Final answer:
To determine the percent composition and empirical formula of a herbicide, one analyses a 100 g sample to obtain grams and convert those to moles for each element. The smallest mole ratio is used to determine the empirical formula. For the molecular formula, the compound's molar mass divided by the empirical formula mass yields a multiplier for the empirical formula.
Step-by-step explanation:
Percent Composition and Empirical Formula of a Herbicide
To determine the percent composition of a herbicide, one must start by assuming a 100 g sample of the compound, which allows us to directly convert given percentages into grams. Each element’s mass in grams is then converted to moles using its molar mass. The mole ratio of each element obtained is essential for determining the empirical formula. The empirical formula represents the simplest whole-number ratio of elements in the compound.
To obtain the molecular formula from the empirical formula, the empirical formula mass (EFM) is calculated first. The molecular formula is then determined by dividing the molar mass of the compound by the EFM. The result should be a whole number, which, when multiplied by the empirical formula, gives the molecular formula.
For example, if a compound contains carbon, hydrogen, and oxygen, we determine the ratio of these in the simplest whole numbers to find the empirical formula. If we desire the molecular formula, we must also know the molecular weight for precise determination.
Note that the empirical formula and molecular formula can sometimes be the same if the compound exists as its simplest units. However, a molecular formula contains a multiple of the empirical formula representing actual numbers of atoms within a molecule of the compound.