1. Molecular Formula

2. Compare mass of empirical formula to formula mass of molecule X (empirical formula) = (molecular formula)‏

3. Sample Problem 7-14 We found the empirical formula for a compound of phosphorous and oxygen to be P 2 O 5. Experimentation shows that the molar mass of this compound is 283.89 g/mole. What is the compound's molecular formula? Find mass of empirical formula:  2P: 2 (30.9738) = 61.9476  5O: 5(15.9994) = 79.997  Sum: 141.9446 g/mole

4. Sample Problem 7-14 Continued Compare molar mass to empirical mass:  283.89/141.9446 = 2 Write molecular formula:  P 2 O 5 x 2 = P 4 O 10