ACIDS AND BASES

Introduction

In the lab on electrophoresis, you determined that red cabbage juice turns red at the cathode and it turns green at the anode. Red cabbage juice is a pH indicator and is used to identify acids and bases by color. Therefore, an acid turns the juice red and a base turns it green. If the substance does not show either color, then that substance is a neutral solution.

Objectives

* The student will identify acids and bases using a pH indicator.

* The student will connect positive and negative ions produced by electrophoresis with ions produced by acids and bases.

Marterials

1. Small bowl or petri dish 5. Baking soda solution

2. Red cabbage juice 6. Water

3. Lemon juice 7. Rubbing alcohol

4. Vinegar

Procedure

Many household items are acids and bases. We will test some of these items.

1. Pour a small amount of the lemon juice in the glass dish.

2. Squirt a few drops of the red cabbage juice on top of the lemon juice.

What color does the lemon juice solution become?

Is the lemon juice an acid or a base?

3. Rinse out the dish and pour a small amount of the baking soda solution into it.

4. Squirt a few drops of the red cabbage juice on top of the baking soda solution.

What color does the baking soda solution become?

Is the baking soda solution an acid or a base?

5. Rinse out the dish and pour a small amount of the vinegar into it.

6. Squirt a few drops of the red cabbage juice on top ot the vinegar.

What color does the vinegar solution become?

Is the vinegar an acid or a base?

7. Rinse out the dish and pour a small amount of water into it.

8. Squirt a few drops of the red cabbage juice on top of the chlorox.

What color does the water solution become?

Is the chlorox an acid or a base?

9. Rinse out the dish and pour a small amount of alcohol into it.

10. Squirt a few drops of the red cabbage juice on top of the alcohol.

What color does the alcohol solution become?

Is the alcohol an acid or a base?

Data

Place all data in the table below.

        Substance          Indicator color            Acid or Base               
       Lemon juice                                                               
  Baking soda solution                                                           
         Vinegar                                                                 
          Water                                                                  
         Alcohol                                                                 

Analysis

1. If a substance is an acid, to what color will the solution change?

2. If a substance is a base, to what color will the solution change?

3. If a substance is neither an acid nor a base, what can you say about the solution?

Conclusion

Suppose you are given 2 unknown substances (a powder and a liquid). How would you determine if the unknown is an acid, a base or a neutral solution?