CECsci.181


TITLE:    pH

AUTHOR:   JIM L. TORGERSON, NORTH SEVIER MIDDLE
          SCHOOL, SALINA, UTAH

GRADE LEVEL:   Appropriate for grades 6-8.

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.

History:  Check to see if there has been any accidents
in the area regarding strong acids or strong bases.