Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
THE MOLE - EMPIRICAL FORMULA The ____________________________________ of elements in a compound is called the _________________________________. In contrast, the ________________________________ of a compound is the _______________ ____________________________ of each element in the compound. It can be calculated from the mole ratio or from percent composition data. Mole Ratio Example: What is the empirical formula for a compound if a 2.50 g sample contains 0.900 g of calcium and 1.60 g of chlorine? Step One: Determine the number of __________ of Ca and Cl. (You must first determine the atomic mass of each.) Ca 0.900g Ca 1 mole Ca = 0.0225 mol 40.08g Ca Cl 1.60g Cl 1 mole Cl = 0.0451 mol 35.45g Cl Step Two: Obtain the ________________________________ for the set of moles. Divide both numbers of moles by the smaller number of moles. The smallest is ___________ mol. Ca 0.0225 mol = 1.00 0.0225 mol Cl 0.0451 mol = 2.004 = 2.00 0.0225 mol Step Three: Look at the ___________ of the two numbers. Round off to whole numbers (there are exceptions to this). Ca Cl 1.00 2.01 becomes becomes Ca Cl 1.00 2.00 The empirical formula is ____________. PRACTICE: Find the empirical formula of the compound with 63.0g Rb and 5.90g O. Percent Composition Example: Sometimes you are given percentages, not masses, and asked to determine the empirical formula. If this is the case, you can change the percentages directly to _______________ because you assume a 100 g sample (100%) Step One: C H O 40.0 g C 1 mole C = __________ mol C 12.01g C 6.71 g H 1 mole H = __________ mol H 1.01g H 53.3 g O 1 mole O = __________ mol O 16.00g O Step Two: To obtain the smallest ratio, divide both numbers of moles by the smaller number of moles (3.33 mol). C 3.33 mol =________ H 6.64 mol = _________ O 3.33 mol = _________ 3.33 mol 3.33 mol 3.33 mol Step Three: Look at the ratio of the two numbers. Round off to whole numbers. C 1.00 becomes C ____ H 1.99 becomes H ____ O 1.00 becomes O ____ The empirical formula is PRACTICE: A. What is the empirical formula for a compound that has 32.8% Cr and 67.2% Cl? What happens when the mole ratios are not whole numbers? B. What is the empirical formula of a compound that contains 53.73% Fe and 46.27% S? RULES TO FOLLOW: - If the ratio is: X.1 or X.9, round up or down. - If the ratio is X.2 to X.8, determine what to multiply it by to get a whole number. - Examples: X.3 x 3 = X.9 which can be rounded X.5 x 2 = X.0 which is a whole number X.4 x 5 = X.0 which is a whole number