Welcome to this experimental science test. We hope that you will find it interesting and worthwhile. Carefully read through these directions and the directions on the next page before you begin to work.

You may be part of a group for the first part of this exercise. Each group should carry out the experiment and collect the data together, but each student must record the data in his or her own booklet. Be sure to record the data exactly as you observe them. After the data have been collected, each student should answer the questions independently.

After you have finished your experiment and have recorded all of the data, you will be asked to answer some questions about the experiment and the data you recorded. Your answers must be written in this test booklet in the space provided. Make sure that you understand each question before you begin to write. At any time while you are writing your answers, you may look back at the directions for the experiment and the data you collected. Be sure that your answers are written as clearly and neatly as possible.

Before you turn the page, read the list of materials given below and check to make sure that your group has everything listed.

The pH of a solution is a measure of its acidity or basicity. Acids have pH values less than 7. Bases have pH values greater than 7. A solution with a pH of 7 is said to be neutral. A substance whose color depends upon the pH of the material with which it is mixed can be used as an acid-base indicator. Paper that has been treated with an acid-base indicator is called pH paper.

Early chemists used plant pigments as acid-base indicators. If you were in the field and did not have pH paper with you, you could prepare an indicator by boiling the petals or leaves of some plants in water. The vial you received marked "INDICATOR" contains an acid-base indicator that has properties similar to those found in plants.

Determining the color of INDICATOR as a function of pH:

You have been given five liquids whose identities you know (sodium hydroxide, liquid soap, distilled water, vinegar, lemon juice). Using the pH paper, you will determine the pH of each of these liquids. Next, you will add INDICATOR to each of these liquids and will record the color that results. Then, you will make a chart of the color of the liquids with INDICATOR versus the liquids' pH values.

After you have finished with the known liquids, you will determine the pH values of the four liquids (A, B, C, and D) whose identities you do not know, using only INDICATOR and the results of your experiment.

1. Put on your gloves. Be sure to wear them during the entire experiment. BE CAREFUL WHEN USING THE CHEMICALS. DO NOT GET THE CHEMICALS ON YOUR CLOTHES OR SKIN. IF YOU GET ANY OF THE CHEMICALS ON YOUR CLOTHES OR SKIN, WASH IT OFF IMMEDIATELY WITH LOTS OF WATER AND NOTIFY YOUR TEACHER. CLEAN UP ANY SPILLS WITH LOTS OF WATER.

2. In the front of the room are containers of sodium hydroxide, liquid soap, distilled water, vinegar, and lemon juice. Label 5 cups with the marker-one for each of the 5 solutions. Bring the 5 labeled cups to the front to get the chemicals. Place approximately 40 drops (2 ml) of each of the liquids into the appropriately labeled cups.

3. At your work station, dip a piece of pH paper into the sodium hydroxide and match the paper's color to the colors on the chart of pH values. Record the color of the paper and the pH value of the sodium hydroxide in Table 1. Also, record the pH value in the appropriate space in Table 2.

4. Repeat Step #3 with liquid soap, distilled water, vinegar, and lemon juice.

5. Now add about 10 drops (0.5 ml) of the INDICATOR into the cup containing sodium hydroxide, and record the color in Table 2 below. Repeat the procedure for the other liquids.

6. The four unknowns, Solutions A, B, C, and D, are in containers at the front of the room. In clean, labeled cups get a small amount (approximately 40 drops) of each unknown. Add 10 drops of INDICATOR to the cups containing Solutions A, B, C, and D. Record your observations in Table 3 below.

7. When you have finished recording all of your observations on your data sheet, you may pour the liquids down the drain. Wash your lab equipment and sponge off the tabletop. Wash your hands.

Please answer the following questions on your own.

1. Explain how you determined the pH values of the four unknown solutions. Why would you want to determine the pH of a solution?

2. Suppose that you were given a different acid-base indicator-one made from cranberries, blueberries, or red cabbage. How would you test the new juice to see if it would be a good indicator? Include in your discussion what properties you believe would make a solution a good acid-base indicator.

3. Acid rain is a problem in the U.S. and around the world. Acid rain is also responsible for the death of some plants and animals. How could you test the rain in your area to see if it is acidic? Explain the procedure. How could you determine if the rain in your area is more or less acidic than the rain in other parts of your state?