What are some natural acid-base indicators?

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I have a science project, and so far I can only name red cabbage juice. It'd be real sweet if you can help me name some more! :D
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Nature provides us with pH indicators in the form of plant pigments known as antocyanines, which change color over different pH ranges, depending on source. The indicators derived from red cabbage and red beet are two examples. Red cabbage juice will function over a wide pH range, from as low as pH 1 up to pH 12. The following is a pH color chart for red cabbage...

pH 2=red, pH 4=purple, pH 6=violet, pH 8=blue, pH 10=blue-green, pH 12 = green-yellow.

Red beet juice will change from red to yellow somewhere between pH 11 and 12.

The indicator solutions are prepared by chopping up the red beets or red cabbage into small pieces, preferably by running them through a blender. Then the juice is strained off from the resulting mush, and the mush can also be extracted with water to yield even more of the pigment. The solutions are filtered to remove any remaining plant matter, and can then be used as is, or diluted if the color is too intense. I have no idea for how long such solutions will keep, but stored in a refrigerator they should last for at least several weeks. If your solutions are too dilute, you may be able to concentrate them with gentle heating, I don't know at what temp the pigments will be destroyed, so be careful.

Many other plants extracts can be used as natural pH indicators. See the link below for an extensive list...

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Other Answers (4)

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  • Hong answered 5 months ago
    Grape Juice
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  • #1 answered 6 years ago
    Yams, berries and other "violet" plant materials.
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  • Nombers answered 6 years ago
    The beautiful flower known as hydrangea (which you can see in http://en.wikipedia.org/wiki/Hydrangea ) is a natural acid-base indicator.

    On acidic soil, the flowers turn blue.

    On neutral soil, the flowers are pale cream.

    On alkaline soil, the flowers become pink or purple.
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  • steve_geo1 answered 6 years ago
    Litmus, which comes from a moss or lichen, is pink in acids and pastel blue in alkalies. It turns at pH = 7.

    Turmeric, which you can get in a supermarket spice section, is also an indicator. It changes between yellow and brown, but I don't remember the pH range.

    Boil it in water to a concentrated yellow solution. Pour off the liquid. Cut up strips of coffee machine filter paper, soak them in the solution, and let them dry. When dry, test them is vinegar, ammonia, NaHCO3 solution, and lemon juice.
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