LeChatelier's Principle Mini Lab
Hiba Al-Ramahi, Mirela Dedic, Joey Fritsche, Brett Schlereth
Collect two beakers. Obtain about 10 mL of fresh seltzer water and pour it in one of the beakers. Add about 20 drops of 0.04% Bromcresol Green Indicator to the water beaker. Mix the solution, and set to the side. Then, repeat the action of adding the same amount of water and Bromcresol Green Indicator in a beaker with one another. Mix the solution, and then draw up about 10 mL of the seltzer/indicator solution into a 30 mL syringe. Seal the syringe by pushing a tip cap firmly onto its open end. Decrease the pressure by pulling the syringe up. Release the solution into the beaker. Note the changes in color.
Change In Pressure:
Shifts to the left because decreased pressure shifts to the most amount of gas moles which is the reactant side. There are no gases in the products versus 2 gas moles in the reactant side. pH should then go up. This is shown by the Bromcresol Green Color Chart which indicated the pH of the color change.
Initially, the solution is green which the pH is 4.2 based on the Bromcresol Green Color Chart. When the pressure was decreased in the syringe, the solution turned into a bluish green with a 4.6 pH.
Solution of Fresh Seltzer Water and Bromcresol Green Indicator.
Decreased Pressure Solution
Solution in the beaker from a syringe where the pressure was decreased.
Bromcresol Green Color Chart
Mg(OH)2 ↔ Mg^+2 +2OH^-1
OH^-1 + H^+1 ↔ H2O
Obtain about 10 mL of the Milk of Magnesia Solution and add this to a 250 mL beaker. Then, add approximately 50 mL of distilled water along with 10 drops of the Universal Indicator Solution. Put the stirring rod in the beaker. Place the beaker on the stirring plate, and turn it on the lower level to mix the solution. Note the present color of the solution. Add 10 mL of Hydrochloric Acid to the stirring solution. Note the color change. Then, add 10 mL of the Milk of Magnesia Solution to the stirring solution. Note the color change.
Change In Concentration:
Shifts to the right when the Hydrochloric Acid is added. It adds more Hydrogen ions which is the product side. Water is created within the solution which is why the glimpse of the color green is shown in the solution. Green is a neutral pH (7.0) so that means water is present. The color pink is from the presence of hydrogen ions from the acid and has a low pH. The color blue is from the excess of the Magnesia Solution. This is shown through the pH scale which indicated the pH of the color change.
Initially, the solution was lavender which had about a pH of 10. After 10 mL of Hydrochloric acid was added to the stirring solution, the color changed to pink with a pH of about 4.5, then to an orange color with a pH of about 5 to a seafoam green with a pH of about 7.5, and lastly to a dirty blue with a pH of about 8.5. When the milk of magnesia was added again, the solution returned to its original color in the closest manner.