Scope, Sequence & Coordination
A National Curriculum Development and Evaluation Project for High School Science Education
A Project of the National Science Teachers Association
This project was suppported in part by the National Science Foundation.
Opinions expressed are those of the authors and not necessarily those of the Foundation.
The SS&C Project encourages reproduction of these materials for free distribution.
Scope, Sequence & Coordination
SS&C Research and Development Center
Iowa Coordination Center
Bill G. Aldridge, Principal Investigator
and Project Director*
Dorothy L. Gabel, Co-Principal Investigator
Erma M. Anderson, Associate Project Director
Nancy Erwin, SS&C Project Editor
Rick McGolerick, Project Coordinator
Robert Yager, Center Director
Keith Lippincott, School Coordinator
University of Iowa, 319.335.1189
Evaluation Center
Frances Lawrenz, Center Director
Doug Huffman, Associate Director
Wayne Welch, Consultant
University of Minnesota, 612.625.2046
Houston SS&C Materials Development and
Coordination Center
Linda W. Crow, Center Director
Godrej H. Sethna, School Coordinator
Martha S. Young, Senior Production Editor
Yerga Keflemariam, Administrative Assistant
Baylor College of Medicine, 713.798.6880
Houston School Sites and Lead Teachers
Jefferson Davis H.S., Lois Range
Lee H.S., Thomas Goldsbury
Jack Yates H.S., Diane Schranck
Iowa School Sites and Lead Teachers
Pleasant Valley H.S., William Roberts
North Scott H.S., Mike Brown
North Carolina Coordination Center
Charles Coble, Center Co-Director
Jesse Jones, Center Co-Director
East Carolina University, 919.328.6172
North Carolina School Sites and Lead Teachers
Tarboro H.S., Ernestine Smith
Northside H.S., Glenda Burrus
Puerto Rico Coordination Center**
Manuel Gomez, Center Co-Director
Acenet Bernacet, Center Co-Director
University of Puerto Rico, 809.765.5170
Puerto Rico School Site
UPR Lab H.S.
California Coordination Center
Tom Hinojosa, Center Coordinator
Santa Clara, Calif., 408.244.3080
California School Sites and Lead Teachers
Lowell H.S., Marian Gonzales
Sherman Indian H.S., Mary Yarger
Sacramento H.S., Brian Jacobs
Pilot Sites
Site Coordinator and Lead Teacher
Fox Lane H.S., New York, Arthur Eisenkraft
Georgetown Day School, Washington, D.C.,
William George
Flathead H.S., Montana, Gary Freebury
Clinton H.S., New York, John Laffan**
Advisory Board
Dr. Rodney L. Doran (Chairperson),
University of Buffalo
Dr. Albert V. Baez, Vivamos Mejor/USA
Dr. Shirley M. Malcom, American Association
for the Advancement of Science
Dr. Shirley M. McBay, Quality Education for Minorities
Dr. Mary Budd Rowe, Stanford University
Dr. Paul Saltman, University of California, San Diego
Dr. Kendall N. Starkweather, International
* Western NSTA Office, 394 Discovery Court, Henderson, Nevada 89014, 702.436.6685
** Not part of the NSF-funded SS&C project.
Technology Education Association
Dr. Kathryn Sullivan, NOAA
National Science Education Standard—Physical Science
Chemical Reactions
A large number of important reactions involve the transfer of either electrons (oxidation/reduction reactions) or hydrogen ions (acid/base reactions) between reacting
ions, molecules, or atoms. In other reactions, chemical bonds are broken by heat or
light to form very reactive radicals with electrons ready to form new bonds. Radical
reactions control many processes such as the ozone and greenhouse gases in the
atmosphere, burning and processing of fossil fuels, formation of polymers, and explosions.
Teacher Materials
Learning Sequence Item:
960
Acids, Bases and Indicators
March 1996
Adapted by: Patsy Janda and George Miller
Oxidation/Reduction, Acid/Base, and Radical Reactions. Students should mix acid and base solutions back and
forth to observe that one neutralizes the properties of the other. They should also observe the color changes of some
common indicators and observe what occurs when an acid or base is added to a water solution. (Chemistry, A Framework
for High School Science Education, p. 68.)
Contents
Matrix
Suggested Sequence of Events
Lab Activities
1. Acid-Base Indicators
2. Using the Best Indicator
3. The Gardener's Chemistry
4. Voice-Activated Chemical Reactions
5. Neutralizing Acids
Assessment
1. Indicators of Acid-Base
2. Neutral Solutions
3. How Acid Is It?
This micro-unit was adapted by Patsy Janda (University H.S., Irvine), and
George Miller (University
3 of California, Irvine)
960
Oxidation/Reduction, Acid/Base, and Radical Reactions. Students should mix acid and base
solutions back and forth to observe that one neutralizes the properties of the other. They should also
observe the color changes of some common indicators and observe what occurs when an acid or base
is added to a water solution. (Chemistry, A Framework for High School Science Education, p. 68.)
Learning Sequence
Science as Inquiry
Science and Technology
Science in Personal
and Social Perspectives
Acid-Base Indicators
Activity 1
How Acid Is It?
Assessment 3
pH and Hair
Reading 2
Using the Best Indicator
Activity 2
Swimming Pool Chemistry
Reading 1
Antacids
Reading 3
The Gardener's Chemistry
Activity 3
Voice-Activated Chemical
Reactions
Activity 4
Neutralizing Acids
Activity 5
Indicators of Acid-Base
Assessment 1
Neutral Solutions
Assessment 2
How Acid Is It?
Assessment 3
4
History and Nature
of Science
How Acid Is It?
Assessment 3
Suggested Sequence of Events
Event #1
Lab Activity
1. Acid-Base Indicators (20 minutes)
Event #2
Lab Activity
2. Using the Best Indicator (30 minutes)
Event #3
Lab Activity
3. The Gardener's Chemistry (20 minutes)
Alternative or Additional Activity:
4. Voice-Activated Chemical Reactions (Demonstration) (10 minutes)
Event #4
Lab Activity
5. Neutralizing Acids
Event #5
Readings from Science as Inquiry, Science and Technology, Science in
Personal and Social Perspectives, and History and Nature of Science
Students should select two from the following list:
Reading 1
Reading 2
Reading 3
Swimming Pool Chemistry
pH and Hair
Antacids
The above readings can be found in the student version of this publication.
Assessment items can be found at the back of this volume.
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Assessment Recommendations
This teacher materials packet contains a few items suggested for classroom assessment. Often, three
types of items are included. Some have been tested and reviewed, but not all.
1. Multiple choice questions accompanied by short essays, called justification, that allow teachers to
find out if students really understand their selections on the multiple choice.
2. Open-ended questions asking for essay responses.
3. Suggestions for performance tasks, usually including laboratory work, questions to be answered,
data to be graphed and processed, and inferences to be made. Some tasks include proposals for
student design of such tasks. These may sometimes closely resemble a good laboratory task, since
the best types of laboratories are assessing student skills and performance at all times. Special
assessment tasks will not be needed if measures such as questions, tabulations, graphs, calculations,
etc., are incorporated into regular lab activities.
Teachers are encouraged to make changes in these items to suit their own classroom situations and to
develop further items of their own, hopefully finding inspiration in the models we have provided. We
hope you may consider adding your best items to our pool. We also will be very pleased to hear of
proposed revisions to our items when you think they are needed.
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Activity 1
Teacher Sheet
Science as Inquiry
Acid-Base Indicators
How does an indicator distinguish acids and bases?
Materials:
2 beakers (500 mL)
graduated cylinder (l00 mL)
dropper
stirrer
water
universal indicator solution
dilute sodium hydroxide solution (NaOH)
small piece of crushed dry ice to fit inside the beaker
Procedure:
Have students label the beakers A and B and place 100 mL of water in beaker A. They should add 10
drops of universal indicator solution to beaker A, and then add, dropwise, dilute NaOH solution until the
color changes to purple, stirring the solution between drops.
Students then fill beaker B with crushed dry ice to the 100 mL mark. They should pour the solution
from beaker A over the crushed ice and carefully observe a color change.
Have students record the order of color changes and predict what will happen when the solution is
poured back into beaker A. Usually there is a small amount of NaOH solution left in beaker A to return
the color to blue or purple.
The experiment should be repeated by adding NaOH to the solution returned to beaker A until it is a
purple color. Students then pour the solution into beaker B and observe the change in color as the dry ice
melts. Have them predict the contents of the bubbles rising from the dried ice.
Background:
This activity shows how indicators change color when reacting with an acid or a base. The color
chart on the bottle of universal indicator shows the range of colors when added to solutions with different pH values. In this activity students start with a basic solution of sodium hydroxide as indicated by the
purple/violet color when the universal indicator is added.
When the solution is poured over the dry ice the water reacts with solid CO2 to produce an acidic
solution. The student should observe the indicator changing color to blue, then to green, yellow, orange,
and finally to red as the acidity of the solution increases.
The indicator color is related to the pH of the solution. The more acidic the solution the lower
the pH value.
purple—-pH 9 basic
blue——pH 8 basic
green—–pH 7 neutral
yellow—pH 6 acidic
orange—pH 5 acidic
red——–pH 4 acidic
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Activity 1
Further Variations:
Students can use the universal indicator solution to determine the acidity, or pH, of various household products. They should find soda, vinegar and lemon juice to be acidic, and milk, the juice of a green
pepper, and most cleaning products to be basic.
Students may be asked to take this investigation further by determining how much NaOH is needed
to neutralize an acidic solution or by turning the solution to a pH of 6 (yellow color). Conversely,
students can determine how much NaoH is required to neutralize a basic solution.
Adapted from Summerlin, L.R. and Ealy, J.L. Chemical Demonstrations, Volume I . Washington, D.C.:
American Chemical Society, 1988.
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Activity 2
Teacher Sheet
Science as Inquiry
Using the Best Indicator for pH Determination
Do indicators have specific pH ranges?
Materials:
8 test tubes or 8 reaction plates
test tube rack
water
thymolphthalein (in a dropper bottle)
phenolphthalein (in a dropper bottle)
phenol red (in a dropper bottle)
bromthymol blue (in a dropper bottle)
aqueous ammonia 1 M (or use 1% household ammonia solution)
effervescent tablet (i.e., antacid tablet)
Procedure:
Have students label eight test tubes (or label the wells in a reaction plate) 1A, 1B, 2A, 2B, 3A, 3B,
4A, and 4B, and place 5 mL of water into each tube (10 drops in each well). They should add two drops
of thymolphthalein to test tubes 1A and 1B (or one drop in wells 1A and 1B); two drops of phenolphthalein to test tubes 2A and 2B (one drop in wells 2A and 2B); two drops of phenol red to test tubes 3A and
3B (one drop to wells 3A and 3B); and two drops of bromthymol blue to test tubes 4A and 4B (one drop
to wells 4A and 4B).
Students then add two drops of ammonia to each test tube (one drop to each well), making sure the
thymolphthalein turns blue: if not they should add more drops of ammonia.
Breaking the effervescent tablet into small pieces, they should add one piece to test tube A (well) of
each pair and watch for a color change as the effervescent tablet dissolves. Have them compare the color
in each test tube A (well A) with the corresponding test tube B (well B).
Background:
This is a good example of the specificity of indicators for pH. Each of the indicators used in this
experiment changes color at a specific pH. Students begin the experiment with four pairs of test tubes or
wells, each with an alkaline, ammonia solution. When the effervescent tablet is added to the solution the
CO2 released causes the solution to become acidic. The color will change when the solution reaches a
specific pH for the indicator. If all the effervescent tablets are added at the same time, the test tubes will
change color in sequence as the pH decreases during the release of CO2.
Indicator
thymolphthalein
phenolphthalein
phenol red
bromthymol blue
Initial color
blue
pink
red
blue
Changes to
colorless
colorless
yellow
yellow
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pH range
10.6–9.4
10.0–8.2
8.0–6.6
7.6–6.0
960
Activity 2
The change in pH is a result of the reaction in which hydrogen ions are released into the solution as
the carbon dioxide dissolves.
CO2 + H2O ♦ H2CO3 ♦ H+ + HCO3–
This experiment can also be done as a demonstration with larger amounts of solutions and dry ice as
a replacement for the effervescent tablets.
Further Variations:
Discuss with the students what causes the decrease in pH. They may suggest additional experiments
that would return the indicator to its initial color. Discuss why bromthymol blue would be the preferred
indicator to measure the pH of blood, which has a normal pH of 7.4.
Adapted from Summerlin, L.R. and Ealy, J.L. Chemical Demonstrations, Volume I. Washington, D.C.:
American Chemical Society, 1988.
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Activity 3
Teacher Sheet
Science in Personal and
Social Perspectives
The Gardener’s Chemistry
How and why are soil samples tested for acidity?
Materials:
4 different soil samples
water (boiled and then allowed to cool)
wide-range pH paper (range between pH 2 and pH 8 is preferred)
four 200 mL beakers
filter paper
graduated cylinder (100 mL)
newspaper or paper towels
Procedure:
Have students label the beakers 1, 2, 3, and 4, making sure the beakers are dry. They should place a
strip of pH paper on the bottom of each and cover the pH paper with a piece of filter paper. They then
loosely fill each beaker with a different soil sample to the 100 mL mark.
Students then pour approximately 100 mL of preboiled water on the soil. The water should diffuse
through the soil sample and filter paper, moistening the pH paper, but not soaking it. They then turn the
beaker over onto a piece of newspaper or paper towel and observe the change in color of the pH indicator paper.
Have them repeat this procedure for the other soil samples.
To be sure the change in color is due to the soil and not the water, students should place a piece of
pH paper in the water and observe. The pH of this water control sample should be neutral, with a pH of
7.0.
Background:
This activity allows students to see how pH testing can be used outside the classroom. Soil pH is an
important consideration for plant growers.
Acidic soil allows iron and other nutrients to dissolve in water and therefore become available for
absorption by roots. If the soil is too acidic these nutrients form insoluble carbonates or hydroxides and
cannot be absorbed. Too much acid, however, may cause these nutrients to dissolve so well that they are
carried away or leach too deep for the roots to reach.
In this activity the water is preboiled to remove carbon dioxide, which can make the water acidic.
Distilled water should be used if the water is not neutral, pH 7.0.
Farmers and gardeners adjust the pH of their soil depending on the types of plants they want to grow.
Plants that prefer basic soil (pH 7.5–8.5) include beans, beets, lettuce, peas, cucumbers, carnations, and
cantaloupes. Plants that prefer acidic soil (pH 4-6) include raspberries, blueberries, peanuts, citrus trees,
azaleas and marigolds. If the soil is too acidic the pH can be raised by adding limestone or wood ashes to
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Activity 3
the soil. If the soil is too basic the pH can be lowered by adding grass clippings, pine needles, or decaying leaves. Soil near cement sidewalks or driveways is often basic due to the limestone leaching from the
cement. Soil collected from a wooded area containing a lot of mushrooms is often acidic, due to the
acidic biproducts from decomposition.
Further Variations:
Use probing questions regarding the use of the water control sample in the experiment. Ask students
how boiling the water can change it from an acidic to a neutral pH.
Students can bring in soil samples from their gardens or school grounds, as well as soil samples from
indoor plants. They may wish to keep a journal of the types of plants grown in or near the area the soil
was collected.
Students could hypothesize how to create a soil sample with a specific pH by mixing potting soil,
peat moss, wood ashes, and decaying organic material and then testing their hypothesis.
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Activity 4
an alternate/extension activity for Event 3
Teacher Sheet
Science as Inquiry
Voice-Activated Chemical Reactions
Is the breath acidic?
Materials:
two 500 mL Erlenmeyer flasks with stoppers
250 mL 95% ethyl alcohol
thymolphthalein indicator
phenol red
dilute sodium hydroxide solution (1 M NaOH)
Procedure:
Prepare the flasks before class by adding five–six drops of thymolphthalein indicator to 250 mL of
95% ethyl alcohol in one flask. Add dilute NaOH dropwise until the solution just turns blue. In the
second flask add one–two drops of phenol red solution to 250 mL of 95% ethyl alcohol. Add one drop of
dilute NaOH. The solution should be red. Keep both flasks stoppered until class begins .
You may want to preface this activity by suggesting that the solution(s) will undergo a chemical
reaction (i.e., color change) with the right voice. Ask for a volunteer from the class. The student should
wear safety goggles and speak a few words into the flask and then quickly restopper it. Swirl the flask
and observe. Ask for another volunteer to repeat the task.
Continue until the solution changes color. Return the solution to the original color by adding
dropwise dilute NaOH. Be sure to not add too much NaOH; it should just barely turn color.
Background:
This is a good demonstration that CO2 dissolved in water is acidic. Thymolphthalein is blue at pH
10.6 but is colorless at pH 9.4. Phenol red is red at pH 8.0 but is yellow at pH 6.0. As students speak into
the flask the carbon dioxide exhaled will dissolve in the liquid solution. When enough CO2 is dissolved
to change the pH to the appropriate level the students will observe a color change. The thymolphthalein
solution will reach the indicator pH with fewer students than will the phenol red solution. Be careful not
to start the solutions at too basic a pH. When preparing the solutions add just barely enough NaOH to get
to the desired initial color.
Use safety precautions. Ethyl alcohol is flammable and students should wear safety goggles.
Swirling the flask between students may speed the reaction. You can get through more student
volunteers if you do not swirl after each student. Keep the solutions stoppered to prevent atmospheric
CO2 from changing the colors.
The chemical reaction involved in this activity is:
CO2 + H20 ♦ H 2CO3 ∩ H+ + HCO3–
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Activity 4
Further Variations:
Ask students to suggest what is causing the chemical change and why the color change did not occur
with the first student.
Adapted from Summerlin, L.R. and Ealy, J.L. Chemical Demonstrations, Volume I. Washington, D.C.:
American Chemical Society, 1988.
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Activity 5
Science as Inquiry
Neutralizing Acids
How do antacids work to neutralize the acids
produced in the stomach for digestion?
Materials:
antacid tablet or 1 teaspoon baking soda
white vinegar
phenol red indicator
water
beaker (100 mL)
dropper
stirrer
Procedure:
Students place 100 mL of water into the beaker, add two drops of vinegar to the water, and mix well.
They then add two–five drops of phenol red indicator to turn the solution to a yellow color. They drop
the antacid tablet into the solution and observe for a color change.
Background:
This activity demonstrates that antacid tablets change the chemical nature of an acid. Antacid tablets
usually contain a carbonate, which reacts with the hydrogen ions in the acidic solution to produce carbon
dioxide gas.
H+
+ HCO3– ♦ CO2 + H2O
Phenol red indicator has a color range of red to yellow with a pH range of 8.0–6.6. As the hydrogen
ion concentration in the vinegar solution is reduced, the pH value will rise, causing the indicator to
change from red to yellow.
How effective an antacid is at neutralizing stomach acid is related to both the amount of acid it will
neutralize and the speed of the reaction. A more gradual, rather than fast, reaction rate is desirable since
it is less likely to induce production of additional hydrochloric acid. The concentration of hydrochloric
acid in the stomach varies from 0.0% to .5% of the gastric juice. Antacids are used to neutralize excessive acid production.
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Activity 5
Further Variations:
This activity can be used with either baking soda or antacid tablets. Students can expand on this
activity by designing an experiment to explore how temperature affects the rate of the reaction (heat will
speed up the reaction rate) or to find the optimum mass of antacid required to neutralize a given amount
of vinegar-water solution.
Phenol red indicator can be substituted with bromthymol blue or cabbage juice indicator. To make
cabbage juice indicator, slowly boil a red cabbage leaf in about 1/2 cup of water until the water turns a
dark color. The red color will turn yellow in an acidic solution.
Adapted from Chem Matters Volume 1(2), 1983.
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Assessment 1
Science as Inquiry
Indicators of Acid-Base
Item:
Ten drops of phenolphthalein indicator are added to separate samples of lemon juice, water, and household ammonia.
A. The lemon juice turns pink.
B. The ammonia and lemon juice turn pink.
C. The water turns pink.
D. The ammonia solution turns pink.
Justification:
What effect do acids and bases have on phenolphthalein?
Answer:
D. In the presence of acids, phenolphthalein is colorless, and in the presence of bases it is pink.
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Assessment 2
Science as Inquiry
Neutral Solutions
Item:
Solution X is made by adding a solution of vinegar to a solution of ammonia until the initial concentrations of the ammonia and vinegar in the mixture are equal. This solution has five drops of universal
indicator added.
Solution Y is made in a similar way, except from solutions of hydrochloric acid and sodium hydroxide.
Five drops of universal indicator are added to solution B.
It is expected that:
A.
B.
C.
D.
The colors of the two solutions will be the same.
One solution will be red, the other blue.
One solution will be green, the other yellow.
The colors cannot be predicted, as different acids react differently with universal indicator.
Answer:
A. Since both solutions have reached a neutral (equivalence) point, the colors should be nearly the same.
Students who have studied advanced chemistry may miss this because they may think that a weak acid,
weak base system always has neutralization distinctly far from pH = 7, since most of the examples
included in books are that way.
Background:
The weak acid, weak base pair will neutralize at pH = 7 effectively since the ionization constants of
ammonia and acetic acid are nearly the same. Another way to state this is that dissolving the salt ammonium acetate in water gives a nearly neutral (pH = 7) solution.
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Assessment 3
Science as Inquiry/
Science and Technology/
History and Nature of Science
How Acid Is It?
Performance Task Assessment
Bases neutralize acids. It is possible to use a neutralization reaction to determine the amount of acid in a
particular solution. In this task students will determine the acid and compare the acid in different carbonated beverages. Suggested are 7-Up, Sprite, Tonic, Club Soda, and seltzers. The acid in the carbonated
beverage will be neutralized with dilute sodium hydroxide. (If the school has CEPUP/SEPUP kits, the
dilute ammonia can be substituted for the sodium hydroxide, and universal indicator can be used.)
Materials:
test tubes
one dropper for each test tube
graduated cylinder
4 different clear, colorless, carbonated beverages
phenolphthalein indicator (1% in ethanol)
dilute sodium hydroxide solution (about 0.1 M)
[Alternative: well trays and marked transfer (beral) pipettes]
Student Procedure:
Prepare a data table to display your results. Measure equal amounts of each of four carbonated
beverages into test tubes (or wells). Add two drops of indicator to each of the beverage samples.
Add the base solution drop by drop to the beverage until a permanent faint pink color indicates that
the acid is neutralized. If you are using universal indicator, pick the neutral color on the chart at which to
stop the addition. Stir or swirl after each drop.
Record the number of drops of base used to neutralize the carbonated beverage in each case. With
universal indicator you can plot the pH against the number of drops added.
Questions:
1. Did each beverage require the same amount of base? If not, which beverage is more acidic?
2. Phenolphthalein changes from a colorless liquid to a pink one at a pH of 8. Why was the indicator
colorless in the beverage and pink after sodium hydroxide was added?
(Alternative question: Why did the universal indicator change color as the base was added? What is
the pH change as indicated on the color scale? Comment on the shape of your graph.)
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Assessment 3
3. If some distilled water were added to base solution, would the number of drops needed to neutralize
the carbonated beverage sample increase, decrease, or remain the same? Explain your answer?
4. Arnold Beckman invented an instrument called a pH meter to measure the changes of acidity in
orange juice. pH meters are quite expensive, but they are used extensively by the juice industry. Why
do you think they could not have used the much cheaper method that you just used?
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