Equilibrium Lab, or

LeChatlier’s Really Stressing Me Out

Purpose: To examine some reversible reactions; to examine reactions at equilibrium.

To examine some of the stresses that affect reversible reactions and dynamic equilibriums.

Methods: This is a lab in four parts:

PART 1: Magical Blue Flask

  1. In a small earlenmeyer flask, obtain equal volumes of 0.13 M Dextrose and 1 M NaOH solutions, approx. 15 mL of each.
  2. Add 3 drops of Methylene Blue.
  3. Shake vigorously.
  4. Rest the flask on your table and observe until you see a change.
  5. Repeat steps 3 and 4.
  6. Split the solution into 4 test tubes, labeled A-D.
  7. In A, add 5 ml NaOH.
  8. In B, add 5 ml Dextrose
  9. Place C in a hot water bath—NOT boiling.
  10. Place D in an ice bath.
  11. Shake each tube again, noting:
  12. Which one underwent the color change the fastest.
  13. Which one underwent the color change the slowest.

PART 2: Cobalt Blue? Pink? Blue? Pink?

  1. Obtain 1 ml Co(NO3)2 in a small test tube. Note the color CLOSELY.
  2. See Mr. Remenap for the addition of Conc. HCl. Note the color closely.
  3. Place this solution in an ice bath for 5 min., or until a change is noted.
  4. Place the solution in boiling water for 5 min, or until a change is noted.
  5. Split the sample into 2 small tubes labeled E-F.

a. In E, add 3 more drops of Co(NO3)2.

b. In F, have Mr. Remenap add more HCL.

6. Place both tubes in an ice bath for 3 minutes.

7. Place both tubes in boiling water for 3 minutes.

a. Which tube changed to pink faster?

b. Which tube changed to blue faster?

PART 3: Oranges or Apples?

  1. Obtain 10 ml of BOTH NaOH and HCl in separate test tubes.
  2. Place about 5 ml of NaOH in a test tube, and add 2 drops of Methyl Orange. Note the color.
  3. Add HCl drop-by-drop until a complete change is noted.
  4. Split this sample into two tubes, labeled G-H.
  5. To G, add 2 mL NaOH; note changes.
  6. To H, add 2 mL HCl; note changes.
  7. Add HCl drop by drop to G until it returns to pink.
  8. Add NaOH drop by drop to H until it turns orange.
  9. Place both tubes in an ice bath. Note any changes.
  10. Place both tubes in a hot water bath. Note any changes.

PART 4: I Can See Clearly Now

  1. Obtain 15-20 ml of Ca(OH)2 solution in a small beaker.
  2. Obtain 10-15 ml of both NaOH and HCl in separate test tubes.
  3. Place 10 ml Ca(OH)2 into a test tube.
  4. Add HCl until a change is complete. Note this change.
  5. Add NaOH until a change is noted.

Questions to Ponder:

  1. What you witnessed in this lab were 4 different chemical reactions at their EQUILIBRIUM points. Describe each reaction at its equilibrium point (that is, the point at which the reaction seemed to stop).
  2. Once your reactions reached an equilibrium point, you created a “stress” on the system. Identify the stress in each system, and tell what changes you observed in the reaction.
  3. Make a table showing the reaction names (from above), so that you can read the table and clearly show all of the observations, both at equilibrium and after the stress was added; leave a space for what happens after the stress is “removed.”
  4. Once the stresses were removed, could you stress the reaction in another manner? For instance, were you able to change the Ca(OH)2 cloudy by heating it or cooling it? Or were you able to change the clear/blue solution through the addition of other chemicals?
  5. Attempt to write balanced chemical equations for reactions for reactions 2 and 4, without stress, and 3 with the stress. <Don’t even bother with #1—it’s FAR more complex than the other three reactions>
  6. What characteristic of Methyl Orange made it change color in the acid solution and the base solution? Do you know a general name for chemicals that undergo such a transformation?
  7. What characteristic of Calcium Hydroxide allowed us to distinguish it from the clear solution of water, HCl, and the Calcium Hydroxide? Think about what products were being made, and what was therefore being made when you added NaOH.

Questions to Ponder:

  1. What you witnessed in this lab were 4 different chemical reactions at their EQUILIBRIUM points. Describe each reaction at its equilibrium point (that is, the point at which the reaction seemed to stop).
  2. Once your reactions reached an equilibrium point, you created a “stress” on the system. Identify the stress in each system, and tell what changes you observed in the reaction.
  3. Make a table showing the reaction names (from above), so that you can read the table and clearly show all of the observations, both at equilibrium and after the stress was added; leave a space for what happens after the stress is “removed.”
  4. Once the stresses were removed, could you stress the reaction in another manner? For instance, were you able to change the Ca(OH)2 cloudy by heating it or cooling it? Or were you able to change the clear/blue solution through the addition of other chemicals?
  5. Attempt to write balanced chemical equations for reactions for reactions 2 and 4, without stress, and 3 with the stress. <Don’t even bother with #1—it’s FAR more complex than the other three reactions>
  6. What characteristic of Methyl Orange made it change color in the acid solution and the base solution? Do you know a general name for chemicals that undergo such a transformation?
  7. What characteristic of Calcium Hydroxide allowed us to distinguish it from the clear solution of water, HCl, and the Calcium Hydroxide? Think about what products were being made, and what was therefore being made when you added NaOH.