Lab 19: Effect of Catalysts on Reactions

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Last time we looked at how concentration, temperature and surface area can influence rates of reaction. For this lab, we are going to determine the effects of catalysts on reaction rates.

Reading:  The Home Scientist Lab Topic VI. Session VI-2, pp. 114- 117.

Important note:  we will be using yeast as a source of catalase rather than blood. Please make that change as you write out the procedure in you notebook!

Experimental Title: Lab 19:  Effect of Catalysts on Reaction Rates

Date of laboratory:  October 14, 2014

Purpose: The purpose of this lab is to examine the effects of various catalysts on the rates of reactions.

Introduction:

For this lab, we will speed up the reaction of hydrogen peroxide breaking down into oxygen and water by adding catalase enzyme from yeast. We’ll stop the reaction by adding sulfuric acid to denature the catalase and then titrate the resulting solutions with a dilute solution of potassium permanganate to determine how much unreacted hydrogen peroxide remains in each sample.

In the presence of hydrogen peroxide, MnO4- ions are quickly reduced to Mn2+ ions, and the solution remains a light brown color. As soon as permanganate ions are slightly in excess, the solution assumes a purple color. By determining
the amount of permanganate required to change color, we can calculate the amount of hydrogen peroxide that remains in the samples.

Important equations:
2 H2O2(aq) → 2 H2O(l) + O2(g)

5 H2O2(aq) + 2 MnO4-(aq) + 6 H+(aq) → 2 Mn2+(aq) + 8 H2O(l) + 5 O2(g)

 Hydrogen-peroxide-3D-balls

(Public domain illustration of hydrogen peroxide from Wikimedia)

Special safety concerns for Lab 19:

  • Please use goggles and gloves.
  • If anything spills, please clean it up immediately with a paper towel and let your instructor know.
  • If glass breaks, do not pick it up with your bare hands. Notify your instructor immediately.
  • Be sure to wash your hands when you are finished with this lab

Materials: Include the list on page 114, but substitute yeast for blood.

Procedures:

Write the procedure on pages 115- 116 in your notebooks, substituting “yeast” for blood or “meat juice.”

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We will also look at a few other catalyzed reactions, but you won’t need to include these in your notebook unless you want to do so.

Materials:
◦    Copper II sulfate solution
◦    Clear plastic cup
◦    Salt
◦    Aluminum foil
◦    Thermometer
◦    Plastic spoon
Procedure:

  1.    Place the piece of aluminum foil in an empty cup. Use your fingers to push the foil firmly down so that it lays flat and covers the bottom of the cup.
  2.     Add 5 mL of the copper II sulfate solution to the cup with the aluminum foil.
  3.     Gently swirl the solution for a few seconds and let it stand still. Watch the aluminum for any bubbling or color change.
  4. Carefully place a thermometer in the cup and record the temperature.
  5.  Use your plastic spoon to place a small amount of salt in the copper II sulfate solution. Gently swirl the solution for a few seconds and let it stand still. Watch for any bubbling or color change.
  6.  Carefully place a thermometer in the cup and record the temperature.

If we have time, we’ll also look at iron (III) chloride as a catalyst for hydrogen peroxide, and a reaction between zinc and sulfuric acid.

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Conclusions:

Once you have completed the lab, sit down and write a sentence or two to explain the results.

Discussion:

Record any thoughts you have about the experiments, including:

  • Possible improvements to the procedures or how to tweak techniques
  • How the results differed from your expectations
  • Suggestions for other experiments
  • What key concepts you learned about catalysts

Please leave a comment or send an e-mail if you have any questions before our meeting.

 

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