What is the molecular formula of glycerol (a compound containing C, H, and O) from the following
combustion analysis: when 2.00 g glycerol are combusted, 2.865 g CO2 and 1.564 g H2O are recovered.
I already found uts molar mass its 92g/mol
To find the molecular formula of glycerol, we need to determine the ratio of carbon, hydrogen, and oxygen atoms present in the compound.
Step 1: Find the moles of each product:
In the combustion analysis, 2.865 g of CO2 and 1.564 g of H2O are recovered. To convert these masses to moles, we need to divide them by their respective molar masses.
The molar mass of CO2 is 44 g/mol, so the moles of CO2 recovered is 2.865 g / 44 g/mol = 0.0651 mol.
The molar mass of H2O is 18 g/mol, so the moles of H2O recovered is 1.564 g / 18 g/mol = 0.087 mol.
Step 2: Determine the moles of carbon and hydrogen in the compound:
Since CO2 contains one carbon atom and H2O contains two hydrogen atoms, the number of moles of carbon and hydrogen in the compound can be calculated as follows:
Carbon atoms: 0.0651 mol of CO2 x 1 mol of C/1 mol of CO2 = 0.0651 mol of C
Hydrogen atoms: 0.087 mol of H2O x 2 mol of H/1 mol of H2O = 0.174 mol of H
Step 3: Calculate the moles of oxygen in the compound:
To find the moles of oxygen, subtract the moles of carbon and hydrogen from the total moles of the compound:
Total moles of compound: 2.00 g / 92 g/mol = 0.0217 mol
Oxygen atoms: Total moles - (moles of carbon + moles of hydrogen)
= 0.0217 mol - (0.0651 mol + 0.174 mol) = -0.2174 mol
The negative value for moles of oxygen indicates an error in the calculations, as the number of oxygen atoms cannot be negative. Therefore, we need to adjust our assumption that there is one oxygen atom in the compound.
Step 4: Determine the empirical formula:
To find the empirical formula, divide the number of moles of each element by the smallest number of moles to obtain the simplest whole number ratio.
Carbon: 0.0651 mol / 0.0217 mol = 3
Hydrogen: 0.174 mol / 0.0217 mol = 8
Oxygen: 0.2174 mol / 0.0217 mol = 10
The empirical formula of glycerol is C3H8O10.
Step 5: Find the molecular formula:
Finally, to find the molecular formula, divide the molar mass of the compound (92 g/mol) by the molar mass of the empirical formula (the sum of the atomic masses of the atoms in the empirical formula).
Molar mass of empirical formula: (3*12.01) + (8*1.01) + (10*16.00) = 104.19 g/mol
Molecular formula: 92 g/mol / 104.19 g/mol = 0.884
We round this value to the nearest whole number, giving us a molecular formula of C3H8O10.