Chemical Equilibrium
Chemical Equilibrium: Le Chatelier Principle
By
Sarah Ramos and Kristina Todorovic
Chemistry 203 DEN
Dr. Mohamed El-Maazawi
Part A. Acid-Base Indicators
Purpose
In this part of the experiment, we will find a reagent that will shift the acid-base equilibrium reaction described by Equation (2) in one direction and then a second reagent that will cause the equilibrium position to shift back in the opposite direction.
Introduction
An acid–base indicator is a substance that changes color as the pH of a solution changes. Consistent with LeChâtlier’s principle, if a solution containing the indicator becomes acidic (e.g., with the addition of H+), the equilibrium will shift to the left, and the solution will become yellow. On the other hand, if the solution becomes basic (e.g., if OH– ions are added, which would reduce the [H+]), the equilibrium will shift to the right and the solution will become purple. At intermediate pH values there will be a mixture of both HB and B–, and the solution will take on a green color. Some indicators exhibit only two colors and some exhibit a wide range. Each indicator must be individually studied to determine its behavior as a function of pH. Le Chatelier 's Principle states that if an equilibrium system is subjected to a stress, the system will react to remove the stress by either: forming more products using up reactants, or reverse the reaction and forming more reactants, using up products. In this experiment several equilibrium systems will be formed. By putting different stresses on the systems, we will observe how equilibrium systems react to a stress. Acid-base indicators are large organic molecules that can gain and lose hydrogen ions to form substances that have different colors. It is the color of the ion that will indicate how the equilibrium system is being affected.
Procedure
Approximately 5 mL of deionized water was added to a test tube and a few drops of the methyl
By
Sarah Ramos and Kristina Todorovic
Chemistry 203 DEN
Dr. Mohamed El-Maazawi
Part A. Acid-Base Indicators
Purpose
In this part of the experiment, we will find a reagent that will shift the acid-base equilibrium reaction described by Equation (2) in one direction and then a second reagent that will cause the equilibrium position to shift back in the opposite direction.
Introduction
An acid–base indicator is a substance that changes color as the pH of a solution changes. Consistent with LeChâtlier’s principle, if a solution containing the indicator becomes acidic (e.g., with the addition of H+), the equilibrium will shift to the left, and the solution will become yellow. On the other hand, if the solution becomes basic (e.g., if OH– ions are added, which would reduce the [H+]), the equilibrium will shift to the right and the solution will become purple. At intermediate pH values there will be a mixture of both HB and B–, and the solution will take on a green color. Some indicators exhibit only two colors and some exhibit a wide range. Each indicator must be individually studied to determine its behavior as a function of pH. Le Chatelier 's Principle states that if an equilibrium system is subjected to a stress, the system will react to remove the stress by either: forming more products using up reactants, or reverse the reaction and forming more reactants, using up products. In this experiment several equilibrium systems will be formed. By putting different stresses on the systems, we will observe how equilibrium systems react to a stress. Acid-base indicators are large organic molecules that can gain and lose hydrogen ions to form substances that have different colors. It is the color of the ion that will indicate how the equilibrium system is being affected.
Procedure
Approximately 5 mL of deionized water was added to a test tube and a few drops of the methyl
References: Petrucci, R.H., Herring, F.R., Madura, J.D, Bissonnette, C. 2010. General Chemistry: Principles and Modern Applications. Prentice Hall. Hardcover