The Cool Blue Light of Luminol

[deleted-310350]

Hey Terik,

Thanks so much for your help! I really appreciate it. I just really can't stop feeling frustrated about this project of ours. I'm just really thankful that you are trying to help us. Anyways about the project we tried to freeze the hydrogen peroxide but it was too frozen to use, so we need to defrost for a few days. Did we do anything wrong? poohh. So stressed.

Sincerely,
Shin

[deleted-294464]

Terik and Shin,

Let me chime in with my two cents as another expert. You two have already covered quite a bit of ground, but let me see if I can help clarify a bit.

As you know, the blue glowing is caused by a series of reactions that all need to occur (see the background information of the experiment for drawings of each molecule).

1. Luminol becomes the dianion in the presence of OH-......This essentially means that luminol becomes a dianion at basic pH levels.

2. One form of the dianion luminol will react with O2 to form 5-amino phthalic acid.

3. The O2 is formed by a metal catalyst (iron or copper) reacting with a peroxide (hydrogen peroxide or sodium perborate)

4. The 5-amino phthalic acid is what will glow as it 'relaxes'.

I am not completely sure, but I think I know why the glow is not lasting long. In the experiment they suggested, sodium perborate is used to form oxygen in the presence of copper sulfate. You guys are correct, hydrogen peroxide will also form oxygen in the presence of copper sulfate.

However, the sodium perborate does something else in the reaction that is not mentioned. Sodium perborate in water will make a basic pH solution (pH ~ 10). So sodium perborate allows step 1 above to actually occur. Hydrogen Peroxide does NOT make a basic solution in water (pH ~6). So using hydrogen peroxide in your solution will reduce the amount of luminol in the dianion form, since step 1 will not really occur in any appreciable amount. To make a strong glow, my best guess would be that sodium perborate should be ordered (perhaps ordering the cool blue light experiment kit from Edmunds scientific for $10 if extra funds are available?)

Hope this helps to clarify.

Josh

[deleted-310350]

Hey Josh,

Well it was really nice of you to join Terik into helping me. First of I really didn't get what OH means. And ahmmm can you explain #'s 2-4 again because I was really lost. Thanks sooooo much!

Sincerely,
Shin

[deleted-294464]

Shin,

Sure, let me see if I can clarify it a bit.

When I refer to OH-, I just refer to the molecules that are around in a basic solution. OH- is just an oxygen atom which is connected to a hydrogen atom with an extra electron present. The connection between the two is known as an oxygen-hydrogen bond. Solutions can be either acidic (an example is orange juice) or basic (one example is almond milk). Acidic solutions have more H+ molecules present. Basic solutions have more OH- molecules present. The + and - refer to the charge on the molecule. If it is + charge, that means there are more protons than electrons. If it is - charge, that means there are more electrons than protons.

The first step to making luminol glow only works if luminol is in a basic solution, because the OH- molecules react with luminol to make a new molecule (lets call this new molecule "dianion luminol").

In steps 2-4, the dianion luminol interacts with a series of molecules to cause the blue glow. The series of molecules include hydrogen peroxide (or sodium perborate) and copper (or iron).

The problem with your reaction isn't with steps 2-4, because you have copper and hydrogen peroxide present with luminol. The problem is with the first step, since you are not making dianion luminol because hydrogen peroxide makes an acidic solution. If you switch to sodium perborate, the experiment will work better, since sodium perborate makes a basic solution, so step 1 actually occurs.

I hope this clarifies a bit, but let me know if you still have questions.

Josh

[deleted-310350]

Hey Josh,

Thank you for explaining. I really don't understand electrons and protons yet because we haven't tackled that topic in science class yet. But we are about to when we get back to school, since we are currently in Thanksgiving break. But anyways thanks you so much for your help and I'll keep you and Terik posted about what happens in our experiment. When we freeze the hydrogen peroxide should it come out frozen or it should be still melted? like how long should we freeze the peroxide?

Sincerely,
Shin

[deleted-310350]

Hey Josh and Terik,
Well it seems like, you guys haven't answered my emails. But that's okay... ahmm we have a lot of questions for you guys and her it is!

-- We purchased 1 pound of copper sulfate and 1 pound of luminol, but we think Amazon forgot about the luminol and we might not be able to get it in time because it is weeks late. After saying that, should we just do small measurements of everything when doing the experiment? Would the results be the same? Would it be easier to see the luminescence in a photo we would take to show the judges for proof if the measurements were bigger?
-- Our science teacher said that our data table would need to have a range of luminescence that we create to compare different trials. We think that means on a scale of 1 to 10 that we make up. Do you have any more tips on how to make a great data table that shows a lot of information to summarize our results?
-- When we experimented to see if the real experiment was going to work, we just used an iphone to take pictures to the glow, but it didn't work so well. We could barely see anything and we doubt this will count as accurate proof. What kind of camera should we use to get the best look for a picture?
-- We are going to freeze the hydrogen peroxide like we were told, but do you mean "all the way frozen or just make it cold? Should we not do any to the peroxide at all?
-- We were going to purchase some latex gloves and clear plastic cups for our experiment. Is there anything else we should purchase to help prep?
-- We were planning on doing the actual experiment Sunday the 13th, and (or) possibly in early January. It would be great if you got back to us as soon as possible because we need your expert advice. Thanks so much!

These are actually my partner's questions....

Sincerely,
Shin and Katelyn

P.S. please answer immediately, we need these questions answered ASAP....

[deleted-2131]

Hi 2shin,

The option that will give you the highest chance of seeing a strong effect is to follow the procedure in the Crime Scene Chemistry project idea.

https://www.sciencebuddies.org/science- ... p078.shtml

We've referenced this procedure (as well as the instructions that come with the Cool Blue Light kit) several times now. Anytime that you change the procedure from the ones described in those documents, you increase the chance that you won't see the result that you are looking for. Use the chemicals described in those procedures in the amounts described in those procedures, with the exception of varying the amount of copper sulfate as we discussed previously, if you still want to see the effect of copper sulfate abundance. As Josh pointed out, you need to use perborate to get the right conditions to make the luminol glow strongly.

With regards to your data table, follow the directions in the Crime Scene Chemistry project idea and set up a digital camera to measure the glow. The "analyzing your results" section of the procedure for that project idea explains how to make a data table for your results. As you discovered, an iPhone camera probably won't work particularly well. A point-and-shoot digital camera or a dSLR camera would probably both work better than your iPhone camera. It will be really important to have a tripod (or some other stable structure) for holding the camera. If you move the camera during the exposure, the picture will look blurry.

I'm not sure why you are freezing the peroxide. I don't think you need to. As Josh and I have mentioned earlier, you will get better results if you use perborate instead of hydrogen peroxide.

With regards to what to purchase, gloves and cups are good ideas. It would also be good to make sure you have everything listed in the Crime Scene Chemistry materials list.