Recrystallization of Benzoic Acid
Abstract
The objective of this experiment was to observe multi-step purification of benzoic acid after performing the extraction from a mixture containing benzoic acid, cellulose, and methyl orange. Recrystallization was done to remove impurities from the sample. The amount of BA recovered during recrystallization is much less than the extracted amount of BA. The difference between the pure and impure samples was observed by comparison of melting points. It was found that impure samples will have a lower and wider melting point range. The experiment performed was important because it provides important knowledge about the chemical nature and reactivity’s of various compounds that can be used in everyday life.
Introduction
Now that the desired compound is extracted, it still contains impurities. These impurities can be removed through a process called recrystallization. Recrystallization is a method for purifying solid compounds which are frequently the products of organic reactions. This theory is based on three important concepts. The first is that a compound is always more soluble in hot solvents than in cold solvents. Secondly, molecules have unique solubility properties. Lastly, a growing crystal will only accept similar entities into its lattice. This is related to the crystal lattice theory which states crystal formation is anti-entropic based on the equation ∆G =∆H-T∆S. There are three stages of solubility: collision, dissociation, and solvation. In order to raise the probability of collision between the solute and solvent, heat is added to the system. When this occurs, the solute will attack the crystalline structure of the solute and start dissociation. As dissociation continues until all the molecules are free, solvation occurs. Choosing the right solvent is important when considering recrystallization. The solute must have a high temperature coefficient in the solvent: it must be soluble at high temperatures and insoluble at low
The objective of this experiment was to observe multi-step purification of benzoic acid after performing the extraction from a mixture containing benzoic acid, cellulose, and methyl orange. Recrystallization was done to remove impurities from the sample. The amount of BA recovered during recrystallization is much less than the extracted amount of BA. The difference between the pure and impure samples was observed by comparison of melting points. It was found that impure samples will have a lower and wider melting point range. The experiment performed was important because it provides important knowledge about the chemical nature and reactivity’s of various compounds that can be used in everyday life.
Introduction
Now that the desired compound is extracted, it still contains impurities. These impurities can be removed through a process called recrystallization. Recrystallization is a method for purifying solid compounds which are frequently the products of organic reactions. This theory is based on three important concepts. The first is that a compound is always more soluble in hot solvents than in cold solvents. Secondly, molecules have unique solubility properties. Lastly, a growing crystal will only accept similar entities into its lattice. This is related to the crystal lattice theory which states crystal formation is anti-entropic based on the equation ∆G =∆H-T∆S. There are three stages of solubility: collision, dissociation, and solvation. In order to raise the probability of collision between the solute and solvent, heat is added to the system. When this occurs, the solute will attack the crystalline structure of the solute and start dissociation. As dissociation continues until all the molecules are free, solvation occurs. Choosing the right solvent is important when considering recrystallization. The solute must have a high temperature coefficient in the solvent: it must be soluble at high temperatures and insoluble at low
Cited: Wikipedia: The Free Encyclopedia. Wikimedia Foundation, Inc. 22 July 2004. Thurs. 7 Oct. 2010. Zubrick, James. The Organic Chem Lab Survival Manual. 6th. Pittsburgh: John Wiley & Son, Inc., 2008. Print.