J OURNAL #5 Calculate the percentage composition of silver (I) sulfate

T ODAY WE WILL DETERMINE AN EMPIRICAL FORMULA FROM EITHER A PERCENTAGE OF A MASS COMPOSITION.

E MPIRICAL FORMULA When a new substance is synthesized, it is analyzed to find its percentage composition. From this data, the empirical formula can be determined. An empirical formula consists of the symbols for the elements combined in a compound, with subscripts showing the smallest whole-number ratio of the different atoms in the compound.

C ALCULATING THE E MPIRICAL FORMULA To determine a compounds empirical formula from its percentage composition: 1. Convert percentage composition to a mass composition 2. Assume that you have a 100g sample 3. Calculate the amount of each element in the sample 4. Convert the mass to a composition in moles

E XAMPLE : The percentage composition of diborane is 78.1g of B and 21.9% H. 100g of diborane contains 78.1g of B and 21.9g of H 1 mol B g B 1 mol H 1.01 g H 78.1 g B x = 7.22 mol B 21.9 g H x = 21.7 mol H

E XAMPLE These values give a mole ratio of 7.22 mol B to 21.7 mole H. This is not a ratio of smallest whole numbers. To find such a ratio, divide each number of moles by the smallest number of existing ratios mol B 21.7 mol H 7.22 The compounds empirical formula is BH 3 = 1 mol B: 3.01 mol H :

P RACTICE : Quantitative analysis shows that a compound contains 32.38% sodium, 22.65% sulfur, and 44.99% oxygen. Find the empirical formula of this compound.

P RACTICE : Analysis of a g sample of a compound known to contain only phosphorus and oxygen indicates the phosphorus content of 4.433g. What is the empirical formula of this compound?