Kick It up a Notch

Syme sprang to his feet, stepping backwards a little, like a chemical lecturer from a successful explosion. 7. K. Chesterton, The Man Who Was Thursday, 

Two major factors that affect the rate of a chemical reaction—the kinetics of the reaction—are concentration and temperature. The effects of both are easily demonstrated using items from our Shopping List and Solutions.  

For the first demonstration, put on your safety goggles and pour a half cup (120 milliliters) of household bleach straight into each of two small clear cups. Be careful that the bleach doesn t splatter, just as when doing the laundry. You may want to wear gloves to protect your hands. Place both cups on a sheet of white paper so the color is easy to observe. Make sure you have a watch or clock in a convenient viewing location. 

Add two drops of methyl red indicator (found in the swimming pool test kit) to the first cup. Immediately after the addition to the first cup, add four drops of methyl red indicator to the second cup. Swirl both cups gently to ensure mixing. Set both cups down on the white paper and note on the paper the time at which the drops were added. The red color present in each cup will fade slowly over the next five to ten minutes as the bleach attacks the dye molecules that are coloring the solutions. When the red color is gone from the cup with two drops, note the time on the paper and turn your attention to the cup with four drops. Note the completion time for that reaction on the sheet of paper. You can empty everything down the toilet bowl, but make sure to avoid splattering the bleach. 

You can watch the color fade because chemical reactions take time. Some reactions are extremely fast and some are extremely slow, but they all take time. The bleach reaction is paced so that we can observe the process without growing old ourselves. You should have observed that the cup with four drops of dye takes longer to react than the cup with two drops. However, it is not twice as long, even though there is twice as much dye to attack. The rate of reaction is affected by varying the concentration, but not always in a direct way. 

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