Examples: Determining Empirical & Molecular Formulas of Compounds - P2O5 & Hydrazine, Exams of Chemistry

Download Examples: Determining Empirical & Molecular Formulas of Compounds - P2O5 & Hydrazine and more Exams Chemistry in PDF only on Docsity! PRACTICE PROBLEMS: 1. The empirical formula for a common drying agent is P2O5. The molecule has a molar mass of 283.88 g/mol. Find the molecular formula of the compound. Answers: - When determining Molecular Formulas, you must first determine the Empirical formula. In this problem, the Empirical formula is given. - Since you are given the Empirical formula, we can determine the Molecular formula by using the following equation: )( )( calculatemustyoumassFormulaEmpirical problemtheingivenmassFormulaMolecular n - Therefore, we must first determine the Empirical formula mass for P2O5 : P2O5 = ( 2 ) ( 30.97 g / mol ) + ( 5 ) ( 16.00 g/mol ) = 141.94 g / mol - Let’s now insert the values into the equation and solve for “n”: 2 94.141 88.283 mol g mol g massFormulaEmpirical massFormulaMolecular n - I guess now would be a good time to discuss the significance of “n”… “n” represents the multiplier that we must use to determine the molecular formula. Recall, Empirical formula represents the “smallest-whole-number ratio” of elements within a compound. Molecular formula represents the “actual” number of elements within a compound (that is not an ionic compound – therefore, molecular (hence the name)). So… ( P2O5 )n ; where n = 2 ( P2O5 )2 = P4O10 - Since we calculated “n” to equal 2, then the Empirical formula is multiplied by a factor of two to determine the molecular formula for the compound. Empirical Formula = smallest whole number ratio Molecular Formula = the actual formula for the compound Yes, in some cases - the compounds have the same formula for empirical and molecular…