Acids and Bases

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MODULE

2

ACIDS AND BASES

In Module 1, you identified common properties of solutions using different methods. You learned how to report the amount of the components in a given volume of solution. You also found out that not all solutions are liquid. Some of them are solids and others are gases. Towards the end of the module, you investigated the factors that affect how fast a solid dissolves in water. Most of the solutions you studied in Module 1 form two classes or groups of materials that are related to each other and are important in daily life. They have common properties that can easily be identified. What do you think are common properties among vinegar, calamansi juice, and soft drinks? What are common among liquid sosa (drain cleaners), soaps, and detergents? Which among these are called acids? Which are classified as bases? In this module, you will investigate the properties of acids and bases using an indicator, a dye that changes into a specific color depending on whether it is placed in an acid solution or in a basic one. Aside from knowing the uses of acids and bases, you will also find out the action of acids on metals and think of ways to reduce the harmful effects of acids. Knowing the properties of acids and bases will help you practice safety in handling these solutions, not only in this grade level, but in your future science classes.

How acidic or basic are common household solutions? Does water from different sources have the same acidity? What is the effect of acid on some familiar metals?

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Activity 1 How can you tell if a solution is an acid or a base? Acids and bases are all around us. How will you know if a solution is an acid or a base? In this activity, you will distinguish between acids and bases based on their color reactions to an indicator. An indicator is a dye that changes into a different color depending on whether it is in acids or in bases. There are many indicators that come from plant sources. Each indicator dye has one color in an acidic solution and a different color in a basic solution. A common indicator is litmus, a dye taken from the lichen plant. Litmus turns red in acid solutions and becomes blue in basic solutions. You will first make your own acid-base indicator solution from plant indicators available in your place. This is a colorful activity. You may select a local plant in your community. You can use any of the following: violet eggplant peel, purple camote peel, red mayana leaves or violet Baston ni San Jose. These plant materials contain anthocyanins. These plant pigments produce specific colors in solutions of different acidity or basicity. In this activity, you will: 1. Prepare a plant indicator from any of the following plants: violet eggplant peel, purple camote peel, red mayana leaves or violet Baston ni San Jose; 2. Prepare indicator paper using the plant indicator; and 3. Find out if a given sample is acidic or basic using the indicator.

TAKE CARE!

It is dangerous to taste or touch a solution in order to decide if it is an acid or a base.

Grade 7 Science: Matter Diversity of Materials in the Environment

2

Part A. Preparation of Indicator* In this part of Activity 1, you will prepare a plant indicator that you will use to determine if a given material is an acid or a base. Materials Needed 1 pc mature, dark violet eggplant or camote leaves of Mayana or Baston ni San Jose alum (tawas) powder sharp knife or peeler small casserole or milk can plastic egg tray or small transparent plastic cups brown bottle with cover alcohol lamp tripod Procedure 1. Peel an eggplant as thin as possible. (You may also use the skin of purple camote or the leaves of red mayana or Baston ni San Jose.) Cut the materials into small pieces and place in a small casserole or milk can. You may keep the flesh of the eggplant or camote for other...
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