Illuminating catalysts

This exercise is a part of Educator Guide: Built for Speed / View Guide

Class time: 30-50 minutes

Purpose: Testing different catalysts and conditions for the light-producing luminol reaction.

Notes to the teacher: This Teacher Guide is intended to provide an outline of an experiment. You can adapt this activity depending on the level of the students, the amount of available class time and the resources available. For this activity, it is easiest to buy several Cool Blue Light Experiment Kits, ideally one for each group of students working together during the experiment. Each kit contains 5 grams of luminol, 5 grams of perborate, 2 grams of copper sulfate, a small scoop for measuring out the chemicals and a few other accessories. You can also buy the chemicals separately and use common lab equipment.

Luminol and perborate will react in water to produce luminescence, but that reaction is greatly aided by a catalyst. Depending on your preference, students can test different catalysts or they can use the same catalyst but vary other conditions to optimize the reaction.

Students will need light to set up experiments, but dark to see how well the experiments work. Plan to do a lot of flipping of the light switch or have two adjacent rooms, one light and one dark.

Materials:

  • Cool Blue Light Experiment Kit at Home Science Tools (currently $9.95) or the chemicals included in the kit: luminol mixture, perborate mixture and copper sulfate
  • Disposable clear plastic cups or small beaker (about 150 ml)
  • Camera without a flash (cell phone cameras will work well)
  • Thermometers for each group
  • Hot and cold water
  • Colorimetric pH indicator strips
  • Household acids and bases such as vinegar, lemon juice, ammonia, water with baking soda or laboratory acids and bases with varying pH
  • A sheet of instructions outlining the experimental design of your choosing
  • Gloves

Directions:

  1. Each student lab group should get one Cool Blue Light Experiment Kit (or related chemicals); additional small clear cups or beakers; and various catalysts (see Step 4 below) or other conditions to test such as amount of catalyst used for a specific amount of reactants, temperature of reactants or the effect of pH on reaction rate (see Step 5 and Step 6 below).
     
  2. Students can set up several small clear cups, each with one small scoop of luminol, one small scoop of perborate and a half-filled small cup of water. If your students are taking a more quantitative route to this experiment, have them measure and record the mass of the reactants.
  3. Decide on a general procedure that students should use to determine the effect of a catalyst, or help your students determine a sound experimental technique of their own. They need to mix and stir all materials with a catalyst and determine the catalyst’s effect. For example, students can use their cell phones to take photos (without the flash) of the luminescent reactions in the dark so they can compare the relative brightness of the reactions afterward. Be sure to use the same exposure settings for each photo with the phone camera and do not auto-adjust the cameras to the brightness.
  1. If you would like students to test different catalysts, provide them with a number of options, such as:
  • Copper sulfate crystals
  • Shiny copper (pennies)
  • Corroded copper (pennies left in water for a day in advance)
  • Shiny iron or steel (paperclips, bolts, etc.)
  • Rusted iron
  • Blood from raw meat or chicken (the iron ions act as a catalyst)
  • Zinc (zinc washers, etc.)
  • Aluminum (foil)
  • Magnesium sulfate (Epsom salts)
  • Other metals or chemical solutions that contain metal ions

 

  1. If you would like students to test the effects of different temperatures on the catalytic reaction, they can use the same small number or mass of copper sulfate crystals for each cup, but different water temperatures. Provide sinks or other sources of hot and cold water, as well as thermometers. (Generally the hotter the water is, the faster the reaction will proceed.)
  1. If you would like students to test the effects of different pH on the catalytic reaction, they can use the same small number of copper sulfate crystals for each cup but use a variety of solutions ranging from acid to neutral to alkaline instead of using water. Provide colorimetric pH indicator strips and chemical solutions or household acids and bases such as vinegar, lemon juice, ammonia, water with baking soda or laboratory acids and bases with varying pH. (An alkaline solution with a pH around 11 should work best, and acidic solutions should suppress the reaction.) Have students measure the pH of each solution before beginning their experiment. 

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