science project [particles in a solvent]

Bear in mind I’m not science minded and am undoubtedly not using appropriate terms. Is there a way to determine relative number of particles in a solvent at home, without high tech equiptment?

The experiment: she’s going to make vanilla extract using 4 methods. One with whole beans, one with sliced (once) beans, one with beans chopped, and one with beans food processed into mush. Then, if she can determine how much of the bean has infused in the vodka in each group over set times it should indicate something about surface space vs total mass and how that works. She’s got a whole lot of math and graphs planned.

Is there a way to measure at home by a middle schooler that will have adequate value? I don’t think the measurements have to be really precise as long as the relative measurements between the solvents is consistent.

Thx

If you use the same volume of solvent and the same weight of dry material in each case, you should be able to compare by measuring how much light will pass though a similar-sized and presented sample of each of the solutions - this won’t distinguish between dissolved vanillin and other dissolved substances, but it’s a start.

Can you direct me to a resource that can detail how to do this (materials/procedure)? And does the light measurement give a number result she can use in her math or just ‘less than/more than’ by visuals?

Have you contacted the school or teacher about his project? The vodka bit concerns me. If the project has to be presented at school and someone wanted to get pissy, there could be penalties for bringing booze on school grounds. You could use isopropyl alcohol as a non-drinkable solvent for demonstration purposes, I guess.

I was a science teacher for 26 years and once saw a kid suspended because she brought a knife to school- it came with the fork and spoon in a nifty lunchbox she got as a present.

The simplest possible method would probably be to hold a test tube of the solution in front of a white card and compare this against either a printed colour gradient chart (you might be able to find a suitable one at a paint mixing shop), or an onscreen colour mixer such as this one

Alternatively, use a photographer’s light meter and an LED flashlight (in a darkened room so as to eliminate other light sources)

taking a photo of the tubes against a white card (light so that it doesn’t glare from the tubes) will avoid the difficulty of bringing an alcoholic substance onto school grounds. you might get to bring the alcohol in with permission, maybe all the way up to the school board to avoid getting the science teacher(s) or principal in trouble. or for the display tubes (not the ones done at home) use materials from the science lab.

white card comparison is done for comparisons and ‘out of the sophisticated lab’ measurements all the time, it is good science.

to get a number value besides using the eye would involve methods called densitometry.

Grossly subjective evaluation done blindly: Taste tests done by several (adult) volunteers.

Appreciate the warning. I’ve already emailed the teacher about the etoh issue &, since the actual experiment will be done at home, we’ll use alternate display props if it’s no go.

Another possibility might be to simply evaporate off the alcohol in an open container and weigh the remaining solids that are left behind. This would be another point in favour of using isopropyl alcohol, since it’s more volatile than vodka (i.e., it evaporates more quickly). You’d probably need a scale that’s accurate down to the milligram range to make this one work, though, and you’d lose some fraction of the components that make up vanilla other than vanillin. The advantage, though, would be that your daughter would have concrete numbers to put on her poster if that’s important

Or even a roundabout way assuming you can get a highly accurate scale.
Weigh the beans and infuse them. Then take the beans out, dry them and weigh the remains. Calculate the percent of change.

You can bring these in for the display.

Title edited to indicate subject.

Colibri
General Questions Moderator

i don’t believe that for such a small quantity that weighing the solids extracted or the solids left will product a good results. the weights involved are far too small.

the method used in an analytical lab would be light absorption of the extract.

I’m pretty sure you could build a reasonable light absorption meter using a led light source and a webcam (or even a modern cellphone with camera and led flash and a white reflective surface on the other side of the sample cell).

set the cell up so that your control is about 75% saturation (use a photo editing program that can show a histogram of a captured image). Then try your samples.

Look here for a discussion of the principles - you are only looking at measuring absorption, but the principles are all there. Good luck, and learn some science.

Si

The problem with using a digital camera to perform the light metering is that there may be some inherent brightness and colour balancing or adjustment that can’t be turned off. It might be possible to overcome this by ensuring that the image includes a portion of the normal white background (to the side of the sample) - and perform a comparison against this.

Here’s a thoroughly unformed idea for you: :wink:

Saltwater aquarists use a refractometer to measure the saline levels in their aquariums. I would think that the specific gravity measure could also be used in your experiment, but don’t know a whole lot about them.

http://www.drsfostersmith.com/pic/article.cfm?aid=1304

Hope it helps.

I’d agree (thus the suggestion to not get too near the saturation limit). You could easily calibrate it with some known concentration samples, though.

However, for the OP, many years ago in my Analytical Chemistry class, I had to identify an unknown. It was white, crystalline, and had a distinctive sweet odour. I identified it as vanillin before I even got to the IR Spectroscopy bench. It is clear in solution, although I don’t know what the beans/seeds are like in vodka. You may not get good visible results.

Si

I think you’re right. I’m pretty sure an “extract” is a solution, not a suspension of solid particles. A solution may not have a measurably higher light absorption. (Think about a simple syrup - it doesn’t look any darker than water even though it’s a 50% solution of sugar.) Measuring the light absorption may only tell you how much contamination is in the extract.

Also I suspect the concentration of vanillin is too low to be measured with a refractometer.

Or, let the solutions evaporate in a set of white/clear dishes, and measure the relative colours that way. Another good reason for isopropyl…

If there any access to lab equipment at all at the school? I’d be surprised (and intensely disappointed, honestly) if a middle school science lab didn’t have at least one spectrophotometerlying around. These are easy to use and could help for this project. See if one is available for final measurements, either at your daughter’s school or perhaps at a local college or university.

Without having done a bunch of background research, if I wanted to begin to design a method for determining the concentration of vanillin in an extract from vanilla beans, I would begin with:

Soaking the vanilla beans in a solution of alcohol. Lab-grade ethanol, methanol and isopropanol would probably be good starting places. Ideally, you’d get something as pure as possible, so no “denatured” ethanol. Vodka is pretty pure water and ethanol, but has other stuff in it which might affect the results.

I’d filter the solution that I’ve obtained, to removed any solids that might be floating around in there. At home, a coffee filter would be a good start. There are better filters available for lab work.

I’d then try and quantify the amount of vanillin in the solution. Vanillin absorbs UV light at 308nm (note: that NF monograph is for vanillin powder, redissolved into solution), so taking measurements at that wavelength in a spectrophotometer would be a good first start. Use filtered vodka as a blank to get a baseline and compare to the solution you make. You might want to consider comparing to a store-bought solution of vanilla extract as well, but that might not be all that useful. If you can get a spectrophotometer that is able to scan a range of wavelengths, you can see if you actually are measuring a peak at 308nm. You might have to dilute your solution a few times to get it down to a level you can measure…you’d have to correct for that to figure out your final concentration.

One thing to worry about is what other compounds you are extracting with your solvent. Vanilla beans are made up of a lot of stuff, and some of that most likely is also going to come out of your beans. If your solutions are brown, then you know they are more than just vanillin+vodka, because vanillin isn’t coloured in the visible spectrum (it’s white as a powder, and is colourless and clear in solution). This basic method will not isolate the vanillin or remove the other components, and so your results will be affected by them.
If you have a super-friendly chemistry prof at a local college or university and if you’re allowed (by the rules of the science project) to go all-out, ask about using an HPLC. In the lab, that would be a method I’d go with :wink:

Thinking about this too much… I believe it’s possible to buy nearly pure vanillin powder or solutions from food companies. Look into it - that can be your standard to compare what you make at home to.

If you can get your hands on a blacklight, you might be able to take things a step further with some sort of chromatography technique. You could, perhaps, get a qualitative measure of how much vanillin you have, or at least of how much other stuff you have, if you run something like a TLCon a coffee filter (I’ve done it with Sharpie marker colours, but never with vanillin!). I can go into further details if you want - I really don’t know if this would work. It won’t help you solve the concentration, but it could help to show whether you have any vanillin at all.

…I no longer work as a chemist, but the basics are fun to explore :slight_smile:

But some of the vanillin would evaporate too, wouldn’t it?