Chemistry is pHun
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Michelle Jones Morgan Park High School
1744 W. Pryor Ave.
Chicago IL 60643
The main objectives of this mini-teach are to familiarize uppergrade students
with the concept of pH, to teach students how to use litmus and pH paper to
determine pH and to make students aware of natural indicators.
For a class the teacher should plan for stations with six samples (2 acidic, 2
basic and 2 neutral) probably use groups of two or three. !!Caution!! Do not
use bleach or bleach containing products. Do not use products that don't list
Baking soda solution Table salt solution
Lemon juice Vinegar
Ammonia/Windex Distilled water
Clear containers (Baby food jars, cups)
Grape juice Fruit punch
Beet juice Red cabbage juice (in rubbing alcohol)
Litmus paper pH paper
Tweezers Paper towels
Activity One: Measuring pH
1. Have stations set up for students ahead of time. Each station should
include labeled cups or jars with six solutions (2 acidic, 2 basic, 2 neutral)
grouped so no one person will test two neutral solutions. The stations should
also have tweezers for each student, instructions, paper towels for spills, and
have small torn pieces of litmus paper and pH paper.
2. Vocabulary- INABP Tests
Indicator- points something out, in this case tells if the solution is acidic,
basic, or neutral.
Neutral- 1) not acidic or basic, 2) equally acidic and basic
Acidic- increases hydronium ion concentration, [H3O+], in water
Basic- increases hydroxide ion concentration, [OH-], in water
pH- 1) scale of acidity, 2) pH= -log[H3O+]
3. After explaining the vocabulary the teacher should explain that there are
stations to test pH. Then show students that by holding any indicator paper
with tweezers and barely dipping it in a solution and then comparing the color
with the provided chart, one can determine if the solution is acidic, neutral or
basic. With litmus paper it is easy to remember Acid turns Red (try to rhyme
it) or remember that Bases are Blue (alliteratiion). With pH paper a chart
should be given and the color can be matched with the colors on the chart and
the pH is estimated by the corresponding number (0-6 acidic, 7 neutral, 8-14
4. Allow the students time to test the solutions at the stations and have them
record results. The class should come to agreement on the results. Ask the
student if there were any surprises. The water may be slightly acidic because
carbon dioxide in the air may dissolve in the water making carbonic acid, the
same acid in soda pop.
Activity Two: Calibration of Natural Indicators
1. Explain to the students that there are other indicators than litmus and pH
paper. Provide them with the examples of the electronic pH meter and juices
listed in materials. (HINT add ammonia or another base to the juices first to
get a wider range of changes and only have one juice at each station).
2. Instruct the student groups to add drops of vinegar to the juice to increase
the acidity and watch for color changes. At each new color the groups should
measure the pH with pH paper.
3. Have the students return to stations, calibrate the juices, and share
results on the board.
4. Clean up.
Activity Three: Drawing Ions
1. Most students will know the formula for water is H2O. This is demonstrated
by drawing the atomic model which looks just like a Mickey Mouse Head. The
large head being the large oxygen atom with a charge of negative two, and the
two smaller ears are the two smaller hydrogen atoms each with a charge of
positive one, therefore, making the total charge zero.
2. For acids hydronium ions are made. The model for this is a Mickey Mouse
with an extra ear (a water with an extra H with a positive one charge making the
total charge of the ion positive one).
3. For bases hydroxide ions are made. The model for this is a Mickey Mouse
with only one ear (one less hydrogen with a positive charge, making the total
charge of the ion negative one).
The activities are for student exposure and I would hope they get a clear idea
of what pH is and how it is measured. I would have the students turn in
observations sheets that record the pH of each solution and the color change and
pH of each juice.
The teacher should give the student a quick review of the vocabulary and how
they relate to solutions used almost every day.
Material pH Material pH
Battery Acid 0 Blood 7.2
Stomach Acid 1 Sea Water 7.8
Lemon Juice 2 Baking Soda 8
Vinegar 2.3 Borax 9
Wine 3.8 Milk of Magnesia 10
Tomatoes 4 Ammonia 12
Black Coffee 5 Bleach 12.3
Milk 6.8 Oven Cleaner 14
Pure Distilled Water 7