In this group of experiments we learned that the amount of acid or base in water is an important thing to know for many reasons. Scientists (and students of science) use a number system called pH to measure and calculate the amount of acid in a material. We learned that the opposite of acid is base, and that acid and base will react and neutralize one another. A solution is neutral when the amount of acid is equal to the amount of base, and there is very little of either one.

We also learned that some substances change color when the amount of acid or base changes. These substances are called pH indicators. The indicator we used is the juice of the red cabbage.

We learned that although very strong acids or bases can be dangerous, and can burn the skin or eyes, there are many things used in the home that are mild acids or bases that are used for food or medicine.

Cool Stuff You Can Do 

Make your own Test Strips — With the help of an adult, cook ¼ cup of red cabbage in ¼ cup of water for a few minutes until the water is highly colored. Cool, and pour the juice through a coffee filter in a funnel into a bottle, rinsing the cabbage once with a small amount of water. This liquid can be used to test things to see if they are more acid or basic. Remember that an acid material (like vinegar) will turn the juice red, and a base like bicarbonate of soda will turn it blue or green. You may also wet a piece of coffee filter with the juice, and place it on a flat surface to dry. Cut the paper into strips the size of a Popsicle stick. These strips can be used to test for acid or base by wetting the paper with the material to be tested, and observing the color change.

The juice contains a lot of carbohydrates (food) and will spoil, so store it in the refrigerator when not being used. The juice on the paper should last a long time if it is kept dry and in the dark.

Make some Carbon Dioxide — Put a piece of clam shell or oyster shell into a small clear glass or plastic cup. Add a tablespoon of vinegar and enough water to cover the shell. You should see some bubbles coming from the shell. This is carbon dioxide, the same gas that comes from carbonated soft drinks. Sodium bicarbonate was once used to make these kinds of drinks, so they are sometimes called "sodas." If you remove the shell after the bubbling has stopped, and let some of the liquid dry up overnight, you will see crystals of calcium acetate. You can also test eggshells (from boiled eggs) and some small stones. If the stone bubbles, it is probably limestone.

The "fizz" of an Alka-Seltzer is from the reaction of aspirin (an acid) with sodium bicarbonate to release the carbon dioxide bubbles.

Find Other Test Materials — Make two test solutions by dissolving a teaspoon of sodium bicarbonate in a glass of water (your base) and again by dissolving a tablespoon of vinegar in a glass of water (your acid). These can be used to discover other materials that are acid-base indicators. Blueberry juice will work, but grape juice will not! Other things to try include; fall leaves, blackberries, and the skins of apples, plumbs, or cherries. Just mash them up, make piles on two saucers, add a teaspoon of the test solutions to them, and look for changes in the color.

Look for references to pH in news, magazine articles, on television, or in advertising. It is important in growing plants, maintaining an aquarium, or maintaining a swimming pool. Remember a pH of 7 is neutral, a pH lower than 7 is acid, and a pH greater than 7 is basic.