Instructables
Picture of The Color-Changing Sports Drink
This blue drink turns purple then red/pink upon addition of a citric acid-boosted can of Sprite. It tastes good and has a similar chemical profile to a hypotonic sports drink (also see this homemade sports drink recipe). It's the kid-friendly version of the Color-Changing Martini - and it's much cheaper and more convenient than buying martini ingredients and dry ice. It's basically a classic chemistry demonstration you can drink.

Note: I published this instructable in 2010, but unpublished it while I developed it further as a submission to the American Chemical Society's  Journal of Chemical Education. The article has now appeared, so for those of you who happen to have electronic access to this journal (probably because you are connected through a university network), you can find the manuscript online here.
 
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Step 2: Red Cabbage?

Yes - it has a pH-sensitive anthocyanin in it, which will act as an indicator. We're going to make the drink basic (alkaline) with baking soda (sodium bicarbonate, NaHCO3), then neutralise it with the acid (citric + carbonic) in the Sprite. The extra citric acid is not strictly necessary - the drink will change color to purple without it - but add it and the drink will turn out a bright pink color.
To get the indicator, you can chop up a cabbage leaf and microwave it in a small amount of water, or add boiling water, or blend and strain the cabbage leaf (thanks to groenert for this last tip). You should get a deep purple-colored liquid.
I used the citric acid idk why it's kind of purple, might be the lighting?
Amazing!!!!
Worked so good!! Freaked my younger siblings out
2014, 2:14 PM.jpg2014, 2:14 PM.jpg
makendo (author)  Indestructibility Man10 months ago

Cool, glad it worked. Still looks pretty purple tho - did you just use Sprite without the citric acid?

gluvit11 months ago
Trying this
hotfarts11 months ago
Great stuff. I'm a chemist, and can mess with my non scientist family members with something they can see and taste, then hopefully understand. :-) Thank you!
makendo (author)  hotfarts11 months ago
Cheers, you're welcome. Have fun!
Jane Oreo11 months ago
oh. Color is very good-looking.
Ohnanka1 year ago
Will it still work if I add gin to it first? ;)
makendo (author)  Ohnanka1 year ago
Oh yes
cmanuel13 years ago
Well as jaegerschlager said in the comments of The Morphing Martini (http://www.instructables.com/id/The-Morphing-Martini/step4/Present/), you can also use blueberry.

But will the colour-change be as fast?
makendo (author)  cmanuel13 years ago
Yes, the colour change will be as fast, because the reaction is very rapid. However, exactly what the colour change is will be dependent on the exact identity of the anthocyanins, so it may be less dramatic. However, I just don't know - I may try it next time I have both dry ice and blueberries in the house...
aidylgs3 years ago
Anyone tried dryice instead of vitamin C for the color change or is it a bad idea?
makendo (author)  aidylgs3 years ago
Dry ice works well, see http://www.instructables.com/id/The-Morphing-Martini/
but the color change is less dramatic (carbonic acid is pretty weak).
aidyl makendo3 years ago
Thanks for your reply. My students enjoyed it but you are correct about a VERY SLOW color change.
makendo (author)  aidyl3 years ago
The speed of the color change will likely depend on how much baking soda you add at the start, because you need to neutralize all of it. In the video I posted for the martini, the color-change is essentially complete in about 15 seconds, but I just used a small pinch of baking soda. I'm interested to hear what was "very slow" for you (several minutes?). I agree that the change does need to be reasonably quick for best effect.
aidyl makendo3 years ago
The color change time was a little over a minute. I did use about a tsp of baking soda.
Rocky1227974 years ago
i tryed it
makendo (author)  Rocky1227974 years ago
Good stuff. Did it go red, pink or purple?
Kind of purple-pink
makendo (author)  Rocky1227974 years ago
OK, that makes sense - it's a weaker acid than citric. Hope it was drinkable as well as healthy!
Your son takes it over the top!  SOOO CUTE!

If you didn't have citric acid, could you use a crushed up Vitamin C tablet (the chewable kind)?
 
makendo (author)  AngryRedhead4 years ago
He's a character, all right.
A vitamin C tablet is a really good idea, even though ascorbic acid is weaker than citric - I think an effervescent vitamin C tablet would be neat (provided it was one of the crystal clear types, and didn't have any coloring), because you could drop it in the blue solution and it would bubble and change color slowly (which is always neater somehow than the rapid changes). Whether it would go pink or only purple, I don't know - I hope someone tries it. 
i did
winterfresh4 years ago
Eye-candy + tongue candy = really sweet instructable!

Really sweet instructable = I click Favorite.
makendo (author)  winterfresh4 years ago
Thanks - glad you enjoyed it.