(b) An elemental analysis of the acid indicates that it is composed of 5.89% H, 70.6% C, and 23.5% O by mass. What is its molecular formula?
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Step 1: Assume that you have 100 g of the compound. This means that you have 5.89 g of Hydrogen (H), 70.6 g of Carbon (C), and 23.5 g of Oxygen (O).
Step 2: Convert these masses into moles using the molar mass of each element. The molar mass of H is approximately 1 g/mol, the molar mass of C is approximately 12 g/mol, and the molar mass of O is approximately 16 g/mol.
Step 3: Divide each mole value by the smallest number of moles calculated. This will give you the mole ratio of H, C, and O in the compound.
Step 4: If the mole ratios are not whole numbers, multiply them by the smallest number that will convert them all to whole numbers. This will give you the empirical formula of the compound.
Step 5: To find the molecular formula, you need to know the molar mass of the compound. Divide the molar mass of the compound by the molar mass of the empirical formula. This will give you a whole number, which you multiply by the subscripts in the empirical formula to get the molecular formula.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Empirical Formula
The empirical formula represents the simplest whole-number ratio of the elements in a compound. To determine the empirical formula from percentage composition, one converts the percentages to moles by dividing by the atomic masses of the elements. This ratio helps in identifying the basic composition of the compound before determining the molecular formula.
The molecular formula indicates the actual number of atoms of each element in a molecule of a compound. It can be derived from the empirical formula by multiplying it by a whole number, which is determined by comparing the molar mass of the compound to the molar mass of the empirical formula. This formula provides more specific information about the compound's structure.
Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). To find the molecular formula, one must first calculate the molar mass of the compound using the atomic masses of its constituent elements. This value is essential for determining the relationship between the empirical and molecular formulas.
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