A compound has the following composition. C 54.5%, H 9.10% and 0 36.4% its molecular weight is 88.10.
Determine its empirical formula and molecular formula.
Take 100 g sample.
That gives you 54.5 g C, 9.10 g H and 36.4 g O. Now convert those grams to mols.
54.5/12.01 = mols C
9.10/1 = mols H
36.4/16 = mols O.
Determine the ratio of the mols in small whole numbers. To do that, divide the smallest number by itself (thereby assuring you that is 1.00), then divide all of the other mol numbers by that same divisor. That should give you the empirical formula.
The molecular formula is some multiple of the empirical formula. Post your work if you need further assistance.
To determine the empirical formula and molecular formula of the compound, follow these steps:
1. Take a 100g sample of the compound. This means you have 54.5g of carbon (C), 9.10g of hydrogen (H), and 36.4g of oxygen (O).
2. Convert the grams to moles by dividing the mass of each element by its molar mass (atomic weight from the periodic table). Use the equation:
Moles of an element = Mass of the element / Molar mass of the element
For carbon (C): Moles of C = 54.5g / 12.01 g/mol = 4.54 mol
For hydrogen (H): Moles of H = 9.10g / 1.01 g/mol = 9.01 mol
For oxygen (O): Moles of O = 36.4g / 16.00 g/mol = 2.28 mol
3. Determine the ratio of the moles in small whole numbers. Divide each of the moles by the smallest value (in this case, oxygen). This step helps you find the simplest whole number ratio of atoms.
Dividing moles of C by moles of O: 4.54 mol / 2.28 mol = 1.99 (approximately 2)
Dividing moles of H by moles of O: 9.01 mol / 2.28 mol = 3.95 (approximately 4)
Dividing moles of O by moles of O: 2.28 mol / 2.28 mol = 1.00
The ratio of C:H:O is approximately 2:4:1. This means that the empirical formula is C2H4O.
4. Determine the molecular formula by finding the multiple of the empirical formula that matches the molecular weight provided (88.10 g/mol).
Calculate the empirical formula's molar mass:
Molar mass of C2H4O = (2 * molar mass of C) + (4 * molar mass of H) + (1 * molar mass of O)
= (2 * 12.01 g/mol) + (4 * 1.01 g/mol) + (1 * 16.00 g/mol)
= 44.06 g/mol
Divide the molecular weight by the empirical formula's molar mass to find the multiple:
Multiple = Molecular weight / Empirical formula molar mass
= 88.10 g/mol / 44.06 g/mol
= 2
The molecular formula is obtained by multiplying the subscripts of the empirical formula by the multiple:
Molecular formula = (Subscript of C in empirical formula) * Multiple : (Subscript of H in empirical formula) * Multiple : (Subscript of O in empirical formula) * Multiple
= 2 * C2 : 4 * H4 : 1 * O2
= C4H8O2
Therefore, the empirical formula of the compound is C2H4O and the molecular formula is C4H8O2.