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
Empirical Formula Recall: Chemical Formula – Relative number of various types of atoms present in a compound Suppose a compound ‘A’ contains C, H, and O. We analyze 0.2015g of compound ‘A’ and find it contains 0.0806g of C, 0.01353g of H and 0.1074g of O. How can we determine its chemical formula? MASS → MOLES! 1 1 mol C C = 0.0806 × = 0.00671 mol C 12.01 g C 1 mol H H = 0.01353 g × 1.008 g H = 0.01342 mol H 1 mol O O = 0.1074 g O × = 0.00671 mol O 16.00 g O What do these results tell us about the chemical formula? 1. The compound contains the same number of C and O atoms 2. There are twice as many H atoms as C atoms and O atoms The relative number of C,H, and O atoms is expressed by the formula CH2O The formula that expresses the smallest whole number ratio of atoms present in a compound is called the empirical formula (simplest formula). The actual formula is called the molecular formula. 2 How to calculate the empirical formula from the mass An oxide of aluminum is formed by the reaction of 4.151g of aluminum with 3.692g of oxygen. What is the empirical formula? 1. Determine the mass of each element 2. Determine the number of moles of each type of atom 1 mol Al 4.151g Al × = 0.1539 mol Al atoms 26.98 g Al 1 mol O 3.692 g O × = 0.2308 mol O atoms 16.00 g O Because chemical formulas use whole numbers, next find the integer ratio of atoms 3 3. Divide the number of moles of each element by the smallest number of moles 0.1539 mol Al = 1.000 mol Al atoms 0.1539 0.2308 mol O = 1.500 mol O atoms 0.1539 We now know the compound contains 1.500 moles of O and 1.000 moles of Al. We could leave it like this but atoms are whole in compounds! So…. 4. If the numbers are not integers, multiply by the smallest integer that will convert all of the numbers to whole numbers. These numbers are the empirical formula 1.500 mol O × 2 = 3 mol O atoms 1.000 mol Al × 2 = 2 mol Al atoms The empirical formula = Al2O3 4 Determining the Molecular Formula • Obtain the empirical formula • Calculate the mass corresponding to the empirical formula • Calculate the ratio molar mass empirical formula mass • The integer from the previous step represents the number of empirical formula units in one molecule. When the empirical formula subscripts are multiplied by this integer, the molecular formula results. This procedure is summarized by the equation: molar mass molecular formula = ( empirical formula ) × empirical formula mass 5