Percent Composition and Empirical Formula of Magnesium Oxide, Lab Reports of Chemistry

Download Percent Composition and Empirical Formula of Magnesium Oxide and more Lab Reports Chemistry in PDF only on Docsity! LAB 4: Percent Composition and Empirical Formula of Magnesium Oxide INTRODUCTION: Percent composition is the mass percent of each element in a compound. It is calculated by dividing the mass of an element in the compound by the total mass of the compound and then multiplying by 100. Mass of the element Percent composition = x 100 Mass of the compound The theoretical percent composition of a compound can be determined using the molecular formula of the compound. Using the periodic table, the atomic mass (amu) for each atom in the compound is determined and added together to find the total mass of the compound. It is called the “theoretical” percent composition because it is assumed the scientific experts who generated the periodic table knew what they were doing. Using the information on the periodic table gives you’re the “expected” or correct answer to the calculation. The experimental percent composition of a compound is determined using experimental data. In this case the mass of the specific elements present in the compound or the mass of the entire compound are known but the molecular formula is unknown. An empirical formula is the simplest whole number ratio of the elements found in a compound. In this lab the empirical formula of magnesium oxide will be determined by reacting magnesium with oxygen in the air. Based on where magnesium and oxygen are located on the periodic table, magnesium will give away 2 valence electrons to become a +2 ion and oxygen will take the 2 valence electrons to become a -2 ion. Since the charges are of equal size, they cancel each other in a 1:1 ratio to form a neutral molecule. According to the periodic table the empirical formula for magnesium oxide should be MgO. The compound magnesium oxide is produced when the element magnesium reacts with oxygen in the air according to the following chemical reaction. 2 Mg + O2 → 2 MgO PURPOSE: The purpose of this lab is to calculate the percent concentration of magnesium oxide and confirm that the empirical formula of magnesium oxide is indeed MgO as predicted from the location of these elements on the periodic table using supplied experimental data. DATA: Mass of empty crucible 11.12 g Mass of crucible with magnesium 11.65 g Mass of crucible and magnesium oxide 12.00 g CALCULATIONS: 1. Show the calculations for determining the mass of magnesium used in the reaction. Mass of magnesium = ___________ g 2. Show the calculations for determining the mass of magnesium oxide produced. Mass of magnesium oxide = __________ g 3. Show the calculations for determining the mass of oxygen in the magnesium oxide. Mass of oxygen = ___________ g 4. Show the calculations for determining the theoretical percent composition of magnesium oxide using the molecular formula MgO and the amu of each element on the periodic table. Theoretical % Mg = ___________ % O = ___________ In some situations the empirical formula of a compound (the smallest whole number ratio of atoms in the compound) is the same as the molecular formula of the compound (the actual number of each type of atom in the compound). In some cases it is not the same and the molecular formula will be some whole number multiple of the empirical formula. To determine the molecular formula of a compound, it is necessary to know the empirical formula and the molecular mass of the compound (usually given in the problem). To determine the correct multiplier to use, divide the molecular mass by the empirical mass. The empirical mass of a compound is calculated by adding the atomic mass (amu) of each atom in the empirical formula. The final step is to multiply each atom in the empirical formula by the multiplier to get the molecular formula. 2. Determine the molecular formulas for the following compounds given the percent composition by mass and the molecular mass. 92.26% C 7.74% H Molecular mass = 78 amu 40.00% C 6.71% H 53.29% O Molecular mass = 60 amu