Science Project 98

Project Title

How can one test pH values of various household items without using litmus papers?

Project Purpose

The purpose of this experiment is to estimate the pH values of different water-soluble household items using red cabbage juice as an indicator.

School Name

Manzano Day School

Grade

Third

Teacher

Mrs. Kathy Rimsha

How I got interested in the project?

When I was a kid my parents kept on telling me that I don’t ever touch or taste many household items/chemicals because they can be harmful to my skin and may damage sensitive tissues such as my eyes. Now that I am a grown-up, I would like to scientifically know how strong or weak these chemicals are.
I like science, and chemistry is fascinating to me because in many experiments one can see changes in colors taking place due to chemical reactions.
A science experiment book suggested that red cabbage juice could act as a pH indicator, and I thought I would investigate it myself.
It is a fun project for me and my entire family.

Scientific Background

Chemistry is the study of matter. Matter can be found in three basic “states” or forms: liquid, solid, and gaseous. The basic building block 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 or reaction has caused this difference.

Two large and important groups of chemical compounds are acids and bases or alkaline. 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 or protons) and OH- (hydroxide ions). When the concentrations of those two ions are equal, a substance is called neutral. When there are more hydrogen ions, that substance is an acid. The opposite situation (more hydroxide ions) makes a substance 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. The pH scale is a tool for measuring acids and bases. It is a scale that goes from 0-14. The lower the number the more acidic the substance, a pH of 7 right in the middle is neutral and the higher the number the more basic the substance. The color of the pH (litmus) paper matches up with the numbers on the pH scale to tell you what kind of substance you are testing.

The red cabbage juice, used in this experiment, contains compounds (pigments) 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.

Glossary of terms used above:

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 (e.g., H+ is a positive charge, and -OH is a negative charge)
matter	what things are made or composed of; can be solids, gases, or liquids

What materials did I use?

1. ½ head of red cabbage

2. metal grater

3. bowl to boil the shredded red cabbage

4. large wire strainer

5. 16 clear plastic cups

6. 16 plastic stirrers

7. eyedropper

8. 4 different water-soluble samples each from 4 household item groups – food, cleaning products, medicines, and cosmetics and personal hygiene products

What did I do?

Grated the red cabbage into small pieces and placed them in the bowl + water.

2. Boiled the mixture for 20-30 minutes, until the liquid turned to a dark purplish color.

3. Poured the fluid into a glass bowl through a strainer to remove the cabbage. The collected fluid was bluish/dark purple in color.

4. Made 16 different water-soluble household item samples, each in a clear plastic cup.

5. Made a control sample of (neutral) water.

6. Added a few drops of the red cabbage juice to each of the samples, and noted any color changes.

What happened?

The results obtained from the experiment are recorded in the table next page. The results are also grouped into: 1) acidic, 2) basic, and 3) neutral household items; and captured in the three bar charts.

		Acids		Neutral	Bases / Alkalines
Product	Household	PINK	LAVENDER	PURPLE/BLUE	YELLOW	GREEN
Groups	Items	(pH 2-3)	(pH 4-5)	(pH 7)	(pH 8-9)	(pH 10-11)
*Food*	White Vinegar	pH = 3
	Lime Juice	X pH 2
	Ketchup		X pH 5
	Sprite		X pH 4
*Cleaning Products*	Windex					X pH 11
	Laundry Detergent			X pH 7
	Dishwashing Soap			X pH 7
	Clorox				X pH 9
*Medicines*	Milk of Magnesia					X pH 10
	Vitamin C		X pH 4
	Children's Tylenol			X pH 7
	Caladryl			X pH 7
*Cosmetics /*
*Personal Hygiene*	Bathing Soap					X pH 10
	Mouth Wash			X pH 7
	Nail Polish Remover			X pH 7
	Facial Powder				X pH 8
*Water*	Tap Water			X pH 7

What did I learn?

Red cabbage does work as an indicator, like a litmus paper, as suggested by the science book.

2. What are acids used for in my home.

3. What are bases used for in my home.

4. What are neutrals used for in my home.

5. Acids have the following properties:

a. have a sour taste (for example: white vinegar tastes sour because it is a dilute solution of acetic acid; milk turns sour when it spoils because lactic acid is formed; and the unpleasant, sour odor of rotten meat or butter can be attributed to compounds such as butyric acid that form when fat spoils)

b. are corrosive (damages skin)

c. lose their acidity when they are combined with bases (for example, milk of magnesia, an antacid, reduces the stomach acid which causes the heart burn)

6. Bases have the following properties:

a. taste bitter

b. feel slippery

c. become less alkaline when they are combined with acids

7. Acids could be categorized into: a) strong acids – pH values 2-3, and b) weak acids – pH values 4-5

8. Bases could be categorized into: a) strong bases – pH values 10-11, and b) weak bases – pH values 8-9

9. Never ever touch strong acids or strong bases because they are very harmful to your body.

10. Bases react with acids to produce salt. The name “bases” comes from the fact that they serve as the “base” for making salts.

11. Mixing equal amounts of similar strength acids and bases produces a neutral substance. When I poured the contents of the white vinegar cup into the windex cup, the color changed from red and green to purple, which is the neutral color of the cabbage juice.

12. Bases and acids neutralize each other. Neutralization of fatty acids in the skin produce soap. This is why bases (e.g., bathing soap) feel slippery.

13. Chemistry is a lot of fun!

Bibliography

Orii, E. and Orii, M., (1989) Simple Science Experiments with Water, Milwaukee, WI: Gareth Stevens Children 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.