Feria Cientifica

Acid-Base Indicators
Science Fair Survival Guide
Topics High School, Middle School, Plant Biology, Chemistry
Color Changers
Acid/base indicators are chemicals that help you compare or estimatethe strength of an acid or base by changing color depending on the pH value of a tested liquid. The lower the pH value, the more acidic the liquid. The higher the pH value, the more basic, oralkaline, the liquid.
In this project, you will make indicators from foods, such as red cabbage and various plants. You will determine the affect of acids and bases on the color of indicators and createcolor scales for the different indicators. You will also investigate the effect of soil pH on the color of flowers containing an acid-base indicator.
Getting Started
Purpose: To determine the effect ofacids and bases on red cabbage indicator.
Materials
* pen
* masking tape
* 1-tablespoon (15-ml) measuring spoon
* white vinegar, 5%
* distilled water
* 1⁄2 teaspoon bakingsoda
* three 10-ounce (300-ml) clear plastic cups
* sheet of white copy paper
* red cabbage indicator (see Appendix 6)
* 4 stirring spoons
Procedure
1. Use the pen and tape to labelthe cups "Acid," "Base," "Neutral."
2. Add 1 tablespoon (15 ml) of vinegar to the Acid cup, 1 tablespoon (15 ml) of distilled water and 1⁄2 teaspoon (2.5 ml) baking soda to the Base cup, and 1tablespoon (15 ml) of distilled water to the Neutral cup. Note: Wash the spoon in distilled water and dry it after each use so that you do not contaminate or dilute the contents of the different cups.3. Set the cups on one of the sheets of white paper so that it will be easier to detect color changes.

4. Add 1 tablespoon of red cabbage indicator to each cup. Using different spoons, stirthe contents of each cup. Then observe and record their color in a Red Cabbage Indicator Data table like Table 27.1.

Results
The red cabbage indicator turns red in vinegar, remains purple in...