Lab 1: Determining the Empirical Formula of a Compound
Purpose: The purpose of this lab is to determine the empirical formula of a compound. In order to do this, the empirical formula, which is the simplest whole number ratio of elements in a compound is found by looking at the stoichiometric ratio of atoms in a specific compound.
Question: What is the stoichiometric composition of an ionic compound?
The empirical formula of a compound is the simplest whole number ratio of the elements in the compound. The stoichiometric ratio of the different types of atoms in a compound is given by that ratio of whole numbers. One mole of a substance has the number of moles of different types of atoms in the same ratio as the stoichiometic ratio.
For example, the formula reflects a 2:1 stoichiometric ratio between hydrogen and oxygen atoms. Also, one mole of molecules has a 2:1 molar ratio between the total number of hydrogen and oxygen atoms. That is, there are 2 moles of hydrogen and 1 mole of oxygen atoms in 1 mole of molecule.
The empirical formula can be determined experimentally if a compound can be synthesized from its elements. This process requires three steps: determining the mass of each element in the compound; calculating the number of moles of each element in the sample; and expressing the molar ratio of each element as the smallest whole number.
Molecular oxygen is very reactive, whether in pure form or in a mixture such as air. The most abundant component of air, nitrogen, is relatively unreactive. An element reacting with oxygen forms an oxide. For example, magnesium and oxygen form magnesium oxide:
The reaction of nitrogen with an element forms a nitride. Because oxygen has a greater reactivity than nitrogen, the oxide is more likely to form.
In this experiment, you will burn magnesium (Mg) in air to form magnesium oxide and magnesium nitride. The magnesium nitride will be converted to magnesium hydroxide and ammonia by adding water. Upon heating, the magnesium hydroxide will be converted to magnesium oxide with the release of water vapor.