(P)? CHAPTER 3 The Percentage composition is defined as the percentage by mass of the various elements in a compound. The percentage of an element in a compound is found by using the formula of the compound and the atomic masses of the elements in the compound. It is more correctly called the theoretical percentage composi- tion by mass of the element in that compound. The percentage composition by mass of an element is given by the formula: nx Molar mass of element x100% Molar mass of compound Where n is the number of atoms of the element in the formula of the compound. If the mass of an element and compound is measured experimentally, the per- cent composition by mass of an element is calculated as the following: Mass of element Mass of compound MOLE CONCEPT AND STOICHIOMETRY Percentage Composition by mass of an Element = 489 Example 1: 1) Calculate the percentage composition by mass of nitrogen in ammonium nitrate, NH NO, [Note: N=14, H=1, O=16] Solution: (3x16) = 80g/mol 10/2/161-106g/mol X100% = 45.3% x1