Date: May 1994

Grade Level(s): 6, 7, 8

Subject(s):

• Science/Chemistry

OVERVIEW: The students will be able show how pH affects their lives.

PURPOSE: Students will learn how to test for pH and understand its relationships to them and their environment.

OBJECTIVE(s): STUDENTS WILL BE ABLE TO:

1. Tell what pH is.
2. Draw and label a pH scale.
3. Tell what the pH of different items is.
4. Explain why its important to understand pH. (Dangers, etc.)

BACKGROUND INFORMATION AND MATERIALS:

pH is the symbol for the degree of acidity or alkalinity (base) of a substance. pH also refers to the potential of hydrogen in a substance. Have students draw and label the pH scale as you discuss it.

pH scale l--l--l---l---l---l---l---l--l---l--l--l---l---l---l 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 ^ Acid (H3O+) Neutral Alkaline (Base, OH-)

As the hydronium ion H3O+ concentration increases the acid concentration increases. For example: a pH reading of 1 is a stronger acid than a pH reading of 6. As the hydroxide ion (OH-) concentration increases the alkalinity increases. For example: a pH reading of 12 is a stronger base than a pH reading of 8.5. pH reading of 7 is neutral. The reaction of an acid with a base produces salt and water. In neutralization, the properties of the acid and base are lost as two neutral substances water and a salt are formed.

You will need the following materials:

1. beakers
2. litmus paper (I would recommend litmus paper that tests 1-12 and litmus paper to test specific ranges- i.e. 1-3, 4-6, 6-8, 8-12).
3. paper towels
4. substance you would like to test. (i.e.: lemons, apples, vinegar, shampoo, bananas, water, eggs, ocean water [if available], milk of magnesia, soap, ammonia, etc.
   IT IS VERY IMPORTANT THAT STUDENTS DO NOT BRING OR WORK WITH ANY SUBSTANCES THAT COULD HARM THEM, SUCH AS BATTERY ACIDS, DRAIN CLEANERS, ETC. REMEMBER A STRONG BASE WILL BURN YOU JUST AS FAST AS A STRONG ACID. PLEASE, PROTECT YOUR STUDENTS.
5. paper and pencil for notes.

RESOURCES:

PHYSICAL SCIENCE TEXT BOOK, CHEMISTRY TEXT BOOK, ENCYCLOPEDIA, ANY OTHER RESOURCES THAT RELATE TO pH THAT ARE AVAILABLE.

ACTIVITIES AND PROCEDURES:

Give each student several pieces of litmus paper that will test pH 1-12. Also, several pieces of litmus paper that will test pH 6-8. The other specific testing pH paper use under you direct supervision. Each group of students should also have access to a pH color bar to compare their exposed paper to after exposure.

Following is a list of substances that are easy to test in the class room. Feel free to test any other substance you like as long as it is safe to the students. Have students expose the material to the litmus paper and take notes.

Substance pH 1. lemons 2.4 2. vinegar 2.9 3. apples 3.4 4. bananas 5.2 5. shampoo 5.7 (some shampoo differ from this) 6. water 6.8-7.2 7. eggs 7.8 8. ocean water 8.5(If you have any) 9. soap 10 10. milk of magnesia 10.4 11. ammonia 11.2 12. etc. etc.

Have students do their tests and compare their results with book charts that show pH. Discuss why there are some differences. Students really have fun with this activity if you give them a little freedom to test all different types of things.

MAKE SURE ALL SUBSTANCES BEING TESTED ARE SAFE FOR STUDENTS TO HANDLE BEFORE THEY COME IN CONTACT WITH THEM.

I have had students test everything from saliva to underarm sweat. They really enjoy this part of the activity. It is really important to discuss the possible dangers of exposure to strong acids or strong base substances.

TYING IT ALL TOGETHER:

CROSS-CURRICULUM IDEAS:

Math: Have students graph the pH of several different substances.

English: Have students write an essay of how pH is used in their everyday lives.