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Chemistry science fair project:
Make your own cabbage juice pH indicator


Science Fair Project Information
Title: Make your own cabbage juice pH indicator
Subject: Chemistry
Grade level: Elementary School - Grades 4-6
Academic Level: Ordinary
Project Type: Building
Cost: Low
Awards: None
Affiliation: Canada Wide Virtual Science Fair
Description: Cut a red cabbage leaf into tiny clippings. Put them into a clear cup filled with warm water. After 15 minutes remove the clippings and see that the color of the water changed to purple. To test your indicator add lemon juice, see that the purple water turns pinkish redish. Add baking soda and the pinkish redish color turns purple again.
Link: http://www.virtualsciencefair.org/2005/katw5l0/public_html/
Short Background

A pH indicator is a halochromic chemical compound that is added in small amounts to a solution so that the pH (acidity or alkalinity) of the solution can be determined easily. Hence a pH indicator is a chemical detector for hydronium ions (H3O+) (or Hydrogen ions (H+) in the Arrhenius model). Normally, the indicator causes the color of the solution to change depending on the pH. Solutions with a pH value above 7.0 are alkali, and solutions with a pH value below 7.0 are acidic. Solutions with a pH value of 7.0 are neutral.

pH indicators themselves are frequently weak acids or bases. When introduced into a solution, they may bind to H+ (Hydrogen ion) or OH- (hydroxide) ions. The different electron configurations of the bound indicator causes the indicator's color to change, which allows the pH to be determined by the different colors.

pH indicators are frequently employed in titrations in analytic chemistry and biology experiments to determine the extent of a chemical reaction. Because of the subjective determination of color, pH indicators are susceptible to imprecise readings. For applications requiring precise measurement of pH, a pH meter is frequently used.

Many plants or plant parts contain chemicals from the naturally-colored anthocyanin family of compounds. They are red in acidic solutions and blue in basic. Extracting anthocyanins from red cabbage leaves or the skin of a lemon to form a crude acid-base indicator is a popular introductory chemistry demonstration.

Anthocyanins can be extracted from a multitude of colored plants or plant parts, including from leaves (red cabbage); flowers (geranium, poppy, or rose petals); berries (blueberries, blackcurrant); and stems (rhubarb). An exhaustive list would be beyond the scope of this article.

For More Information: pH K-12 Experiments & Background Information

Source: Wikipedia (All text is available under the terms of the GNU Free Documentation License)


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