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Discussion Starter · #1 ·
So when I get bored, I go a little overboard. This time I made my own pH strips with some stuff I had around the house. You've probably heard that red cabbage juice can be used as a pH indicator, but you probably didn't know that the Indian spice turmeric can be used as well. I had lots of turmeric (Indian market two blocks away), and all the other stuff just sitting around, so I gave it a try. I extracted the dye/indicator chemical with alcohol and dipped some drawing paper in the liquid. After it dried, I cut it into strips.



In the photo above, the red and yellow is the pH paper, and the blue background is the cutting board I was working on. Turmeric really stains, so be careful. Red indicates base, while the orangeish-yellow indicates acid. The rightmost (orange) quarter of the strip is tank water. Actually, the pKa of curcumin, the chemical in turmeric is 8, so this paper is really only useful for pH 7 - 9ish. Unfortunately, that means that the whole exercise was useless as far as a planted aquarium is concerned, but I had fun, which is what counts.

Materials: 2 Tbsp turmeric, 200 ml rubbing alcohol, funnel and coffee filter (to separate the powdered turmeric from the dye-infused alcohol, and absorbent paper
Total cost: pennies
 

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I'm a cheapskate, so im interested in this ... I understand your method, but i am unclear on how to then measure the pH reading, even if it is limited to pH 7 - 9.
Oh and rubbing alcohol: is that the same as methylated spirits or is it something else

Cheers

Greg
 

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Discussion Starter · #3 ·
Well... If you want to use this paper for real measurements, you'd need to come up with a color chart. If you wanted to do that, you'd have to make or buy pH standards. You could, for instance, make a pH 7.6 standard, and put a drop of it on your paper every time you took a tank reading. If the tank water made the paper more red, then it's more basic than 7.6, if it made it less red, then it's more acidic than 7.6. When I say that the pKa of curcumin is 8, that means that at pH 8 half of the curcumin molecules will be in the red form and half will be in the yellow form. Around that point the color should change rather suddenly. If you were happy with rough accuracy, you could simply dip a strip in your tank and see whether it stays yellow. If it does, then your pH is definitely somewhat less than 8. Does that make sense? It's early in the morning here, so I could have probably found a more eloquent way to write all of that.

BTW, in the US, rubbing alcohol is 70% isopropyl alcohol. Curcumin is soluble in polar organic solvents, (ethanol, methanol, acetone, methylated spirits, etc.) but not soluble in water or nonpolar solvents like paint thinner, white gas, etc.

Good luck, and have fun. If you stain your hands yellow, which you will, it'll go away in a day or two. :icon_wink
 
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