One atom of carbon, two of oxygen.
Percent composition can be used to calculate the percentage of an element/compound in a mixture. From the percent composition, you can also find the empirical formula. And from the empirical formula you can find the actual molecular weight.
If it tells you to find the empirical formula when percent composition is given or if the mass of each element is given in a specific compound.
Not completely. The empirical formula of a substance can be determined from its percent composition, but a determination of molecular weight is needed to decide which multiple of the empirical formula represents the molecular formula.
Cr3Si2 is the empirical formula for a compound containing chromium and silicon an has 73.52 mass percent chromium.
The empirical formula is the simplest ratio of the elements within a compound. Therefore, it can be used to calculate the percentage of an element within a compound. For example, the empirical formula for sodium chloride is NaCl. From this, we can see that the ratio of sodium ions to chloride ions is 1Na : 1Cl. Therefore, a sodium chloride molecule is composed of 50% sodium and 50% chloride.
Because unlike the empirical formula, the molecular formula does not have to be the simplest ratio.If by chance you are given the percent composition of the elements in a substance, you could calculate the empirical formula and then the empirical formula's mass. However, the molecular formula equation is molecular formula= (empirical formula)n, where n is the mass of the molecular formula divided by the mass of the empirical formula. You would, therefore, need to know the mass belonging to the molecular formula, which you are not given.
Based on % composition, one can determine the moles of each element in, say, 100 grams of compound. Then, one can see the mole ratio of all the elements in the compound, and adjust them so as to obtain whole numbers in the lowest possible ratio. This is then the empirical formula.