Empirical vs. Molecular Formula Our experience with chemicals involves the use of molecular formulae. This formula communicates the number of atoms of each kind of element present in 1 molecule of compound. The empirical formula can be thought of as a reduced version of the molecular formula. The empirical (simplest) formula indicates the lowest whole number ratio of the elements in a compound. * Copy table 6.1 on page 207 in your notes using the same title for your chart. Problems: a) P2O4 b) C4H10 c) N2 O4 d) N2O5 Write the empirical formula for each of the following: Example 1: Determine the empirical formula of a compound composed of 70.1% silver, 9.1% nitrogen, and 20.8% oxygen. Solution: Element Let there be 100.0 g of the compound. Mass (g) Molar Mass (g/mol) Amount (mol) Ratio silver 70.1 107.9 0.65 1 nitrogen 9.1 14.0 0.65 1 oxygen 20.8 16.0 1.30 2 Therefore the empirical formula is AgNO2. Example 2: A sample of matter consists of 29.1% Na, 40.5% S, and 30.4% O. Determine the empirical formula of this compound. Solution: Let there be 100.0 g of the compound. Element Mass (g) Molar Mass (g/mol) Amount (mol) sodium 29.1 23.0 1.27 1 2 sulphur 40.5 32.1 1.26 1 2 oxygen 30.4 16.0 1.90 1.5 3 Therefore the empirical formula is Na2S2O3. Homework 1. Read pages 207 - 214 2. P. 209 # 9-12 3. P. 211 # 13-16 Ratio