molecule of the unknown compound.
Let's start by calculating the number of moles of carbon dioxide (CO2) and water (H2O) produced in the combustion reaction.
1. Calculate the number of moles of CO2:
Mass of CO2 = 0.561 g
Molar mass of CO2 = 44.01 g/mol
Moles of CO2 = Mass of CO2 / Molar mass of CO2
2. Calculate the number of moles of H2O:
Mass of H2O = 0.306 g
Molar mass of H2O = 18.02 g/mol
Moles of H2O = Mass of H2O / Molar mass of H2O
3. Once we have the respective moles of CO2 and H2O, we can determine the ratio of carbon to hydrogen to oxygen atoms in one molecule of the unknown compound.
Let's take the number of moles of CO2 as the limiting reagent, as it is produced in a 1:1 ratio with the unknown compound.
4. Determine the moles of the unknown compound:
Moles of the unknown compound = Moles of CO2
5. Now, let's find the number of moles of carbon in the unknown compound:
Moles of carbon in the unknown compound = Moles of CO2
Since one molecule of CO2 contains one carbon atom, the number of moles of carbon equals the number of moles of CO2.
6. Next, calculate the number of moles of hydrogen in the unknown compound:
Moles of hydrogen in the unknown compound = (Moles of H2O) * (2 moles of hydrogen / 1 mole of water)
Since one molecule of water (H2O) contains two hydrogen atoms, we need to multiply the moles of H2O by 2 to account for the hydrogen atoms.
7. Finally, determine the number of moles of oxygen in the unknown compound:
Moles of oxygen in the unknown compound = (Moles of the unknown compound) - (Moles of carbon) - (Moles of hydrogen)
8. Now that we know the moles of carbon, hydrogen, and oxygen in the unknown compound, we can find their respective ratios. Divide each value by the smallest value among them to normalize the ratios.
9. Using the normalized ratios, we can estimate the empirical formula of the unknown compound. The empirical formula gives the simplest whole-number ratio of atoms in a compound.
For example, if the normalized ratio for carbon is 1, hydrogen is 2, and oxygen is 1, the empirical formula would be C1H2O1, which simplifies to CH2O.
10. Finally, to determine the molecular formula of the unknown compound, we need to know its molecular mass. The molar mass (M) of the unknown compound is given as 60.09 g/mol.
Divide the molecular mass (M) by the empirical formula mass to find the number of empirical formula units in the molecular formula.
Molecular formula = (Molecular mass) / (Empirical formula mass)
By following these steps, you can determine the molecular formula of the unknown compound.