The Cool Blue Light of Luminol

[gusgus1229]

How does temperature affects the eerie blue glow created by the chemical luminol? And what is the relationship between luminol and iron?

[gusgus1229]

For a chemical reaction with luminol, where can I get potassium ferricyanide?

[tdaly]

Hi gusgus1229,

To help us Experts help you more effectively, please keep all of the questions related to your Cool Blue Light of Luminol project on one topic. I will answer both this question and your other questions on the topic thread you started earlier.

All the best,
Terik

[tdaly]

Hi gusgus1229,

I'll break my response to your questions into three parts:

1) Where to get potassium ferricyanide.
I suggest talking to your science teacher and asking him or her to order it for you. Alternatively, you can order a kit, like the one listed on the Project Idea webpage, that has all the compounds you need for the project (https://www.sciencebuddies.org/science- ... #materials).

2) Temperature effects.
Since the point of this project idea is to find out the answer to this question, I'm not going to tell you the answer--do the experiment and find out for yourself! However, I suggest doing a review of literature to help you formulate a hypothesis. Your literature search will give you clues to the answer. Here are two suggestions to get you started: First, talk to the chemistry teacher at your high school and ask to borrow a copy of the chemistry textbook. Read the chapter that talks about "reaction kinetics". Second, try a Google search for "temperature reaction rates". You will discover a plethora of information.

3) The role of iron in the luminol reaction.
Iron acts as a catalyst, a compound that speeds up a chemical reaction without being consumed by the reaction. Specifically, iron catalyzes the decomposition of hydrogen peroxide. Without iron (or another catalyst, such as copper) present, the oxidation reaction that leads to luminescence proceeds so slowly that the light emitted is very dim (since fewer photons are being produced per time by the reaction). For a deeper understanding of the role of iron in the luminol reaction, read up on catalysts (your high school chemistry book will discuss these; a Google search also yields helpful results). You can also check out this webpage (http://faculty.virginia.edu/analyticalc ... MINOL.html), which I found by doing a Google search for "luminol iron reaction".

Let us know if we can help you in any other way--I look forward to hearing how your experiments go!

All the best,
Terik

[gusgus1229]

What exactly is in glow sticks? I've made the decision of making a glow stick using different kind of chemicals with luminol. I want to know what is in glow sticks that make the chemical reaction with luminol glow?

[gusgus1229]

What is the "crack" or the "break" in glow sticks that makes it start to glow? Does temperature have an involvement in this? What are the chemicals in glow sticks?

[tdaly]

Hi gusgus1229,

The following article by HowStuffWorks explains the chemical reactions that make glow sticks glow, as well as the physical structure of glow sticks, which directly relates to the cracking or breaking you've mentioned. It will be a good starting point for answering the questions you have about the chemicals in glow sticks and why they crack before starting to glow.

http://science.howstuffworks.com/innova ... stick1.htm

In regards to your question about temperature: Are referring to how temperature affects the "cracking" or "breaking" that happens before the glow sticks illuminates? If so, a key thing to remember (after you read the HowStuffWorks article--specifically p. 3) is that cracking involves breaking glass to liberate the chemicals inside a glass ampule so they can react. At the kinds of conditions we're talking about for this experiment (room temperature and perhaps a few tens of degrees higher) the amount of force it takes to break the glass ampule won't depend strongly on temperature. However, the brightness and duration of a glow stick's light will be quite sensitive to temperature. Did you try a google search to find some articles about how temperature affects reaction rate? If not, here is an article to get you started:

http://chemistry.about.com/od/stoichiom ... onrate.htm

If you have specific questions after reading these articles, or find a particular point confusing, let me know and I will be happy to help you. Just as an FYI, you can typically expect a response within ~24 hours of when you make a post. Sometimes you will get a faster response, but often it takes about a day since we Experts are volunteers. But, we're happy to help!

All the best,
Terik

[gusgus1229]

Why does the light reaction in luminol stop after a certain period of time? How would I expect temperature to affect the amount of light produced in the luminol reaction? And how would temperature affect how long the blue light is produced?

[tdaly]

Hi gusgus1229,

I'm so sorry I did not see this post sooner! Usually I get an email when you reply, but that didn't happen this time (which has nothing to do with you--it's probably a setting that I changed on my account). So, I apologize for keeping you waiting for so long

The luminol reaction is a chemical reaction in which light is one of the products. All chemical reactions are limited by how much of each reactant is available to participate in the reaction. (Reactants are the chemicals that you mix together to make a reaction.) The reaction will happen until one of the reactants gets used up. For example, have you ever mixed baking soda and vinegar together and seen the frothy foam they make? In this reaction, baking soda and vinegar are the reactants. Once you mix them, the mixture will bubble and foam until the acid molecules in the vinegar or the base in the baking soda are used up. Once either the vinegar OR baking soda is used up, the reaction will stop, since you have to have both reactants for the reaction to take place. The same thing will be true with the luminol reaction: the reaction will continue (and emit light) until one of the reactants is completely used up.

After reading the links that I've posted, you hopefully now know that increasing temperature will increase reaction rate. But, while increasing temperature will make the reaction go faster, it won't change how much product the reaction will make. "How much" a reaction makes is controlled by the quantity of reactants. Since light is one of the products of the luminol reaction, increasing temperature will not change the number of photons produced by the reaction (assuming that the amount of reactants remains constant). But, increasing temperature will make the reaction go faster, releasing more photons per time, and shortening the reaction's duration. Since your eyes view something as brighter or darker based on how many photons reach your eye per unit time, increasing temperature (which makes the reaction go faster) will make luminol reaction glow more brightly. The total number of photons produced by the reaction, however, won't change with temperature (again, assuming the amount of reactants remains constant). In short, increasing temperature will make the reaction glow more brightly but last for a shorter amount of time.

All the best,
Terik

[gusgus1229]

How can I measure the light produced from luminol? Why is it that when crime scene investigators use luminol, luminol destroys any other evidence in the crime scene? Does it affect the blood?

[tdaly]

Hi gusgus1229,

Some of the reactants in the luminol reaction (e.g., sodium hydroxide (NaOH), potassium hydroxide (KOH), hydrogen peroxide (H2O2), sodium perborate (NaBO3)) are fairly reactive and break down organic material. The luminol reaction won't destroy all of the evidence at a crime scene (if someone left a glove behind, the luminol reaction won't destroy the glove). But, the oxidizing reagents may participate in other, non-luminol-related, reactions, altering some kinds of evidence.

The procedure for this project describes one way to qualitatively measure the light produced by the reaction:

https://www.sciencebuddies.org/science- ... #procedure.

It is very important for you to have the camera in the same place relative to the cups, as well as to have the same camera settings (e.g., exposure time), for all of your trials. Essentially, by using a long exposure time you are integrating the number of photons hitting the camera's CCD over time. You want to make sure you integrate for the same amount of time; otherwise you can't compare data from different trials.

There are more quantitative (and expensive) ways of measuring the light emitted from a reaction. See, for example:

http://www.comm-tec.com/Library/Tutoria ... nts%20.pdf

You can talk to your science teacher and see if she or he knows of a luminometer or spectrophotometer that could do more precise measurements than you could make with a digital camera.

[gusgus1229]

Other than the Crime Scene Investigators, what are other ways luminol is useful? Is there any other procedures to test how the glow of chemiluminescence can glow more brighter and last longer?

[tdaly]

Hi gusgus1229,

Your question about other uses of luminol is a great topic to research yourself. To get you started, it is also used in some biochemical tests, certain kinds of Western blots, and chromatography. Try a Google search using luminol and one of these words (e.g., luminol chromatography).

The duration and brightness of the luminescence is controlled by the reaction rate. They are inversely related--as you increase reaction rate, the reaction will be brighter, but end sooner. Conversely, if you decrease reaction rate, the reaction will last longer, but it will look dimmer. Are you asking if there are ways other than the procedure in the Project Idea to test how reaction rate affects the luminol reaction?

[gusgus1229]

Is it possible to make my own measurement instrument to measure luminol? Like a specialized camera? Better than an other ordinary camera?

[tdaly]

Hi gusgus1229,

That is a very good question. The short answer is yes, it should be possible to build your own instrument to measure the brightness of the luminol reaction. Essentially, you want to count the number of photons that hit a detector of a certain size over a certain period of time. This is what your digital camera does, but there are much more precise ways of measuring the light emitted by the reaction. This article describes how luminometers work:

http://www.comm-tec.com/Library/Tutoria ... nts%20.pdf

You can also look at the "instrumentation" section of this article: http://www.lumigen.com/detection_techno ... minescence

I suspect you could engineer your own luminometer, for much, much less than the cost of commercial instruments, if you put in the appropriate amount of time and effort. If this is something you want to pursue, we have engineers on the Forums who may be a good resource.