SOTM LAB: B 2M 11/23/99
I. TEACHER NOTES & GUIDELINES
TITLE OF LAB: UNDERSTANDING pH (B2)
DEVELOPERS OF THE LAB: Sally Cross JD867, Angela Flanagan JD883, Patrick
Hancock JD892, Fran Kallman JD724, David Moss JD594, Sibylle Tulve JD746, Christine
Zamenick JD589, SOTM Staff.
OVERVIEW OF THE LAB:
Though this activity does have students utilize conventional test papers and indicators for
acids and bases, the focus is on the utilization of the computer and an electronic pH probe
to obtain more accurate and precise pH readings. The teacher provides the solutions to be
tested, and leads the students into their own inquiries about acids and bases. Again, the
emphasis will be on the use of the electronic equipment to gather precise pH readings.
From this activity it is anticipated that the role of acids and bases in the ecosystem will be
investigated, and further activities and inquiries will evolve.
The teacher background information presented here supports the topics of environmental
science, the water cycle, and pollution. However, the lab activity and inquiry themselves
are also appropriate when studying digestion, chemistry, or types of solutions.
1. Solutions are not to be tasted, touched, or smelled.
2. No solutions are to be mixed without the instructor’s permission. (Although the
solutions used in this lab are generally harmless, it must be stressed to students that
indescriminate mixing of chemicals may result in injury.)
3. Safety goggles are to be worn.
4. Glassware safety protocol should be followed.
5. Electrical safety protocol should be followed.
6. The pH sensor probe is to be rinsed with distilled water and dried with a kimwipe
before and after each sampling.
A. SCIENTIFIC VIEWPOINT:
*an acid is a substance that increases the hydrogen ion concentration in a
*a base is a substance that decreases the hydrogen ion concentration in a
*pH scale is a measure of the hydrogen ion concentration ranging in value from
*a solution of pH 3 is not twice as acidic as a solution with pH 6, but a thousand
times more acidic (each whole # change in pH value is equal to a factor of 10)
*buffers are substances that minimize the change of pH when adding an acid
or a base to a substance
*most biological fluids are within the range pH 6 to pH 8 (there are a few
exceptions including the human stomach’s digestive juice with a pH of about 1.5)
*human blood normally maintains a pH of 7.4 due to the presence of buffers; a
person cannot survive for more than a few minutes if the blood pH drops to 7.0
or rises to 7.8
*normal, uncontaminated rain has a pH of 5.6 because of CO2 which combines
with water to form carbonic acid
*Acid precipitation refers to rain, snow, or fog that is more acidic than pH 5.6; this
is a result of sulfur oxides and nitrogen oxides (released from the combustion
of fossil fuels by factories and automobiles) combining with water in the atmosphere
*acid precipitation is harming both terrestrial and freshwater ecosystems
*the pH of soil affects the solubility of minerals; some mineral nutrients are washed
out of the topsoil while other minerals (such as aluminum) reach toxic concentra-
tions; both have a negative impact on the plant life
*the pH of lakes and ponds has been lowered by the leaching of certain minerals
from the soil by acid rain, having an adverse affect on many species of fish,
amphibians, and aquatic invertebrates; acidity may kill water plants, deform
fish, and prevent fish eggs from developing; some lakes at higher elevations in the
Adirondacks have a pH less than 5.0 and fish have completely disappeared
*acid precipitation can be reduced through industrial controls and antipollution
devices; there is some evidence that sulfur oxide emissions have decreased by
as much as 30% since 1985
B. COMMON MISCONCEPTIONS:
Misconceptions about acids and bases will be ascertained by pre-lab brainstorming,
small group discussions, and class discussions identified and described within.
At the conclusion of this lab activity, students will be able to:
1. identify acids and bases based on their pH
2. use indicators to identify acids and bases
3. work with computers to take pH measurements
4. demonstrate the neutralization of an acid and a base
5. understand the relationship between acids, bases, and the pH scale
6. design and perform a simple neutralization reaction
PROVIDED BY SOTM:
laptop computers kimwipes
computer interfaces magnetic stirrers/ hot plate (and stir bars)
pH probes possibly extension cords/ power strips
buffer solutions of pH 4, 7, and 10 wash bottles
surge protectors optional: magnetic stir plates spinbars
pH test papers
red litmus paper
blue litmus paper
wash bottles with distilled water (1 for each station)
collection vessel for waste water (1 for each station)
50 mL beakers (one for each solution X how many stations to be set up)
100 mL beaker with distilled water (1 for each station)
100 mL graduated cylinders (1 for each station)
medicine droppers (1 for each station)
electrical outlets (each lab station requires 2 outlets)
unknown solutions to be tested (acids= lemon juice, orange juice, tomato juice, vinegar,
club soda, pickle juice, sauerkraut juice, rainwater; bases= lime water, liquid soap, liquid
detergent, shampoo, milk of magnesia, baking soda solution)
1. Prepare acid/ base solutions (quantity to be determined by the teacher).
2. Label each 50 mL beaker with the name of the acid/base solution it will contain, then fill each
beaker to the desired level.
3. Set up each lab station with the following:
-test papers of all types
-50 mL beakers of the solutions to be tested
-100 mL beaker of distilled water
-one wash bottle of distilled water
-collection vessel for waste water
-electric power supply with 2 outlets
4. Begin soaking the pH probes in the beaker of distilled water. Preferably overnight.
5. Refer to the General Procedure for Starting Science Workshop with Library.
6. For Item 4 select “biology”
7. For Item 5 select “b04_buff.sws
8. Close the “Experiment Notes” window
9. Click on Display menu and on New Digits
10. On the B04 line of the setup window, click on the box next to the X to view the interface
11. Double click on the box with pH in it.
12. Using a sample of buffer at pH 10 for high value and one of pH 4 for low value, set the high and
low value readings. This is accomplished by inserting the probe into the solution, clicking the
“Read” button, and typing in the proper pH value in the first box on the line. Remember to rinse
off the probe between all solutions and wipe off the probe with a Kimwipe.
13. When finished, click on “OK”. All probes in the classroom should read the same values, if
the procedure was followed correctly.
EXERCISE TO ELICIT STUDENTS’ PRIOR KNOWLEDGE AND
This is designed to elicit students’ prior knowledge and misconceptions regarding acids, bases,
Divide class into groups of three or four students. In a five to seven minute time frame, have the
students brainstorm any knowledge and ideas they may have concerning acids, bases, and/or pH.
One student will record the group’s information. No information that is offered is discounted.
After this period of time, teacher leads a class discussion by asking each small group, in turn, to
give one fact from its list. From these offerings, the teacher constructs a class list (either on the
board or, ideally, on large sheets of paper) and continues in this manner until no group can offer
any additional facts or input.
From this master list, teacher will guide discussion about any thoughts that students have
expressed about acids, bases, and pH. Teacher may want students to copy down those ideas
shared through this class discussion in their notebooks. The master list will also be kept
available for future reference.
DISCUSSION OF PRECONCEPTIONS:
Any preconceptions that students bring forth during this teacher-led discussion will become the
basis for the student-generated inquiry labs/experiments/activities that will follow. This pre-lab
activity will allow students to formulate and share ideas that will be supported or refuted by their
III. EXPLORATION OF SCIENTIFIC PRINCIPLE &
INTRODUCTION OF EXPERIMENTAL
The purpose of this activity is to introduce students to the use of conventional pH indicators and
scientific instrumentation using computer-interfaced technology to show enhanced methods of
obtaining similar information. It will allow students to see similarities and differences in
obtaining scientific data and it will provide some practical knowledge regarding characteristics
of acids and bases.
How can the pH value of substances be determined?
EXPERIMENT AND TECHNICAL OPERATION OF EQUIPMENT:
This activity will consist of several parts. In Part I, students will familiarize
themselves with the equipment and the types of data they will be getting as they test acids and
bases and determine pH. They will be given substances whose pH values are known so that they
can learn what types of results to expect. In Part II, they will use the information gained in Part I
to guide them as to what they can expect for their results. In Part III, they will be given an acid
and be asked to neutralize it to ascertain how a neutral solution can be obtained.
Part I. Finding the pH of “known” solutions
Materials (local): pH paper, red litmus paper, blue litmus paper, phenolphthalein
paper, wash bottle with distilled water, container for used water, 50 mL beakers
for each solution, paper towels
Materials from SOTM: laptop computer with pH sensor, buffer solutions of
known pH value (one acid, one base, one neutral), kimwipes
1. Find the pH of the solution marked “acid” by using each of the indicators and the pH
sensor. Record the information in the chart. For the red and blue litmus paper and the
phenolphthalein, record the color. For the pH paper and the pH sensor, record the
numerical value for the pH. For the pH sensor, give the pH reading accurate to one
2. Repeat step 1 for the solution marked “base.”
3. Repeat step 1 for the solution marked “neutral.”
Substance pH paper Red litmus Blue litmus Phenolphthalein pH sensor
QUESTIONS: Base your answers to the following questions on the data in your table.
1. What results do you expect from your indicators for a neutral solution?
2. What results do you expect from an acidic solution?
3. What results do you expect from a basic solution?
Part II. Finding the pH of “unknown” solutions.
Materials (local): (solutions whose pH values are unknown may include the following):
lemon juice, orange juice, tomato juice, vinegar, club soda, pickle juice, sauerkraut juice,
rainwater, lime water, liquid soap, liquid detergent, milk of magnesia, baking soda
solution, shampoo, pH paper, red litmus paper, blue litmus paper, phenolphthalein paper,
50 mL beaker for each unknown solution, wash bottle with distilled water, container for
waste water, paper towels
Materials from SOTM: laptop computer with pH sensor, kimwipes,
1. Following the same procedure used for Part I (Finding the pH of known
solutions), record the results for all of the unknown solutions.
2. List each of the solutions whose pH values are unknown on the chart below.
Be sure to record the pH values for the sensor readings to one decimal point.
Substance pH paper Red litmus Blue litmus Phenolphthalein pH sensor
3. Based on the pH you recorded for each solution that you tested, write the name of
each substance on the correct location on the pH scale below. Make a mark where the
solution would be located based on the results you obtained and then label that mark.
Part III. Neutralizing an acid.
Materials (local): dilute (1:30) vinegar, baking soda solution (50 mL), 100 mL
beaker, graduated cylinder, medicine dropper, paper towels
Materials from SOTM: laptop computer with pH sensor, magnetic stirrer,
1. Place 20 mL of the dilute vinegar solution in the 100 mL beaker.
2. Using the laptop computer with the pH sensor, find the pH of the dilute
Record this value on the chart.
3. Place the beaker containing the vinegar on the magnetic stirrer and gently put
the stirring bar. Turn on the stirrer so it is slowly stirring the vinegar.
4. While the vinegar is being stirred, add 20 drops of the baking soda solution to
the vinegar with the medicine dropper. Note any changes in the pH value.
Record this pH value on the chart. (Make sure the baking soda stays in
suspension by stirring it frequently.)
5. Continue in this manner until the pH of the vinegar solution becomes 7.0
(neutral). Record all information on the chart.
Number of drops added pH value
0 (starting pH)
6.Use the information from the previous chart to graph the changes in the pH value as
you conducted your activity.
pH/ 20 40 60 80 100 120 140 160 180 200 220
1. What is neutralization?
2. What type of solution must be added to an acid in order to neutralize it?
3. How do you suppose a base is neutralized?
IV. ELABORATION OF SCIENTIFIC PRINCIPLE:
INQUIRY-BASED STUDENT INVESTIGATION
By now each of you has gained knowledge about acids, bases, and pH. If you think back
to the first day and the list of “facts” gathered from the class, you will be able to analyze
each statement made as a student more educated about acids, bases, and pH.
But there is still much to learn. What would you like to learn about acids, bases, and pH?
You will be working independently researching and experimenting on a topic of your
choosing. What will it be? Give it some thought, then state your idea in the form of a
Problem Statement: _________________________________________________________
HYPOTHESIS OR PREDICTION:
1. What will you need to research on the computer or in the library about your topic?
2. You are required to incorporate an experiment to test or support your idea, or to
gather information about your topic. You are to use the materials used in the
lab, or you may be bringing in other supplies from home (with teacher’s permission).
How will you incorporate an experiment into your investigation? What will you test?
Give some thought, then identify your ideas below.
3. Check off which of the following you will be using in your experiment:
____laptop computer with Science Workshop program
____computer interface and pH probe
____pH test paper
____red/ blue litmus paper STOP... SUBMIT FOR TEACHER SIGNATURE
EXPERIMENTAL DESIGN: Include in your procedure all steps, types of data to be
collected, and graphs, charts and tables to be created.
APPROVAL AT CHECKPOINTS
STUDENT EXPERIMENT ON ACIDS, BASES, pH
PURPOSE OF THE EXPERIMENT STEPS IN PERFORMING THE EXPERIMENT
EXPECTATIONS OR PREDICTIONS
TYPES OF DATA TO BE COLLECTED
CHARTS, TABLES, GRAPHS TO BE CREATED
PLAN FOR DATA COLLECTION & ANALYSIS
Use the space below to draw a final copy of any data table, chart, or graph that you
use to represent the data collected during your experiment, or as a result of your
CONDUCTING THE EXPERIMENT
While you are conducting the experiment, the teacher will monitor your work and initial
the following items.
____student gathered all materials before beginning the experiment
____student measured and labeled all solutions to be used
____student handles materials and equipment in a responsible manner
____student follows safety protocol for glassware, unknown chemicals, and electrical power
____student is able to explain and describe his procedure as the experiment progresses
____student records observations and data as the experiment progresses
____student asks for assistance from teacher if needed
____student ends experiment at the appropriate time and in the appropriate manner
____student returns materials and supplies to their proper place
____student returns laptop computer, interface, and pH probe to the original condition
____student cleans up materials used
____student cleans up work station
ANALYSIS OF DATA
In the space below, provide a written analysis of the data collected during your
experiment. Refer back to your data table, graph, etc. Take a few minutes to review
what you recorded and remember your experiment. Then begin your written analysis.
Remember to express yourself in a way that demonstrates your understanding. Do not
assume the reader understands what you mean. You will present your analysis to the
class at a future date.
DISCUSSION OF RESULTS
Visit with 2 other students in your class. During your visit you are to discuss
experiment and your experiment in the following way:
-briefly describe what each of you was investigating about acids, bases, or pH
-identify what you hoped to learn by completing your experiment
-identify whether or not you did get the information you were after, and were
the results what you expected?
-discuss together whether your results are something that can apply to all similar
acids or bases, or whether your results are unique to the substances you used
-offer support and words of encouragement to your partners
POST-LAB SURVEY OF STUDENT’S CONCEPTIONS
Re-form into your original 3 person group to discuss the original class list about acids, bases, and
pH. Take 5 minutes to revisit what was written and come to a group consensus
about the accuracy of each statement. Identify what part or parts of each sentence are true
or false. Select one person from your group to participate in the class discussion that will
Complete each sentence with a word, phrase, or number.
1. Acids have a pH of _______ to _______.
2. Strong acids have a pH close to ______.
3. Weak acids have a pH close to ______.
4. Bases have a pH of ______ to ______.
5. Strong bases have a pH close to ______.
6. Weak bases have a pH close to ______.
7. A neutral solution has a pH of ______.
8. To neutralize an acid ___________________________________________.
9. To neutralize a base ____________________________________________.
10. As a base is added to an acid, the pH number ________________________.
THE GUEST SPEAKER
You are a visiting guest speaker at a school of fish in a freshwater lake in upstate
New York. The young fish are about to begin a unit on acid rain and how it is
changing their environment. You, as the expert, are at the school to explain to
the young fish what acid rain is, where it comes from, how they can recognize it,
what changes have taken place in their environment since you were a young fish,
what changes they can expect to see in the future if steps are not taken to reduce
the current acid rain problem, and so on. Since these are young fish that might
be easily frightened, be sure to conclude on a positive note for them to leave
feeling hopeful. What steps are being taken by humans to reduce or solve this
problem of acid rain.
Requirements: 5 minute presentation to the class, in the role of the guest speaker
Creation of 2 visual aids such as a poster, overhead transparency,
or model. These are to support your presentation, but are
to be designed for young fish, so design accordingly.
5 Excellent Presentation: Presentation explains the meaning of
rain, where it comes from, how students can recognize it, what
changes have occured in their environment, what future changes might
occur, etc. A “happy ending” is provided to reduce young fish stress
syndrome. 2 visual aids were presented: age appropriate, educational,
accurate, and neat.
4 Good Presentation: Presentation is age appropriate and includes
2 visual aids, but student fails to address 1 or 2 key points that
3 Adequate Presentation: Presentation is age appropriate, but is lacking
2 or more key points, and visual aids need refinement.
2 Inadequate Presentation: Presentation is not age appropriate; visual aids
are not age appropriate.
1 Presentation Gives False Information: Demonstrates a lack of under-
standing of acid rain and the impact on the environment. Visual aids
provide little information of value. Student does, however, get up in
front of peers.
0 Student absent/ Student Does Not Present
*This material is based upon work supported by the National Science Foundation under Grant No.
ES1 9618936. Any opinions, findings, and conclusions or recommendations expressed in this
material are those of the author(s) and do not necessarily reflect the views of the National Science