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Q & A: Food coloring and celery

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Most recent answer: 10/22/2007
Q:
When you add blue food coloring into water and place a piece of celery into the cup will the blue food coloring be to dense for the celery stalk to absorb?
- Kayla Phillips (age 15)
Linclon Park Academy High School, Ft.Pierce Florida.U.S.A.,
A:
Hi Kayla,

The density of the blue food coloring (or rather, the molecular weight, because when dissolved in water, the total density will be close to that of water) probably won't stop the food coloring from being absorbed by the celery stalk. Some things that might have an effect -- the size of the blue dye particles might be so big that they don't fit into the capillary tubes of the celery (probably not the case for ordinary food coloring), and the miscibility of the food coloring in the water may have an effect. Good food colorings dissolve easily in water (unless you get an oil-based one to be used for coloring oils -- these probably won't be absorbed by celery). Normal food coloring dyes are therefore are attracted to the electrically polar water molecules. They should get dragged up the capillary tubes in the celery along with the water.

I once bought some rather pretty blue flowers at a farmer's market, and was initially surprised to find that the water in my flower vase had turned bright blue after a couple of days. I think they watered the flowers with water laced with blue food coloring to make the flowers more blue than they naturally would be.

That having been said, you can check out on paper chromatography, or if the link goes away sometime, do a web search for "paper chromatography". Different dyes will be attracted more to paper or to water molecules, and this will affect the rate at which they will migrate across a piece of paper through which water is seeping by capillary action. If your blue food coloring is a mixture of dyes, and celery has enough interesting properties, the separate dyes in the food coloring may actually separate in the celery. I suspect that paper will work better than celery for this, but it may happen.

Tom J.

(published on 10/22/2007)

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