Acids & Bases Lab
Pre-Lab
1. What scale is most commonly used to measure alkalinity or acidity?
2. What are instruments using this scale actually measuring?
3. Draw a scale and indicate:
a. The values that are considered acidic, neutral, or alkaline.
b. What end of the scale is MOST acidic or MOST alkaline.
c. The direction of increase of H+ (Hydrogen) or H3O+ (Hydronium) ions in solution
d. The direction of increase of OH- (Hydroxide) ions in solution
4. Research where each of the chemicals/solutions listed as Unknowns in Part B falls in the scale.
5. Based on the scale you created explain why
a. Distilled water is considered neutral.
b. Adding HCl (Hydrochloric acid) will typically increase acidity
c. Adding NaOH (Sodium Hydroxide) will typically increase alkalinity
6. Explain what it means that this scale is logarithmic and to illustrate the point, demonstrate how many times stronger a 1 is than:
a. 2
b. 4
c. 7
Objective:
 Students will create and/or use various pH indicators that can be used to test unknown solutions to determine if they are an acid or a base.
 Students will understand the difference between acidity, alkalinity, and neutrality in terms of p.H scale
 Students will examine the role of buffers and neutralization reactions
 Students will perform/design experiments examining the effects of p.H on living system.
What is pH?
The terms acid and base describe chemical characteristics of many substances that we use daily. We use bases to make soaps and detergents,
for example. Almost all the foods we eat, from bread to coffee, are slightly acidic.
The pH scale is a measure of acidity. You can buy pH indicator paper from any biological or lab supply company, which can be used to give
you an accurate measurement of the acidic or basic quality of substances you want to test. You can also make your own pH indicator using red
cabbage juice, for example, to track the changing pH in your fermentation chamber.
Students will be testing the pH level of several different solutions using pH indicators. Pure water is said to be neutral, with a pH close to 7.0 at
25 °C (77 °F). Solutions with a pH less than 7 (at 25 °C (77 °F)) are said to be acidic and solutions with a pH greater than 7 (at 25 °C (77 °F))
are said to be basic or alkaline. A solution with a pH of 6 is 10 times more acidic than pH 7, but is 100 times more acidic than pH 8.
Detecting p.H.
A pH indicator is a chemical compound that is added in small amounts to a solution so that the pH (acidity or alkalinity) of the solution can be
determined easily. pH indicators are usually weak acids or bases themselves. They detect the presence of hydronium ions (H 3O+) or hydrogen
ions (H+).
A procedure known as titration can be used to determine the presence of an acid or base. Titration uses the reaction between an acid and a base
known as neutralization to determine the pH.
 A strong acid reacts with a strong base to form a neutral (pH=7) solution.
 A strong acid reacts with a weak base to form an acidic (pH<7) solution.
 A weak acid reacts with a strong base to form a basic (pH>7) solution.
Part A: Making Natural p.H. Indicators
Each group members should perform one of these options at home and bring it ready to class. If student wants teacher assistance in the
preparation, student is welcomed to make arrangement to stay after school prior to the due date.
Note: Group members should make enough indicator solution / paper to perform all parts of the experiment
Make sure to read to your designated procedure so that you know all that you will need to prepare your p.H. indicator before you start.
Beet Juice Indicator Solution #1
Wash and slice a fresh beet. Place about four slices of beet into a pan containing one cup of water. Heat until
boiling and continue boiling for about five minutes. Remove the beet slices and allow the red liquid to cool.
Store juice in dropper bottles. Beet juice is red in acidic solutions and blue in basic solutions. Beets
contain a pigment known as anthocyanin that will change from red to yellow somewhere between pH 11
and 12.
Phenolphthalein Indicator Solution #2
urchase any laxative that contains phenolphthalein. With the back of a spoon, mash four to six tablets in a
saucer. Pour the powder into a small cup. Add about ten milliliters of rubbing alcohol. Let this mixture stand
for fifteen minutes. Pour off the liquid and store in a dropper bottle. Phenolphthalein is purple in very basic
solutions and colorless in acidic solutions.
Turmeric Indicator Solution #3
Obtain a package of turmeric form the spice section of the grocery store. Add 1/4 teaspoon of
turmeric to four tablespoons of rubbing alcohol. Stir to mix. Store in dropper bottle. Turmeric
solution stays yellow in the presence of acids and changes to purple-brown in the presence of
bases. Turmeric solution can also be made into indicator paper (see Cabbage Paper). Dry turmeric
paper is bright yellow and changes to red in the presence of bases.
Red Cabbage Indicator #4
Note: Actual color might vary with cabbage used. It may be wise to perform a calibration procedure
where indicator liquid is tested against
Tear five leaves of red cabbage into small pieces. Place the cabbage pieces in a small pan. Add four
cups of hot water. Let the leaves soak for about half an hour until the water is a deep purple and
cooled to room temperature. Strain the liquid into a storage bottle. Cover and store in the
refrigerator. Red cabbage juice indicator is red in acid solutions, purple in neutral solutions, and
greenish-yellow in basic solutions. Red cabbage contains a pigment molecule called flavin (an
anthocyanin). This water-soluble pigment is also found in apple skin, plums, poppies, cornflowers,
and grapes. Red cabbage juice will function over a wide pH range, from as low as pH 1 up to pH
12.
Cabbage Indicator Paper (Optional):
Note: If you are performing part C-E and pH strip paper is not available, you will need this.
Pour one cup of cabbage indicator (above) into a bowl. Dip one or two coffee filters into the
indicator. Place the wet filter paper on a cookie sheet or flat pan. Continue to soak the paper until
saturated. Allow the paper to dry (this will take more time than your class time, so use it the next
day or for another activity). The paper will be pale blue. Cut the dry papers into strips about 1.25
by 7.5 centimeters (0.5 by 3 inches). Store the strips in a zip-lock plastic bag. Cabbage paper
Another way to use your pH paper is as a color-change paper. You can draw on pH paper using a
toothpick or cotton swab that has been dipped in an acid or base.
Part B. Testing p.H Indicators with Unknown Lab
CAUTION: Students will be working with chemicals that could cause injury. All students should review proper safety laboratory procedures
prior to this experiment. All care should be taken to avoid spills and contact with skin or eyes. This includes the use of safety goggles, aprons,
and gloves. If there are any contact accidents, students should use emergency wash stations to wash eyes and sinks to wash hands. In case of
full body exposure, there should be an emergency shower stations in the laboratory. Teacher should be immediately notified of any such
emergency. Spills should also be notified immediately and properly cleaned.
Materials: Test tube racks
Test tubes 10
Beakers (250ml) x # of Unknowns
Syringe (5ml) x 4
Possible Unknowns:
Ammonia
Apple Juice
Baking Soda Mix
Bleach
Syringe (10ml) x # of Unknowns
Marker
Masking Tape
Distilled Water
Hydrochloric Acid (0.1M)
Hydrogen Peroxide
Lemon Juice
Lime Juice
Milk
Milk of MagnesiaOrange
Juice
Watch glass or Petri dish or Tray
Sodium Hydroxide (0.1M)
Sprite / 7Up
Tap Water
Vinegar
Procedure
Unknown Preparation
1. Setup a station with several 250ml Beakers or cups labeled with letters (A-Z).
2. Fill each container with a different chemical or solution of known p.H. values
(See possible list above. Student should research the p.H. values of these items as part of their pre-lab activity)
3. Place 10ml syringes in front of each sample. These are to be used to collect samples from stock solutions into students working solutions
4. Each group receives 10 test tubes and test tube rack
Paper Indicators (Optional): These procedures are to be repeated for each type of pH. indicator used. All chemicals should be diluted before
being dispensed (as instructed by teacher) and test tubes should be thoroughly washed and dried between each test.
1. Make sure paper is cut into strips and place them on clean watch glass or petri dish
2. Label strips with unknown letters or tube numbers
3. Place a 1-2 drops of unknown solution to be tested directly on the paper that represents it
4. Repeat procedure until all unknowns are tested
ALTERNATIVE: Teacher may provide or students may bring their own pH. testing strips to add to this part of the experiment.
Liquid Indicators: These procedures are to be repeated for each type of pH. indicator used. All chemicals should be diluted before being
dispensed (as instructed by teacher) and test tubes should be thoroughly washed and dried between each test.
1. Using masking tape and marker, tubes should be labeled near the top with numbers 1-10
2. In similar fashion, each of the 4 syringes (5ml) to be used to dispense indicators should be labeled so it is clear to which indicator they
belong.
3. Using a 5ml syringe, add 2ml of indicator solution into each one of the test tubes.
4. Each group should approach sample station with test tube rack containing all 10 tubes labeled and with appropriate amount of
indicator placed
5. Teacher will assign each group a set of unknowns. Groups should keep track of which unknowns they are to be testing by indicating
their letters on the data table. Students should be careful to match unknown letters to test tube numbers listed on the data table.
6. Using the 10ml assigned to each sample (syringes will be located near the sample and should be returned there), students should
collect a 10ml sample of the unknown.
7. Measuring p.H.: (To be performed one test tube at a time):
a. Remove test tube to tested from the rack
b. Students should add unknown drop by drop to each of the test tubes containing indicator solutions.
c. Between drops, solution should be mixed by swirling the tube and/or by gently shaking or agitating tube (holding between index
and thumb of one hand and thumping with middle of another).
d. Students should continue to add unknown to test tubes until the color changes or the solution volume doubles.
e. Color changes (or lack of after doubling the volume) should noted in data table
Note: Though any color change after doubling the volume should be noted in the data table, a true color change is different from a
dilution of color (as it would happen if you were to add a lot of water to a homogenous deep blue solution  may become light
blue)
f. Return test tube to the rack and repeat procedures with all test tubes
8. After all test tubes have been tested, the contents should be properly disposed (follow teacher instructions) and tubes should be
washed and dried. Then, the procedure should be repeated with the next indicator solution until all indicator solutions are tested.
9. After all indicators have been tested, use charts and keys (See Part A) to estimate p.H. of unknowns
10. Based on original color of chemicals, p.H estimations, and background research as to the pH of unknowns bank make an educated
guess as to the nature of the unknowns and determine if they are an acidic (acid), alkaline (base), or neutral substance
ALTERNATIVE: If there are enough test tubes to give each group 40, all indicators can be tested at once. In such case, test tubes should
be labeled with unknown letter and indicators to be used. The number of indicators or unknowns can be reduced to save time and
materials. Another alternative is to use a testing tray with wells that could hold at least 5ml of samples. Alternatively, a smaller well tray
can be used with reduce indicator/sample volume to smaller amounts, such as 1ml (Use smaller syringes. More difficult to observe color
change)
Results
Original Color of Indicators:
Beet Juice
Phenolphthalein
Tumeric Solution
Cabbage Juice
Tumeric Paper
Cabbage Paper
Lab Data
Tube
#
Unknown
Letter
Guess
Beet
Juice
Original
Color
Tumeric Cabbage
Solution
Juice
Phenolphthalein
Tumeric
Paper
Cabbage
Paper
pH.
Paper
pH.
Estimate
Acid /
Base /
Neutral
1
2
3
4
5
6
7
8
9
10
pH Scale of Unknowns Based on Data
0
1
2
3
4
5
6
7
8
9
10
11
12
13
Analysis / Discussion:
1. Beet juice indicator solution will be red in a/an_______.
2. Beet juice indicator solution will be blue in a/an_________.
3. Cabbage indicator solution will turn what color in the presence of bases
4. Phenolphthalein indicator solution will turn what color in the presence of bases?
5. Phenolphthalein indicator solution will turn what color in the presence of acids?
6. Turmeric indicator solution stays yellow in the presence of acids and turns what color in the presence of bases?
7. What was the purpose of this activity?
8. While working in a lab, an unknown chemical spill occurs. Explain the process and observations you would use to determine if the chemical is neutral, acidic, or alkaline
9. Identify possible sources of errors in the procedures or performance of the lab:
14
Part C. Buffers & Neutralization Reactions
Background:
Scientists use something called the pH scale to measure how acidic or basic a liquid is. The scale goes from 0 to 14. Distilled water is neutral
and has a pH of 7. Acids are found between 0 and 7. Bases are from 7 to 14. Most of the liquids you find every day have a pH near 7. They are
either a little below or a little above that mark. When you start looking at the pH of chemicals, the numbers go to the extremes. Substances with
the highest pH (strong bases) and the lowest pH (strong acids) are very dangerous chemicals. Molecules that make up or are produced by living
organisms usually only function within a narrow pH range (near neutral) and a narrow temperature range (body temperature). Many biological
solutions, such as blood, have a pH near neutral.
Neutralization is a chemical reaction in which an acid and a base interact with the formation of a salt to make a solution neutral. With strong
acids and bases the important reaction is the combination of hydrogen ions with hydroxide ions to form water.
For example, when hydrochloric acid combines with equal proportions of sodium hydroxide, a full neutralization reaction takes place forming
Sodium Chloride and Water = HCl + NaOH  H2O + NaCL.
Bases neutralize acids (vice-versa) because the extra hydroxide ions (OH-) in a base, react with the extra hydrogen ions (H+) in an acid to form
water. However, this will only take place fully if the base provides enough hydroxide ions to neutralize each of the acid’s hydrogen ions. If the
resulting salt has neutral properties, the pH of the solution will be neutral.
These reactions are often exothermic (release heat). If the product of the reaction is not soluble in water (or more forms than water can
dissolve), it will precipitate out of solution as it forms. If the product of the reaction forms a gas that is not soluble (or more forms than water
can dissolve), it precipitates causing effervescence (fizz).
A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. It
has the property that the pH of the solution changes very little when a small amount of strong acid or base is added to it. Buffer solutions are
used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications. Many life forms thrive only in a relatively
small pH range; an example of a buffer solution is blood (which has chemicals that help maintain pH)
Materials:
 Test Tubes x5
 Graduated Cylinder (100m) (To measure volume)
 Graduated Cylinder (500m) (To measure volume)
 Acetic Acid (0.1M) x 15ml (1ml of 17.4M acetic acid to every
173ml of distilled water)
 Sodium Acetate x 0.10g
 Electronic Balance & Weigh Boat (to measure mass)
 Pipettes or Syringe (5ml) x5
 Beaker (50ml minimum) x 2
 Sodium Hydroxide (0.1M) x 10ml
 Hydrochloric Acid (0.1M) x 10ml
 Thermometer (Glass)
 Water (Distilled) x 173ml x # Factor (Depends on amount of
acetic acid required per class, this is certainly more than
enough for one)
Procedures
CAUTION: Students will be working with chemicals that could cause injury. All students should review proper safety laboratory procedures
prior to this experiment. All care should be taken to avoid spills and contact with skin or eyes. This includes the use of safety goggles, aprons,
and gloves. If there are any contact accidents, students should use emergency wash stations to wash eyes and sinks to wash hands. In case of
full body exposure, there should be an emergency shower stations in the laboratory. Teacher should be immediately notified of any such
emergency. Spills should also be notified immediately and properly cleaned.
1. Make the buffer solution: Measure 15 mL of 0.1 M acetic acid solution into a graduated cylinder (pour from stock vial and level off with
plastic syringe). Add 0.10 g. of sodium acetate to the graduated cylinder and swirl the mixture until the solid dissolves.
Note: Teacher can prepare buffer stock solution ahead of time and distribute about 25ml of solution for each group. This can be made by
simply multiplying volume of acetic acid and grams of sodium acetate by the # of groups required (suggestion: make enough for 1 extra
group).
2. Clean 6 test tubes thoroughly. Label them A, B, C, D, E, F and place them in a test tube stand.
3. Place a piece of pH paper in a clean watch glass or petri dish or tray
4. Prepare test tubes by adding chemicals in the following order:
Note: Each transfer should be made using a different pipette or 5ml syringe (in this case poor contents of graduated cylinder into cup or
Beaker) or they must be thoroughly washed/dried between each step. Stirring rod should be thoroughly washed/dried between each test.
1
2
4
6
7
8
Tube
Add 5ml of distilled water
Add 5ml of buffer solution
Use clean stirring rod to add a drop solution into a pH testing paper
Add 5ml of 0.1M hydrochloric acid
Add 5ml of 0.1M sodium hydroxide
Use clean stirring rod to add a drop solution into a pH testing paper
A
X
B
C
D
E
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
5.
6.
Pour contents of tube A into a Beaker.
Place a glass thermometer inside solution, wait for temperature to stabilize to get a temperature reading (do not remove thermometer)
Note: The use of a acid/base reaction safe probe might produce more accurate results
7. While watching the thermometer for any temperature change (Pour contents of tube E into the same beaker )
8. Note any temperature change and visual changes in the solution
9. Use a clean stirring rod to add a drop of solution into a pH testing paper
10. Dispose of all chemicals (as per teachers instructions) and clean all tubes
Results:
Tube
A
B
C
E
F
Initial
pH
After Acid/Base
A + B Solution
Beaker with A solution
ºC
Beaker after A+B are mixed
Visual changes in Solution A after
adding solution B
Analysis/Discussion:
1. When an acid and base combined what reaction results?
2. How do bases neutralize acids?
3. What are the chemical products of such reaction if it is complete?
4. What do you call chemicals that come “out-of-solution” during such a reaction?
5. What if the chemical is a gas?
6. While working in a lab, an unknown chemical spill occurs. Explain the process and observations you would use to determine if the
chemical is an acid , base, or neutral?
7. Assuming that the chemical spill above was potassium hydroxide (NaOH). What acid could you add to neutralize the base and what would
the products be?
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
Compare the initial pH with pH after acid treatment in test tube A and B. What was the effect of the buffer?
Compare the initial pH with PH after base treatment in test tube D and E. What was the effect of the buffer?
What was the purpose of test tube C?
What happened in steps 5-10 of the procedures? How can you tell?
Was there any temperature change? Why?
Explain the visual changes observed in A+B solution.
Infer the chemical composition of the A+B solution once reaction was completed
What is the pH of stomach juices? Why?
If bases neutralize acids, what happens if you eat something alkaline?
How would the body respond to this?
Based on your previous answers predict why the best long term way to fight heartburn and gastritis is not by ingesting a base.
How would you do it then?
What is the pH of human blood? Why?
Research the reaction for the bicarbonate-carbon dioxide buffer system and briefly explain how it works in the case of a patient
experiencing acidosis (can happen when too much carbon dioxide or monoxide is on the blood; breathing interruption)
Part D: Human Impact – Effects of Acid Rain
Objectives:
 Predict the impact of individuals on environmental systems and examine how human lifestyles affect sustainability. AA
 Discuss the large-scale environmental impacts resulting from human activity, including waste spills, oil spills, runoff, greenhouse gases,
ozone depletion, and surface and groundwater pollution.
Specific Purpose of the Lab/Activity:
 To determine the effects of acid rain on ecosystems
 To simulate the human impact on the environment.
Prerequisites:
 Students should be familiar with the pH scale.
 Students should be able to differentiate between an acid and a base.
 Students should be familiar with seed germination.
 Student should differentiate between global warming, acid rain, and ozone depletion.
Background: (Source: www.epa.gov)
The burning of fossil fuels during the industrialization of the world has caused many negative environmental impacts. Acid rain is a broad term
used to describe several ways that acids fall out of the atmosphere. A more precise term is acid deposition; which has two part wet and dry. Wet
deposition refers to acidic rain, fog, and snow. The strength of the effects depend on many factors, including how acidic the water is, the
chemistry and buffering capacity (the ability to neutralize acidic compounds) of the soils involved, and the types of fish, trees, and other living
things that rely on the water. Dry deposition refers to acidic gases and particles. The wind blows these acidic particles and gases onto buildings,
cars, homes, and trees.
Scientists discovered, and have confirmed, that sulfur dioxide (SO2) and nitrogen oxides (NOx) are the primary causes of acid rain. In the U.S.,
about 2/3 of all SO2 and 1/4 of all NOx comes from electric power generation that relies on burning fossil fuels like coal. Acid rain occurs when
these gases react in the atmosphere with water, oxygen, and other chemicals to form various acidic compounds. Sunlight increases the rate of
most of these reactions. The result is a mild solution of sulfuric acid (H 2SO4) and nitric acid (HNO3).
Acid rain is measured using a scale called pH. The pH scale measures how acidic or basic a substance is. It ranges from 0 to 14. A pH of 7 is
neutral. A pH less than 7 is acidic, and a pH greater than 7 is basic. Mixing acids and bases can cancel out their extreme effects; much like
mixing hot and cold water can even out the water temperature. Normal rain is slightly acidic because carbon dioxide (CO 2) dissolves in it, so it
has a pH of about 5.5. In recent years, the most acidic rain falling in the US has a pH of about 4.3.
Acid deposition has a variety of effects, including damage to forests and soils, fish and other living things, materials, and human health. Acid
rain also reduces how far and how clearly we can see through the air, an effect called visibility reduction.
Note that while global warming and ozone depletion are important human-related environmental problems associated with the atmosphere.
However, they are not directly tied to acid rain. Specific pollutants cause each problem.
Global warming occurs naturally as part of Earth’s ecological cycles and solar output changes. Human action may speed up global warming
because of increased greenhouse gas emissions (Carbon Dioxide, Methane Gas, Water Vapor). Note that each of these gases also occur
naturally (water evaporates from oceans; carbon dioxide comes from volcanoes, forest fires, and cellular respiration/fermentation
/decomposition processes; and methane is natural gas or a by-product of digestion/decomposition). As far as ozone depletion, it is caused by
chemicals that react with Ozone gas in the stratosphere. This includes (But not limited to) clorofluorocarbons (CFC’s). These used to be used
used in aerosol cans (still used in some countries), but this have been banned in most modern industries once the ozone layer depletion problem
was discovered and studied in the 80’s-90’s. Since then, the situation has “improved”, but it will still be decades until it is fully remediated (if
ever). Such chemicals are still used in many manufacturing processes in modern industries. They are also used in cooling applications
involving compressed gases or Freon gas (AC units, refrigeratios. industrial cooling, etc). If such equipment is not properly disposed and ends
up in landfills, gases are eventually released.
Acid rain is caused by another set of pollutants (sulfur and nitrogen based chemicals released from cars/factors during combustion processes)
that combine with water in the atmosphere to form acids (as mentioned above). Note that carbon dioxide and monoxide (also a greenhouse gas)
can also combine with water to make acids. However, they are much weaker than the acids produced from nitrogen and sulfur compounds
(Sulfuric; Nitric; etc).
Extension:
 Acid Rain Tutorial (from Environmental Protection Agency): http://www.epa.gov/acidrain/education/site_students/acid_anim.html
 Gizmo: Water Pollution
Research Question: How does the concentration of vinegar affect the germination of radish seeds?
Safety: Handle solutions carefully to avoid spills. The simulated “acid rain” solution may cause irritation and should be rinsed off promptly if
it comes into contact with the sun. Wear goggles at all times. If any of the solutions get into your eye, flush the eye with water for 15 minutes
and seek medical attention.
Pre-Lab:
1. What causes global warming? How are humans involved? Could it happen without us?
2. How have humans caused ozone depletion? What has been done to stop it?
3. Is the ozone layer still in danger? Why?
4. How are acid rain, global warming, and ozono depletion related? Does acid rain cause global warming or vice-versa? What about
ozone depletion? Answer all questions and explain your answer.
5. What would be a good problem statement for this lab (be specific)
6. Identify the independent and dependent variables for the lab
7. Create a hypothesis for the lab
8. Identify other possible variables that should be held constant during the lab
9. Good experimental designs involve repetition, how would you modify the experimental design suggested to gather data that are more
reliable?
10. What will happen to environmental pH if pollution adds acids to clouds?
11. What industries in our area pump materials into the atmosphere to create a drastic change in rain water? (Hint: Some days you can
smell this industry.)
12. Based on what you learned, list substances that would cause death of organisms in aquatic ecosystems?
Materials (per group):
 graduated cylinder (if prepping solutions)
 filter paper x 5 (per group)
 600ml Beaker (or bottle) x # of samples
 5ml syringes x # of beakers (5 if pre-prepared solutions or 2 if
Vinegar vs. Water
 pH meter




5 Petri dishes
water
vinegar (or acetic acid 0.1M) x
25 radish seed
Procedures:
Optional (Teacher): Prepare vinegar solutions following % rations (For example: 25% vinegar + 75% distilled water for the 50% solution).
Alternatively, simply prepare 2 Beakers; one for Vinegar & one for water, and have students draw samples to create solutions in petri dishes (as
outlined in step 2).
1.
2.
3.
4.
5.
6.
7.
8.
Label one Petri dish for each of the following treatments: 100%, 75%, 50%, 25%, and 0%.
Create vinegar solutions inside petri dishes using the following measurement (or taking 5ml samples directly from pre-prepared solutions)
Use 5ml syringes to draw from stock solutions (a different syringe should be used with each solution):
Sample
Vinegar
H2O
100%
5ml
0ml
75%
3.75ml
1.25ml
50%
2.5ml
2.5ml
25%
1.25ml
3.75ml
0%
0ml
5ml
Place 1-3 pieces of filter paper / toilet paper into each dish.
Test the pH of each solution using paper strips or one of the methods used in Part B (can be tested once per class to save resources)
Place 5 seeds in each treatment.
Place the Petri dishes in the box in front of the room.
After 5 days, remove the Petri dishes and check to see how many seeds have germinated (sprouted).
Record your data in the chart. Note any changes in the appearance of the seeds.
Observations/Data:
Percentage of Vinegar
100%
75%
50%
25%
0%
pH
# of Radish Seeds
Germinated
Changes in Appearance
Class Average
Data Analysis:
Create a line graph using the data from the table above; make sure to label your axis(s) and include the units of measurements. If available,
graph class average
Mr. DRY MIX: the Dependent variable is the Responding variable that in a graph is recorded on the Y-axis; the Manipulated variable is the
Independent variable and is graphed on the X-axis
Discussion Questions:
1. Why did the data analysis section suggested the use of class averages?
2. What effects do acid rain have on living systems?
3. How can we contribute to reducing problems such as global warming, ozone depletion, and acid rain?
4. Identify the relationship between pH and vinegar concentration.
5. Is vinegar an acid? Explain how that can be inferred from this activity.
6. Compare your results with the class; were there any differences in the germination or pH by lab group? Is so, speculate on possible
reasons for these differences.
7. Under which vinegar concentration did the seeds germinate best? Is this consistent with your expectations?
8. What effect does the varying concentration have on seed germination?
9. Predict what would happen if I applied a basic solution instead of an acid solution to seed germination.
10. Predict how the results of this experiment can be used to explain the effects of acid rain on our environment.
11. Explain how acidic water can harm aquatic plants and animals.
12. Give five examples of animal physiological or behavioral adaptions that can help organism maintain pH balance? Why is this
important?
Part E: Inquiry Extension
Research Question: How do changes in pH affect important living systems?
Direction: Students must design their own experiment to answer this research question. Procedures must be submitted to teacher for approval.
After procedure approval, students will have access to lab equipment (if available), but all chemicals used must be provided by students . Full
lab reports (following rubric/template) must be submitted at the conclusion of the experiment.
Tips: pH can be manipulated using easily accessible substances like the ones used in the unknown in part B. Students can examine effects of
pH on aquatic ecosystems (fish tanks), microscopic (bacterial cultures on slants / petri dishes), or terrestrial (terrarium). All systems must
include at least 3 organisms.