Empirical Formulas Knowing exactly what it is Percent Composition Breaks down the amount of an element in a compound by percentage
Total mass of element / total mass of compound Result will always be a decimal Multiply by 100 to get the final percentage Practice 1 What is the percent composition of the
elements in NaC2H3O2? Practice 2 What is the percentage of Oxygen in NH4NO3? Practice 3 What is the percentage of Iron in Iron (III)
Carbonate? Empirical formulas Formulas are represented in smallest whole number ratios Derived from percent composition of a
compound Remember 100g = 100 % for easier calculations Talk it Out 1. 2. 3.
4. Change percentage to grams assuming there are 100g of the sample Divide by the molar mass of each element Divide the moles of each element by
the lowest number of moles of all the elements Round to whole numbers to find ratios UNLESS there is .5, then multiply each result by 2 for whole number ratios Problem 1 The percent composition of a compound
was found to be 63.5% Silver, 8.2% Nitrogen, and 28.3% oxygen. Determine the compounds empirical formula. Problem 2 A 170.00g sample of an unidentified compound contains 29.84g of Sodium, 67.49g Chromium, and 72.67g Oxygen.
What is the compounds empirical formula? Problem 3 A 60.00g sample of an tetraethyl lead, a gasoline additive, contains 38.43g of Lead, 17.83g Carbon, and 3.74g Hydrogen. What is the compounds
empirical formula? Molecular Formula You must have the empirical formula first
You must calculate the mass of the empirical formula Dont lose track of your numbers! 1. 2. 3. 4.
5. Calculate empirical formula Calculate the mass of the empirical formula Divide the given mass by the empirical mass, this will give you an element multiplier
Multiply your chemical quantities by the multiplier Rewrite molecular formula with new chemical values Problem 1 Determine the molecular formula of a compound with an empirical formula of
NH2 and a formula mass of 32.06 amu. Problem 2 The empirical formula of a hydrocarbon is found to be CH. Laboratory procedures have found that the molar mass of the compound is 78 g/mol. What is the formula of this compound?
Problem 3 A compound containing 50.05% Sulfur and 49.95% Oxygen has a molar mass of 256.28 g/mol. Determine the empirical and molecular formula of this compound.