Life Science Curriculum 8-12

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Submitted by: Janneal Lopez

Position: N/A

Institution: Azusa Pacific University

Title of Experiment: Acid-Base Indicators

Materials Needed:

2 cups of red cabbage, a blender or food processor, a sieve, white vinegar

cup of laundry ammonia, 2 cups of water, 1 teaspoon of baking soda

lemon juice, sugar, table salt , shampoo , hair rinse, milk of magnesia

antacid tablets, milk, aspirin

Scientific Background of Experiment:

  Aids are materials that have certain properties in common. Bases are other substances with a different set of properties. In these experiments, you will examine some of these properties with materials that are found around your house. In addition, you will learn how to use the pH scale to describe acids and bases.

Methodology:

The most amazing property of both acids and bases is their ability to change the color of certain vegetable materials. A common vegetable whose color responds to acids and bases is red cabbage. The first step in this experiment is to prepare an extract of red cabbage, so you can investigate its color changes. Place about 2 cups of red cabbage cut into 1-inch cubes into a blender or food processor. Add about 1 cup of water and blend the mixture until the cabbage has been chopped into uniformly tiny pieces. Strain the mixture by pouring it through a sieve. This strained liquid, the red-cabbage extract, will be used for exploring acids and bases.

Examine the label of a bottle of white vinegar. The label probably says that it contains acetic acid. This indicates that vinegar is an acid and has properties of an acid. Let's see what effect an acid has on the color of the red cabbage extract. Pour cup of vinegar into a colorless drinking glass. Add 1 teaspoon of red cabbage extract, stir the mixture, and record its color. What is the color of the mixture?

The color of the cabbage extract with vinegar is the color the extract has when it is mixed with an acid. Save the mixture in this glass to use as a guide in the rest of the experiment.

Now examine the effect of laundry ammonia on the color of red cabbage. Pour cup of laundry ammonia into another colorless drinking glass. Add 1 teaspoon of red cabbage extract and stir the mixture. Record the color of the mixture.

Laundry ammonia is a base. The color of this mixture is the color of cabbage extract when it is mixed with a base. The color of cabbage extract indicates whether something mixed with it is an acid or a base. Cabbage extract can be called an acid-base indicator. Save the mixture in this second glass to use as a guide.

Now test the properties of baking soda. Place 1 teaspoon of baking soda in a glass and add cup of water. Stir the mixture until the baking soda has dissolved. Then, add 1 teaspoon of red cabbage extract to the solution. Record the color of this mixture.The colors obtain from the vinegar ammonia and baking soda should all be different.

Red cabbage extract can indicate whether a substance is an acid (like vinegar) or a base (like ammonia). It can also show how strong an acid or a base a substance is. Chemists use the pH scale to express how acidic or basic a substance is. A pH value below 7 means that a substance is acidic, and the smaller the number, the more acidic it is. A pH value above 7 means that a substance is basic, and the larger the number, the more basic it is. Red cabbage extract has different colors at different pH values.

approximate pH

Based on this information, what is the approximate pH of vinegar, baking soda and ammonia? Use the instructions for testing vinegar and ammonia to test the pH of several other household substances such as lemon juice, sugar, table salt, shampoo, hair rinse, milk of magnesia, antacid tablets, milk and aspirin, and then record your observation.

Information adopted from the World Wide Web

 

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