How can common items found at home be used in chemistry experiments?

Insights

Chemistry is the study of the ways various substances are put together and their reactions under different conditions. It is a science that involves all of one's senses: seeing, hearing, tasting, feeling, and smelling.

Chemistry is the study of matter. Matter can be found in three basic "states" or forms: liquid, such as water, oil, and saliva; solid, such as wood, bone, and stone; or, gaseous, such as oxygen, helium, and methane.

The basic building blocks of matter are the elements. Elements cannot be broken down into simpler matter. Whether in nature or in the laboratory, two or more elements combine chemically to form a compound. The combined form may have different properties from the original elements. For example, when the element oxygen, a gas, combines chemically in one way with the element hydrogen, also a gas, one compound that can be formed is water. As a liquid, it looks and behaves differently from the gaseous forms of hydrogen and oxygen. A chemical change has caused this difference.

Two large and important groups of chemical compounds are acids and bases. Water (H2O or H-OH) is both an acid and a base. As its chemical formula indicates, pure water has equal concentrations of H+ (hydrogen ions) and OH- (hydroxide ions). When the concentrations of those two ions are equal, a substance is called neutral. When there are more hydrogen ions than hydroxide ions, that substance is an acid. The opposite condition (more hydroxide ions) makes a material a base.

Whether a compound is an acid or a base is indicated by its pH or "power of hydrogen," which represents the amounts of acid or base in a solution. Pure water is neutral, and so registers 7 on the pH scale. The lower the reading below 7, the more acidic a solution is. The higher the reading above 7, the more basic a solution is. The pH of lemon juice is about 2.3--acidic; the pH of seawater is about 8.3--basic.

The cabbage-juice mixture used in the Newton's Apple segment contains compounds that change color as the pH changes. Therefore, it can be used as an indicator to show different levels of the pH scale. Litmus paper, which turns red for acidic solutions and blue for basic solutions, or the pH kits used to test aquariums, can also be used as indicators.

Connections

1. Be a chemist at home. What are acids used for in your home? How are bases used in household items?
   
2. What are some of the signs of a chemical reaction occurring? What kinds of chemical reactions happen when you cook?

Vocabulary

compound a substance made up of atoms of more than one element
element a substance composed of only one kind of atom
formula a combination of chemical symbols and numbers that represents the different atoms in a molecule, and that shows which elements are contained in a compound and their relative amounts
ion an atom or group of atoms carrying an electrical charge
matter what things are made or composed of; can be solids, liquids, gases, or plasma

Resources

Farber, E. (1990) The Nobel Prize winners: Chemistry. New York: Salem Press.

Mullin, V. (1968) Chemistry experiments for children. New York: Dover.

Orii, E., and M. Orii. (1989) Simple science experiments with water. Milwaukee, WI: Gareth Stevens Children's Books.

Penrose, G. (1990) Sensational science activities. New York: Simon and Schuster.

VanCleave, J. (1989) Chemistry for every kid. New York: John Wiley and Sons.

Wyler, R. (1987) Science fun with a homemade chemistry set. New York: Simon and Schuster.

Main Activity

You can identify some everyday substances as being acidic, basic, or neutral. You will learn how to test for pH levels.

Materials

• universal indicator paper
• small paper cups
• wooden sticks
• labels
• newspaper or paper towels
• substances to be tested: water from your school; water from home; lemon, orange, and grapefruit juices; acetic acid (vinegar); apple juice; catsup (diluted); ammonia (diluted 1 part ammonia to 10 parts water); borax; soft drinks; milk of magnesia; sodium bicarbonate (baking soda)

Procedure

1. Put some of each substance into a small cup and label the cups according to their contents.
   
   
2. Group the students and provide each group with some of the testing substances.
   
   
3. Direct the groups to test each substance with small 1" strips of indicator paper. (Place the end of a different indicator paper strip in each cup and observe the color changes.) Have the groups record their findings on a chart.
   
   
4. After the findings are recorded, arrange the substances according to their pH levels, from the strongest acid to the strongest base.
   
   
5. Students can compare the color changes seen in the segment to their own results from the activity.
   
   Note: Many foods with high sugar content indicate an acid reaction on indicator paper. The yeast cells functioning in a sugar solution cause this response.

Questions

1. Which substances were acidic and which were basic?
   
   
2. Why did the indicator paper change color??
   
   
3. Test some soil samples mixed with water. Is your soil acidic or basic??
   
   
4. Dissolve dish soap in water and test it. Test again using laundry detergent.?
   
   
5. What effect do you think stomach acid has on some of the germs that enter our digestive tract?

Investigate the effect that oxygen has on the darkening of fruit. Cut an apple in half. Sprinkle a crushed vitamin C tablet over the cut surface of one of the halves. After one hour, observe, compare, and contrast the color of the untreated apple half with the color of the half that was treated with vitamin C. What gas do you think is reacting to the apple? (Hint: vitamin C is an anti-oxidant.)

Investigate the effect that oxygen has on the darkening of fruit. Cut an apple in half. Sprinkle a crushed vitamin C tablet over the cut surface of one of the halves. After one hour, observe, compare, and contrast the color of the untreated apple half with the color of the half that was treated with vitamin C. What gas do you think is reacting to the apple? (Hint: vitamin C is an anti-oxidant.)

The juices of certain plants, such as red cabbage, can be used as a pH indicator. Chop some red cabbage in a blender (keep the lid on and your fingers out while the blades are moving). Place the chopped cabbage in water and heat until the water turns a deep purple. Pour off and save the liquid. Saturate paper towels with the purple liquid solution and allow to dry. Cut the dried towels into strips to use as indicator paper. (If you don't plan to use the paper strips immediately after they dry, place them in plastic bags and put in your freezer to avoid odor.)

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Newton's Apple is a production of KTCA Twin Cities Public Television.
Made possible by a grant from 3M.
Educational materials developed with the National Science Teachers Association.