Why is food coloring getting through our science fair filter?
April 24, 2013 2:44 PM Subscribe
Why is food coloring getting through our science fair filter?
So the kid and I made a science fair water filter. 2L soda bottle turned upside down and packed with rocks, gravel, sand, silt, cotton, and pet-store activated carbon.
We mixed water and food coloring (red) and put it through the filter. The filter is pretty slow (1oz/minute). The water came out slightly lighter red.
Several passes of water later and all the red dye has flushed out and clear water in comes out as clear water.
I thought for sure that the filter would hold the red dye. What am I missing?
So the kid and I made a science fair water filter. 2L soda bottle turned upside down and packed with rocks, gravel, sand, silt, cotton, and pet-store activated carbon.
We mixed water and food coloring (red) and put it through the filter. The filter is pretty slow (1oz/minute). The water came out slightly lighter red.
Several passes of water later and all the red dye has flushed out and clear water in comes out as clear water.
I thought for sure that the filter would hold the red dye. What am I missing?
No filter will be perfect, but here's where you get to do some fun science with real-world, practical uses: Try adjusting the temperature and acidity of the untreated water, and then measure how much dye you get in the treated water.
If you have a spectrometer, you could use that to measure dye concentration in the treated water bottle. However, another easier way that doesn't require special equipment is to measure the amount with a "dilution"-based gauge.
The amount of dye you start out with is your "100%" measurement — take a picture of the water with this amount of dye in it. Print this photo to a color printer.
Then dilute the water to a 50% strength: Take out half of the original dyed-water and put it in a soda bottle with the rest filled with clear water. Take a picture of the water with this 50% dilution of dye-water mix. Print this photo to a color printer.
Repeat these dilution-and-print steps another 3-4 times. This gives you the color of the water with dye at 100%, 50%, 25%, 12.5% and 6.25% strength (or even more dilution, depending on how many dilution steps you go through).
Set up your filter as normal. Measure the temperature of the untreated water. Look at how much dye gets through the filter and into the treated water bottle after some set amount of time: Next, hold your photographic gauge up to the treated water bottle to estimate the dilution factor with "normal" conditions, matching up the color to the dilution amount.
Now set up your filter again, but warm up the untreated, dyed water first. Say, another 10 degrees Fahrenheit. Again, measure the temperature of the untreated water. Look again at how much dyed water gets through in the same amount of time, using your photographic gauge to estimate how much dye got through with the warmer water.
Repeat the experiment with even warmer water. Or, go the other way: Cool the water down and see if this changes how the filter works.
This gives you some data points to plot on a chart: for a given temperature x, you get an estimated dilution of y. Is there a trend? Do warmer water sources allow the filter to work better or worse?
You could repeat this by changing the acidity of the dyed water, using litmus paper and chlorine from a swimming pool supply shop to measure the acidity of the dyed water. Does more dye get through the filter as you add more chlorine, or less?
Again, you end up with a graph of data points measuring acidity vs dye adsorption. Now you can see if there is a trend with how much better or worse the filter works when you change the acidity of the dyed water.
posted by Blazecock Pileon at 3:06 PM on April 24, 2013 [13 favorites]
If you have a spectrometer, you could use that to measure dye concentration in the treated water bottle. However, another easier way that doesn't require special equipment is to measure the amount with a "dilution"-based gauge.
The amount of dye you start out with is your "100%" measurement — take a picture of the water with this amount of dye in it. Print this photo to a color printer.
Then dilute the water to a 50% strength: Take out half of the original dyed-water and put it in a soda bottle with the rest filled with clear water. Take a picture of the water with this 50% dilution of dye-water mix. Print this photo to a color printer.
Repeat these dilution-and-print steps another 3-4 times. This gives you the color of the water with dye at 100%, 50%, 25%, 12.5% and 6.25% strength (or even more dilution, depending on how many dilution steps you go through).
Set up your filter as normal. Measure the temperature of the untreated water. Look at how much dye gets through the filter and into the treated water bottle after some set amount of time: Next, hold your photographic gauge up to the treated water bottle to estimate the dilution factor with "normal" conditions, matching up the color to the dilution amount.
Now set up your filter again, but warm up the untreated, dyed water first. Say, another 10 degrees Fahrenheit. Again, measure the temperature of the untreated water. Look again at how much dyed water gets through in the same amount of time, using your photographic gauge to estimate how much dye got through with the warmer water.
Repeat the experiment with even warmer water. Or, go the other way: Cool the water down and see if this changes how the filter works.
This gives you some data points to plot on a chart: for a given temperature x, you get an estimated dilution of y. Is there a trend? Do warmer water sources allow the filter to work better or worse?
You could repeat this by changing the acidity of the dyed water, using litmus paper and chlorine from a swimming pool supply shop to measure the acidity of the dyed water. Does more dye get through the filter as you add more chlorine, or less?
Again, you end up with a graph of data points measuring acidity vs dye adsorption. Now you can see if there is a trend with how much better or worse the filter works when you change the acidity of the dyed water.
posted by Blazecock Pileon at 3:06 PM on April 24, 2013 [13 favorites]
And don't forget that the filter materials will have a limited capacity for absorption. Does the same amount of dye come through on the second run? The tenth? The hundredth?
(great ideas, BP!)
posted by firesine at 3:49 PM on April 24, 2013 [2 favorites]
(great ideas, BP!)
posted by firesine at 3:49 PM on April 24, 2013 [2 favorites]
Response by poster: Blazecock - Awesome. Did I mention it's a 1st grade science fair? :)
I think I should have titled this post, "The filter, it does nothing", because of how little change there was in the color of the of the water pre- and post-filter. One of our sources for the for our experimental set up suggested there would be 100% filtration of the red dye. Instead there was almost none.
Is there a physical/chemical explanation for this? For example, food dye is is made up of ??? that is unaffected by particulate filtration and not chemically reactive with activated carbon.
posted by elmonobonobo at 4:01 PM on April 24, 2013
I think I should have titled this post, "The filter, it does nothing", because of how little change there was in the color of the of the water pre- and post-filter. One of our sources for the for our experimental set up suggested there would be 100% filtration of the red dye. Instead there was almost none.
Is there a physical/chemical explanation for this? For example, food dye is is made up of ??? that is unaffected by particulate filtration and not chemically reactive with activated carbon.
posted by elmonobonobo at 4:01 PM on April 24, 2013
If you can find the name of the dye, post it here. I'll do a bit of searching and see if I can find anything.
posted by Blazecock Pileon at 4:07 PM on April 24, 2013
posted by Blazecock Pileon at 4:07 PM on April 24, 2013
This can be a teaching moment about the importance of "publishing" negative results. The experiment isn't a failure at all! It shows that this filter does nothing! That is a valid result...(I know that it's first grade and all) but Science is a process. You would totally impress me at a science fair if you set up the filter, shows that it doesn't work, then have"future research needs" like, well let's try other things and see what the filter could work for, or alternatively, what could collect the dye? Maybe even hint about how that one time a sock got red in the laundry, hey what if we filled it with socks! Anyway my point is that it's more about the thinking process of an experiment, than the actual results. (and that it's really a big issue in science that only positive "exciting" results get published)
posted by dipolemoment at 4:10 PM on April 24, 2013 [5 favorites]
posted by dipolemoment at 4:10 PM on April 24, 2013 [5 favorites]
Response by poster: I'm away from the kitchen now, but it was a food grade red dye that was bought at a craft store for cupcakes. (Maybe this). The colored frosting that resulted turned our tongues quite red.
posted by elmonobonobo at 4:14 PM on April 24, 2013
posted by elmonobonobo at 4:14 PM on April 24, 2013
The color-conferring part of the Allura red food coloring molecule is doubly ionized in water solution, and activated carbon isn't so good at pulling ions out of water, probably because the carbon can't get near them because of their bodyguard of water molecules (which is already maximally absorbed as water pours through).
The water sticks tight to ions because it's a polar molecule.
posted by jamjam at 4:15 PM on April 24, 2013 [5 favorites]
The water sticks tight to ions because it's a polar molecule.
posted by jamjam at 4:15 PM on April 24, 2013 [5 favorites]
That's a great point. You could try different brands of activated charcoal, too. Maybe the particular stuff you're getting from the pet shop is not very good at filtering out dyes, and there is better stuff out there. That would affect those temperature and acidity experiments too — how could you control for the quality of filter you're using in the experiment (in other words, how does the quality of filter affect the results)? How might that affect fish people keep as pets? Or cleaning wastewater from a clothing factory? These are good questions for a science fair project to ask.
posted by Blazecock Pileon at 4:15 PM on April 24, 2013
posted by Blazecock Pileon at 4:15 PM on April 24, 2013
Activated carbon forms relatively weaker (van der Walls) interactions with the ionic dye molecules than the polar water will. Probably, even if the charcoal picks up some dye at high concentrations, dye-free water will strip it back out.
posted by pullayup at 4:25 PM on April 24, 2013 [1 favorite]
posted by pullayup at 4:25 PM on April 24, 2013 [1 favorite]
There are two things going on in "filtration" systems. Filtration, which is good old fashioned "big things won't fit through small holes" physics and chromatography, which is what jamjam is alluding to.
In the citadel of science where you have a pump that can flow at 2.35 mL/min (because 2.4 is too fast) and a column packed with a handful of resin has a surface area equal to 27 football fields, you load a mixture of chemicals onto a column and then force them off with a gradient of increase pH, salt or dissolved organic solvent concentration. The reason there are several different ways to do this is not all solid and mobile phases (in your case charcoal and water) will work well with all molecules.
Also, is your activated charcoal in the form of little rocks? Part of the problem is likely due to that 27 football fields thing I mentioned. Molecular interactions take place over very small distances and if you're not using a cake of powdered charcoal a lot of dye is going to get through without coming anywhere near the reaction distance of the activated charcoal.
posted by Kid Charlemagne at 5:28 PM on April 24, 2013
In the citadel of science where you have a pump that can flow at 2.35 mL/min (because 2.4 is too fast) and a column packed with a handful of resin has a surface area equal to 27 football fields, you load a mixture of chemicals onto a column and then force them off with a gradient of increase pH, salt or dissolved organic solvent concentration. The reason there are several different ways to do this is not all solid and mobile phases (in your case charcoal and water) will work well with all molecules.
Also, is your activated charcoal in the form of little rocks? Part of the problem is likely due to that 27 football fields thing I mentioned. Molecular interactions take place over very small distances and if you're not using a cake of powdered charcoal a lot of dye is going to get through without coming anywhere near the reaction distance of the activated charcoal.
posted by Kid Charlemagne at 5:28 PM on April 24, 2013
The dye you linked to is concentrated to give intense colors. You might try repeating the experiment with cheap grocery food coloring. My sister had some food coloring paste for icing that I would have had to use half a bottle of cheap stuff to even come close to the same intensity.
posted by stray thoughts at 5:31 PM on April 24, 2013
posted by stray thoughts at 5:31 PM on April 24, 2013
Re the food coloring - try wholesome all natural type food coloring. I bought some all-natural red food coloring at an organic grocery store when I was making red velvet cupcakes. They just came out a kind of pinky brown. Whereas the unnatural ;) cheap grocery store food coloring makes lovely vivid red cupcakes.
posted by Joh at 10:11 PM on April 24, 2013
posted by Joh at 10:11 PM on April 24, 2013
It could be the activated charcoal if it already soaked up what it could during its life on the shelf.
It's a teachable moment. I would try other dyes, or tasteable tumeric or garlic with that charcoal. And try other charcoals.
posted by sebastienbailard at 12:07 AM on April 25, 2013
It's a teachable moment. I would try other dyes, or tasteable tumeric or garlic with that charcoal. And try other charcoals.
posted by sebastienbailard at 12:07 AM on April 25, 2013
Echoing the "try 'organic' food coloring" suggestion. It can be pretty weak, I use up almost a whole bottle of the stuff coloring buttercream frosting if I want anything more intense than a pastel shade.
posted by lyra4 at 5:44 AM on April 25, 2013
posted by lyra4 at 5:44 AM on April 25, 2013
Nthing turning the project into a discussion of how the researchers' expectations were overturned by the data.
In high school I did an experiment trying to test the efficacy of jewelweed on preventing poison ivy dermitis. My final paper was on the discovery (at least, for our class) that mice are immune to poison ivy dermitis.
And don't like jewelweed at all, which is odd, because it's a tasty green to humans.
posted by IAmBroom at 7:56 PM on April 28, 2013
In high school I did an experiment trying to test the efficacy of jewelweed on preventing poison ivy dermitis. My final paper was on the discovery (at least, for our class) that mice are immune to poison ivy dermitis.
And don't like jewelweed at all, which is odd, because it's a tasty green to humans.
posted by IAmBroom at 7:56 PM on April 28, 2013
This thread is closed to new comments.
posted by KathrynT at 2:54 PM on April 24, 2013