Disruption of Equilibrium (Salvador Garcia)

Title: The title should be descriptive so others will know what it is about.

Principle(s) Investigated: Oxidation and Reduction reactions, equilibrium, Le Chatelier’s Principle

Standards :HS-PS1-5, HS-PS1-6.

Materials: Flask, potassium hydroxide (KOH), methylene blue, glucose

Procedure: Add 8 grams of KOH to 300mL of water in a 500mL erlenmeyer flask. Then add 10 grams of glucose to KOH solution. Use a dropper to add 2-3 drops of methylene blue indicator solution then stopper flask to swirl the solution. After standing the solution should turn colorless. If no color change occurs add KOH and glucose.

Student prior knowledge: The students must know how to calculate rates of the reactions and how they are affected by concentration and temperature. Students must be aware of concept of equilibrium as a state where forward rate of reaction is the same as reverse rate of reaction. Students must also be aware of LeChatetier’s principle that describes how reaction will react to changes in order to achieve a state of equilibrium. Students must also understand oxidation and reduction reactions.

Explanation: Methylene blue indicator is reduced in the flask by ionized glucose causing it to be colorless. The glucose becomes ionized by the basic conditions caused by KOH. Methylene blue indicator is exposed to O₂ and oxidized but the rate of reduction is greater. When the solution is shaken it increases the O₂ that is available to the solution increasing the rate of oxidizing reaction due to increasing reactants explained by LeChatetier’s principle. The oxidized methylene present is seen by the blue color of solution. Due to the increased concentration of oxidized methylene blue the rate of reaction to favor the reduction, dissipating the blue color in solution. If the stopper is not removed after flask is shaken then the oxygen in the flask would consumed and not replenished. The smaller amount of oxygen cause less amount of change to the point that reaction could not be observed after a certain amount of shaking. Opening the flask replenishes the oxygen in flask equilibrating it with the oxygen in the atmosphere. Oxygen acts as the oxidation agent oxidizing methylene blue and methylene blue acts as a reducing agent reducing glucose.

Questions & Answers:1. Beside oxygen as a limiting reactant what other substance can limit the reactions?

Ionized glucose is another reactant that is not replenished in the reaction and can completely oxidize.

2. What are some other independent factors that can be altered in the experiment that would affect the rates?

Temperature is can be used as an independent variable, changes in rates of reactions can be observed in colder or warmer temperatures. Temperatures would also change equilibrium constants.

3. What color of solution would be favored is kept still with oxygen being bubbled in.

If supply of oxygen is present the reaction would favor the solution becoming blue thus the oxidation of methylene blue, the reduction reaction would also be occurring causing the solution to be a lighter blue.

Applications to Everyday Life: Indicators are used various jobs using equilibrium of oxidation and reduction reactions. They use equilibrium of reactions, if certain concentrations are high it drives reactions that can be seen visibly like pH indicators used in pools. Acids and bases dissociate based equilibrium making them good buffers.

Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.

Videos: Include links to videos posted on the web that relate to your activity. These can be videos you have made or ones others have made.