Science Buddies: "Ask an Expert"

Hi,
I’m working on a science fair project about how differences in temperature cause luminol to react. (“Crime Scene Chemistry—The Cool Blue Light of Luminol”) I hypothesized that luminol would be brighter in the hot water (65℃). Since heat produces energy and chemical reactions require energy, I assumed that the heat would speed up the molecules and the chemical reaction would happen more quickly and more actively with hot water. However, the luminol was actually brighter in the cold water (0℃). Here are my questions

1. Could you explain to me why this happened? Here is the procedure of my experiment and the chart which shows the results.
<procedure>
1. Set out the two clear plastic cups that came with the kit.
2. Add one scoop each of luminol and perborate mixtures and a few copper sulfate crystals to each cup.
3. Add 1/3 cup of ice-cold water to a styrofoam cup.
4. Add 1/3 cup of hot tap water (about 50°C) to a second styrofoam cup.
5. Determine the temperature of the water in each styrofoam cup
6. Add the cold water to one of the plastic cups containing the luminol, perborate, and copper sulfate.
7. Add the hot water to the other plastic cup.
8. Start the stopwatch or timer.
9. Dim the lights and observe the light produced by each cup.
10. Take a picture of the two cups. Record the time on the stopwatch or timer at which the picture was taken.

<i attached the result chart>

2. Also, after reaction, I found some other remains. Could you explain about it, please? I attached the picture.

Hello Hahmmyeongjo,

I’m assuming that you’re working on the project described here:

https://www.sciencebuddies.org/science- ... ml#summary

In your project, light is emitted when luminol reacts as outlined in the project background section. The light is a reaction product. When you increase the temperature, the reaction rate should be faster. And you should see a brighter glow in the warm water.

Does the chart attached to your post show your data for the hot and cold water reactions? This chart shows that except for the observations at 10 seconds, the brightness was greater for the hot water. The higher brightness for the cold water at 10 seconds may have been due to some kind of experimental error. Based on the results shown in the chart you could conclude that hot water increased the reaction rate and made the luminol glow brighter. But you may want to repeat your experiment to confirm your results.

I hope this helps. Please ask again if you have more questions.

A. Norman