In chemistry, the empirical formula of a chemical compound is a simple expression of the relative number of each type of atom in it.
In contrast, the molecular formula identifies a multiple of the smallest whole number ratio in moles.
For example, n-hexane, a chemical compound has the molecular formula CH3CH2CH2CH2CH2CH3, implying that it has a straight chain structure, 6 carbon atoms, and 14 hydrogen atoms. Hexane's molecular formula is C6H14, and its empirical formula would be C3H7 showing a C:H ratio of 3:7.
1. Start with the number of grams of each element, given in the problem.
If percentages are given, assume that the total mass is 100 grams so that
the mass of each element = the percent given.
2. Convert the mass of each element to moles using the molar mass from the periodic table.
n = m / M
n = moles
m = mass (g)
M = molar mass (gmol^-1)
3. Divide each mole value by the smallest number of moles calculated.
4. Round to the nearest whole number. This is the mole ratio of the elements and is
represented by subscripts in the empirical formula.
If the number is too far to round (x.1 ~ x.9), then multiply each solution by the same
factor to get the lowest whole number multiple.
e.g. If one solution is 1.5, then multiply each solution in the problem by 2 to get 3.
e.g. If one solution is 1.25, then multiply each solution in the problem by 4 to get 5.
Once the empirical formula is found, the molecular formula for a compound can be determined if the molar mass of the compound is known. Simply calculate the mass of the empirical formula and divide the molar mass of the compound by the mass of the empirical formula to find the ratio between the molecular formula and the empirical formula. Multiply all the atoms (subscripts) by this ratio to find the molecular formula.
hope this hepls:-D
· 1 decade ago