Equilibrium and Reaction Rates.

Equilibrium Lab and Finding K and Rate of Reaction Lab

1. Equilibrium Lab - Le Châtelier's Principle
   1. Introduction/Background: Discuss equilibrium, reversible reactions, Le Châtelier's principle and the factors that affect equilibrium, give examples. The purpose of this lab is to see the effect of a stress on a reaction.
   2. Hypothesis: The reaction to be studied is:
      State and explain the effect of each of the following on the equilibrium of the reaction.
      1. Adding HCl
      2. Adding AgNO_{3 (aq)} (Note: Ag⁺¹ reacts with Cl^-1 to form AgCl_(s))
      3. Adding H₂O
   3. Procedure:
      1. Wear goggles at all times.
      2. Place microplate on white paper.
      3. Add 5 drops CoCl₂ to wells A1-A10, B1-B10, and C1-C10.
      4. Add 1 drop HCl to wells A1, B1, and C1.
      5. Add 2 drops HCl to wells A2, B2, and C2.
      6. Continue in this manner, increasing the drops by one each time, until you have added 10 drops of HCl to A10, B10, and C10.
      7. Record observations.
      8. Part a): Add 1 more drop HCl to each well in row A. Record observations.
      9. Part b): Add 5 drops AgNO₃ to each well in row B. Record observations.
      10. Part c): Add 5 drops H₂O to each well in row C. Record observations.
      11. Carefully rinse out the microplate in the sink. Put materials away.
   4. Data Analysis: Discuss each reaction and its effects on the equilibrium. Refer back to your hypothesis. Explain your observations for each part.
   5. Evaluation and Conclusion as usual, per the lab format handout.
2. Finding K_eq of FeSCN⁺²
   1. Introduction/Background: Discuss K_eq and factors that affect it. Discuss Beer's Law and explain how the concentration of a solution relates to what you see (absorbance). The purpose of this lab is to find the K_eq for the formation of FeSCN⁺². This ion is formed by the reaction:
   2. Write the K_eq expression.
   3. Procedure:
      1. Obtain 5 sample tubes, a light, 2 pipets with a bulb, a sample of each solution, and 3 beakers.
      2. Fill one beaker with distilled water.
      3. Using a pipet, prepare five solutions as follows:
         1. Add 5 mL 0.00200 M SCN^-1 solution to each of 5 sample tubes.
         2. To tube #1, add 5 mL of 0.200 M Fe⁺³ solution. This is your standard tube.
         3. Add 10mL 0.200 M Fe⁺³ solution to a beaker. Add 15 mL water. Pipet 5 mL of this solution into tube #2. Set tube #2 aside.
         4. Pipet 10 mL from the beaker in step 3 into a clean beaker. Add 15 mL water. Pipet 5 mL of this solution into tube #3. Set tube #3 aside.
         5. Rinse out the beaker from step 3 (not the solution just used for tube #3). Pipet 10 mL from the beaker in step 4 into the clean beaker. Add 15 mL water. Pipet 5 mL of this solution into tube #4. Set aside tube #4.
         6. Rinse out the beaker from step 4 (not the solution just used for tube #4). Pipet 10 mL from the beaker in step 5 into the clean beaker. Add 15 mL water. Pipet 5 mL of this solution into tube #5. Set aside tube #5.
         7. All the tubes should be of equal heights. Save the tubes, rinse out the beakers and the pipets.
      4. Place the standard tube (#1) and tube #2 side by side over the light. Use a small pipet to remove some solution from the standard until it appears lighter than tube #2. Gradually add it back to the standard until the two tubes appear the same.
      5. Measure the height of tube #1 and #2. Record.
      6. Repeat steps 4 and 5 using the standard (#1) and tube #3, then tube #4, then tube #5.
   4. Data Table:

      Test Tube #	1	2	3	4	5
      Initial [Fe+3]
      Initial [SCN-1]
      Depth of sample (cm)	----
      Depth of standard (cm)	----
      [FeSCN+2] at equilibrium

   5. Calculations: Show all calculations.
      1. Calculate the initial concentrations of both the SCN^-1 and Fe⁺³. For the SCN^-1, use M₁V₁ = M₂V₂.
         Example: For all tubes: (0.00200 M)(5 mL) = M₂(10 mL total)
         M₂= 0.00100 M = Initial [SCN^-1]
         For [Fe⁺³], use the same equation. However, you will have two calculations after tube #1 because the original solution is diluted in the beaker, then diluted again when added to the tube.
         
      2. Calculate [FeSCN⁺²] for tube #1. Assume the reaction goes to completion using 0.100 M Fe⁺³ and 0.00100M SCN^-1 and the reaction given in the introduction. Calculate the amount of FeSCN⁺² that will form.
      3. Calculate the [FeSCN⁺²] for each tube. Use Beer's law, rearranged to c₁l₁=c₂l₂, where c₁ is the concentration of the standard, l₁ is the depth of the standard, l₂ is the depth of the sample, and c₂ is the equilibrium concentration.
      4. Calculate the K_eq for each tube. Find the equilibrium concentration of Fe⁺³ and SCN^-1 by using the initial, shift, equilibrium chart. Once you know the equilibrium concentrations, you can calculate K_eq using the expression you wrote in the introduction.
   6. Data analysis, evaluation, and conclusion as usual, per the lab format handout. Questions:
      
      1. What assumption was made to find [FeSCN⁺²] in the standard test tube?
      2. Try to find K_eq using data from tube #1. What is the problem?
      3. What error becomes greater as you progress to tube #5?
3. Rate of Reaction Lab
   1. Introduction/Background: The purpose of this lab is to find how varying the concentration affects the rate of a reaction. Include in your background factors that affect reaction rate, define rate law and order of reaction. The reaction to be studied in this lab is
      H₂O₂ + 2 I^-1 + 2 H⁺¹ ---> 2 H₂O + I₂
   2. Hypothesis: In this lab, the concentration of H₂O₂ will be changed and the rate of production of I₂ will be observed. State how [H₂O₂] will affect the rate.
   3. Procedure:
      1. Obtain two clean, dry, 12 well microstrips.
      2. In one microstrip, add 4 drops H₂O₂ to wells 1-3, add 3 drops H₂O₂ to wells 4-6, add 2 drops H₂O₂ to wells 7-9, and add 1 drop H₂O₂ to wells 10-12.
      3. In the same microstrip, add 1 drop water to wells 4-6, add 2 drops water to wells 7-9, and 3 drops water to wells 10-12.
      4. In the second microstrip, to each well add 4 drops starch solution and 1 drop I^-1 solution.
      5. Carefully invert the second microstrip over the first. Shake firmly once to mix. Begin timing. As soon as a color starts to change in a well, record the elapsed time for that well. Continue timing until all the wells have changed.
      6. Rinse out the strips in the sink and shake dry.
      7. Repeat steps 2-6 for a second trial.
      8. For each trial, average the time in wells 1-3, then wells 4-6, 7-9, and 10-12.
   4. Data: Set up a chart for two trials, though you may end up doing more, depending on what your data looks like.
   5. Data Analysis: Graph average time (y-axis) vs. # of drops of H₂O₂ (x-axis) for each of your trials. You can put them on one set of axes. Do the graphs make sense? Discuss the results in terms of how concentration of H₂O₂ affects the rate.
   6. Evaluation and Conclusion as usual, per the lab format handout. One question: How would you find out if [I^-1] affected the rate? Describe the experiment and what results you would see if the rate was zero order for I^-1.

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