Acid Base Chemistry
Big Chemistry Project
SME 401
Dominic Held
This packet includes five days of activities to be used in a high school chemistry class.
These activities should accompany a 2-3 week long unit on acid base chemistry.
Activities:

Rainbow Connection Demonstration- Introduces acids and bases in a visual way.
Students will observe indicators and their response to changes in pH. They will also
observe how pH change can be a reversible process. This could be the first day
beginning a unit a acid base chemistry.

Measuring pH of Household Chemicals- This two day activity should follow several
days of instruction on acids and bases. The pH scale should also be introduced in terms
of concentration of H+ and OH- ions. The second part of this experiment is dependent on
the availability of computer interfaced probes. The procedure of this part should be
expanded or supplemented accordingly. If probes are unavailable the second day may be
omitted.

How Does a Buffer Affect pH?- This experiment should follow a discussion of buffer
solutions in terms of H+ cations, OH- anions, and disassociation of weak and strong
bases. Students should also be able to recognize the acid and base components of
conjugate acid/base pairs.

Microscale Titration-This activity uses phenolphthalein to indicate when an acidic acid
has been titrated with a NaOH solution. By knowing the normality of the NaOH solution
and the amount of drops used to titrate the acidic acid solution, the normality of an acidic
acid solution can be calculated. This experiment should follow several lectures on the
normality of solutions. Students should also be familiar with different measures of
concentrations including molarity and molality.
Teacher Support Materials:
Rainbow Connection Demonstration
Overview:
This demonstration will be an introduction to a weeks worth of activities exploring acid/base
chemistry. Several different ph indicators will be used to produce a wide array of colors. These
indicators will be colorless under acidic conditions, but when a base is added, they will produce
the three primary colors. By carefully mixing the indicators, all the colors of the rainbow will be
produced. Six beakers are filled with the same “mystery” liquids. Each glass beaker takes on a
different color of the rainbow, despite the fact that the same liquids were added to each. These
solutions can be used several times and have a good shelf life.
Teacher and Student Objectives:



Shows the dramatic color change of solutions containing indicators at different pH levels.
Demonstrates the reversibility of indicator color changes.
Get students thinking about how H+ and OH- ions interact.
Who’s Being Taught?
This demonstration could be used in both junior and high school when covering acids bases and
indicators. Class size can vary considerably. It could even be given to a large audience given the
proportions are increase to increase visibility.
Strengths of Exercise:




This is a vivid exercise that should hold the student’s interest.
The idea that you are performing magic using ‘mystery’ solutions can be used to increase
their interest.
This demonstration makes a great introduction to acid/base chemistry.
Easy disposal of chemicals.
How to Assess:
Assign the students the readings in their textbooks that begin with acid base chemistry. Be sure
to include readings on pH indicators. Students then should have some understanding about how
this lab was executed.
What to Look Out For:




Precautions should be taken when making solutions. (Safety Glasses)
Students will not be handling solutions so it should be safe if they don’t wear safety
glasses. This would also depend on school policy.
Beakers should be visible to the entire audience.
Demonstration should be tested before presenting.
Technical Information:
The solutions in this demonstration should be prepared at least a day before the presentation.
Some thought should be given on how this demonstration should be given.
Materials:








6 250 mL Beakers
6 Indicator Solutions and 6 droppers
500 mL Acid-Alcohol Solution
1200 mL 0.012 M NaOH Solution
100 mL 0.2 M NaOH Solution and 1 dropper bottle
30 mL Glycerine Solution and 1 dropper bottle
1 Small Beaker (35 mL)
2 Large Pitchers
Procedure:
Indicators:
The following recipes are for the six different indicator solutions. Each recipe will produce 15
mL of solution. These solutions should be made at least one day in advance to allow the solutes
to fully dissolve into solution. Use 15 mL of 95% ethanol as the solvent for all six solutions.
 Red0.4 g phenolphthalein plus 1.0 g m nitrophenol
 Orange0.15 g phenolphthalein plus 2.0 g m nitrophenol
 Yellow2.0 g m nitrophenol
 Green0.2 g thymolphthalein plus 2.0 g m nitrophenol
 Blue0.5 g thymolphthalein
 Violet0.3 g phenolphthalein plus 0.13 g thymolphthalein
Acid-Alcohol Solution:
Mix 250 mL 0.05 M aqueous sulfuric acid with 250 mL 95% ethanol. Transfer into a large
pitcher.
NaOH Solutions:
Prepare 1200 mL of 0.012 M NaOH solution transfer into a large pitcher. Make sure you know
which pitcher is the acid and which is the base.
Prepare 100 mL of 0.2 M NaOH solution and transfer into a dropper bottle.
Glycerine Solution:
Dissolve 10 mL of 18 M H2SO4 in 20 mL of glycerol. Transfer into a dropper bottle.
Before Class:
1. Arrange the six 250 mL beakers in a row so that they can be seen by the entire class.
Carefully place 2 drops of indicator solution in the middle of the beaker in the order
shown:
2. Let the indicator solution dry on the bottom of the glass. This should take about 30
minutes.
During Class:
1. Add 35 mL of the acid, making sure to carefully pour down the side of the beaker. Try
not to disturb the dried indicator. This solution should remain clear.
2. Slowly fill each beaker half full with the 0.012 NaOH solution. Once again be careful
not to disturb the indicator by pouring along the side of the beaker. The amount of this
solution should not be enough to make the solution in the beaker basic, so the solution
should remain colorless
3. Rapidly pour the 0.012 NaOH solution into the beakers nearly to the top. The color of
the solutions should now be visible. You may have to stir the solutions in order to fully
dissolve the indicator.
4. Add anywhere from 3-15 drops of the glycerine solution stirring vigorously. Prior testing
should give you an idea how much is needed to raise the acidity of the solutions until
they are clear.
5. Titrate each beaker back to its original color by adding the 0.2 M NaOH solution drop
wise and stirring vigorously.
6. Sneak 2 droppers full of the glycerine solution into the large pitcher containing the 0.012
NaOH solution.
7. Pour the contents of each of the beakers into the now acidic NaOH-glycerine pitcher.
Because of the acidity of this solution, the combined solution should be colorless.
8. The solution mixture in the pitcher can be poured down the drain.
Follow up:
Assign the students the readings in their textbooks that begin with acid base chemistry. Be sure
to include readings on pH indicators. Students then should have some understanding about how
this lab was executed.
Measuring pH of Household Chemicals
Overview:
Many common household chemicals have acidic or basic properties. Scientists use the pH scale
to rate acidity in solutions. The pH of a solution is a measure of the concentration of hydrogen
ions in that solution. There are several different ways to measure pH. A pH indicator can be
used to qualitatively determine the acidity or basesity of a solution. pH indicators are usually
weak acids or bases themselves. When introduced into a solution, they may bind to H+
(Hydrogen ion) in an acid or the OH- (hydroxide) ions in a base. The change in electron
configurations of the indicator causes the indicator's color to change. In this activity we will use
cabbage juice and pH paper to determine an estimate of several household chemical’s pH. For
the second part of the lab we will use a computer interfaced probe to find a more accurate
measure of these chemicals pH.
Objectives:





Use red cabbage juice as a pH indicator by recording its color change in various
chemicals.
Use pH paper to obtain a more accurate measure of pH, including a numerical value.
Set up and calibrate a computer interfaced pH probe.
Use pH probe to take an even more accurate pH measure.
Compare results and correlate a pH scale for the red cabbage juice indicator.
Materials:
Day 1:
 Red Cabbage Juice
 6-Well Reaction Plates
 Transfer Pipettes
 Various Household Chemicals (Baking soda solution, solution of detergent, Soda, milk of
magnesia, vinegar, glass cleaner, etc)
 pH Paper
Day 2:
 Computer Interfaced pH Meter (with instructions)
 Buffer Solutions for Calibration of Probe
 Six Small Beakers
Procedure:
Day 1: Correlating cabbage juice color and pH in various solutions using pH paper
1. Obtain a 6-well reaction plate. Label the wells 1-6
2. Obtain six different household chemicals and place them in individual wells. Use the
chart below to record which chemical is in which well.
3. Use pH paper to determine the pH of each substance. Compare the color change of the
paper to the key given with the pH paper. Again use the chart below to record your
results.
4. Using a transfer pipette, add 5 drops of red cabbage juice into each well. If no color
change occurs add 5 more drops. Record the color of each well in the chart below.
Day 2: Correlating cabbage juice color with pH measured using a computer interfaced
probe.
1. Setup the computer interfaced probe as indicated by your instructor. Be sure to have a
beaker of distilled water to rinse the probe between uses.
2. Following the directions given with the probe, calibrate the probe using the supplied
buffer solutions with known pH.
3. Label 6 beakers 1-6 and use the same solutions in the same configuration as yesterday.
Pour each solution to be tested into a small beaker. There should be enough liquid in
each beaker so that the probe will be completely immersed. Record the readings for each
substance in the chart below.
4. Add 10 drops of red cabbage indicator into the solutions and record the color change.
5. After completing the experiment, wash the probe with distilled water and return the
electrode to the storage solution.
Analysis:
Solution #
Solution Name
Day 1
pH solution
w/ pH paper
Day 2
Color w/
pH solution
cabbage juice w/ probe
Color w/
cabbage juice
1
2
3
4
5
6
Follow-up:
1. What is the pH of a solution a measure of?
2. What is the concentration of H+ ions in a solution with a pH of 1?
3. Did the pH values obtained in day 1 agree with those in day 2?
4. Using the data compiled in this activity, what would be the color of a solution with a pH
of 4 if red cabbage is added?
5. Do you see any pattern in the type of substances used and their pH?
Assessment:
Participation- Student is on task, working well with group. Instructor should not have to settle
disputes between group members on how and who will complete the objectives of the exercise.
Lab Report- This includes data for day 1 and day 2.
Essay questions: Each student will submit their responses to the essay questions. Responses
will be graded on completeness, thoughtfulness, grammar, punctuation, and spelling.
Lab Report and essay questions will be submitted on time. No late work will be accepted
without a written excuse from a parent or doctor.
Participation in Data Collection ----------------30 pts
Lab Report ----------------------------------------30 pts
Essay Questions-----------------------------------40 pts
Total---------------------------------------------100 pts
Measuring pH of Household Chemicals
Teacher Support Materials
Overview:
This two day activity should follow several days of instruction on acids and bases. The pH scale
should also be introduced in terms of concentration of H+ and OH- ions. Students should know
how to calculate the concentration of H+ ions in a solution given its pH. The second part of this
experiment is dependent on the availability of computer interfaced probes. The procedure of this
part should be expanded or supplemented accordingly. If probes are unavailable the second day
may be omitted.
Teacher and Student Objectives:







Use red cabbage juice as a pH indicator by recording its color change in various
chemicals.
Use pH paper to obtain a more accurate measure of pH, including a numerical value.
Set up and calibrate a computer interfaced pH probe.
Use pH probe to take an even more accurate pH measure.
Compare results and correlate a pH scale for the red cabbage juice indicator.
Give students real life examples of acids and bases.
Introduce students to computer interfaced probes for future experiments.
Who’s Being Taught?




High school chemistry 10-12 grade
20-25 students
Groups of 2-3 students
Students should be instructed on where to find the materials needed to complete this
activity
How to Assess:
Participation- Student is on task, working well with group. Instructor should not have to settle
disputes between group members on how and who will complete the objectives of the exercise.
Lab Report- This includes data for day 1 and day 2.
Essay questions: Each student will submit their responses to the essay questions. Responses
will be graded on completeness, thoughtfulness, grammar, punctuation, and spelling.
Lab Report and essay questions will be submitted on time. No late work will be accepted
without a written excuse from a parent or doctor.
Participation in Data Collection ----------------30 pts
Lab Report ----------------------------------------30 pts
Essay Questions-----------------------------------40 pts
Total---------------------------------------------100 pts
Strengths of Exercise:




Connects everyday substances to acid base chemistry.
Gives students practice taking pH measurements with pH paper.
Shows correlation of acidic foods and basic cleaners
Relatively safe chemicals that are easily disposed of.
What to Look Out For:





Although these are household chemicals, safety glasses may need to be worn depending
on the policy of your school.
Proper safety equipment should be assessable and in working order (eye bath, shower,
etc)
Spills should be anticipated with proper cleanup methods in place.
Careless students should be approached and reminded of the potential dangers when
working with chemicals.
Red cabbage juice may stain clothes, have aprons available.
Materials:
Preparation of cabbage juice indicator:
 Red Cabbage
 Cheese Cloth
 Knife
 Pan
Day 1:
 Red Cabbage Juice
 6-Well Reaction Plates
 Transfer Pipettes
 Various Household Chemicals (Baking soda solution, solution of detergent, Soda, milk of
magnesia, vinegar, glass cleaner, etc)
 pH Paper
Day 2:
 Computer Interfaced pH Meter (with instructions)
 Buffer Solutions for Calibration of Probe
 Six Small Beakers
Procedure:
Preparation of red cabbage juice indicator:
1. Coarsely cut up ½ a head of lettuce.
2. Place in pan with enough water to immerse the lettuce.
3. Bring to boil and simmer for 10 minutes.
4. Allow to cool.
5. Filter through cheesecloth.
6. Keep refrigerated until needed.
Day 1: Correlating cabbage juice color and pH in various solutions using pH paper
1. Obtain a 6-well reaction plate. Label the wells 1-6
2. Obtain six different household chemicals and place them in individual wells. Use the
chart below to record which chemical is in which well.
3. Use pH paper to determine the pH of each substance. Compare the color change of the
paper to the key given with the pH paper. Again use the chart below to record your
results.
4. Using a transfer pipette, add 5 drops of red cabbage juice into each well. If no color
change occurs add 5 more drops. Record the color of each well in the chart below.
Day 2: Correlating cabbage juice color with pH measured using a computer interfaced
probe.
1. Setup the computer interfaced probe as indicated by your instructor. Be sure to have a
beaker of distilled water to rinse the probe between uses.
2. Following the directions given with the probe, calibrate the probe using the supplied
buffer solutions with known pH.
3. Pour each solution to be tested into a small beaker. There should be enough liquid in
each beaker so that the probe will be completely immersed. Record the readings for each
substance in the chart below.
4. Add 10 drops of red cabbage indicator into the solutions and record the color change.
5. After completing the experiment, wash the probe with distilled water and return the
electrode to the storage solution.
Sample Data:
Solution #
Solution Name
1
2
Vinegar
Glass cleaner
3
4
5
Shower cleaner
Baking soda
Calcium
Carbonate
Epson salt
Sprite
6
7
pH solution
w/ pH paper
2
10
pH solution
w/ probe
2
10
2
8
6
Color w/
cabbage juice
Pinkish red
Yellowish
green
Dark pink
Light blue
Light pink
2
8
6.4
Color w/
cabbage juice
Pinkish red
Yellowish
green
Dark pink
Light blue
Light pink
6
4
Light purple
Pink
6
4
Light purple
Pink
How Does a Buffer Affect pH?
Overview:
A buffer solution is combination of a weak acid and its conjugate base. When a strong
acid is added to a buffer solution, the conjugate base associates with the H+ ions of the strong
acid. This preserves the pH of the solution. Likewise, if a strong base is added, the weak acid
will associate with OH- ions. Buffers are most effective when the concentrations of the acid and
base are equal. In this experiment, acetic acid and sodium acetate will be combined to create a
buffer solution with a pH approximately equal to its pKa. The resistance to pH change of this
buffer will be compared to a HCl solution and distilled water by adding strong acids and bases
and measuring the pH with pH paper.
Objectives:




Create a buffer using equal amounts of acetic acid and sodium acetate.
Measure pH changes in solutions when an acid or base is added to them.
Compare these pH changes in a strong acid, distilled water, and a buffer solution.
Find an approximate value for the pKa of acetic acid and sodium acetate.
Materials:



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


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2, 24 well reaction plates
Transfer pipettes
4.8 pH HCl solution
0.5 M acetic acid
0.5 M sodium acetate
pH paper
0.1 M HCl
0.1 M NaOH
10 mL graduated cylinder
Procedure:
Groups of 2 will be assigned.
1. Students must wear safety goggles at all times.
2. Combine 5 mL of 0.5 M acetic acid with 0.5 M sodium acetate to create a buffer.
3. Add 15 drops of pH 4.8 HCl solution to nine wells of your 24-well reaction plate.
4. Test the pH of one of these wells with pH paper. Record in data table.
5. Add 15 drops of 4.8 buffer solution to nine different wells of your 24-well.
6. Test the pH of one of these wells with pH paper. Record in data table.
7. In a second 24-well plate, add 15 drops of distilled water into 9 wells.
8. Test the pH of one of these wells with pH paper. Record in data table.
9. Add 15 drops of distilled water to 3 wells of 4.8 pH HCl, 4.8 pH buffer, and distilled
water.
10. Use pH paper to record the pH of one of these wells for each type of solution.
11. Add 3 drops of 0.1 M HCl to 3 wells of HCl solution, buffer solution, and distilled water.
12. Use pH paper to record the pH of one of these wells for each type of solution.
13. Add 3 drops of 0.1 M NaOH to 3 wells of HCl solution, buffer solution, and distilled
water.
14. Use pH paper to record the pH of one of these wells for each type of solution.
Calculations:
Solution
Initial pH
pH after 15
drops H2O
pH after 3
drops 0.1 M
HCl
pH after 3
drops 0.1 M
NaOH
HCl
Buffer
H2 0
pH = pKa + log [base]/[acid]
Follow-up:
1. Was there a difference in the pH change of the buffer with respect to the HCl and water?
2. Describe what is happening at the molecular level when an acid is added to each of the
three solutions.
HClH2OBuffer3. Discuss how a buffer solution resists pH change when a strong base is added to it.
4. What is the approximate pKa of pKa of acetic acid and sodium acetate?
Assessment:
Participation- Student is on task, working well with group. Instructor should not have to settle
disputes between group members on how and who will complete the objectives of the exercise.
Lab Report- This includes data and calculations. Accuracy of the data is not as important as
the proper use of the calculations.
Essay questions: Each student will submit their responses to the essay questions. Responses
will be graded on completeness, thoughtfulness, grammar, punctuation, and spelling.
Lab Report and essay questions will be submitted on time. No late work will be accepted
without a written excuse from a parent or doctor.
Participation in Data Collection ----------------30 pts
Lab Report ----------------------------------------30 pts
Essay Questions-----------------------------------40 pts
Total---------------------------------------------100 pts
How Does a Buffer Affect pH?
Teacher Support Materials
Overview:
This experiment should follow a discussion of buffer solutions in terms of H+ cations, OHanions, and disassociation of weak and strong bases. Students should also be able to recognize
the acid and base components of conjugate acid/base pairs. This experiment will also give
students a chance to work with buffer solutions and observe their resistance to pH change.
A buffer solution is combination of a weak acid and its conjugate base. When a strong acid is
added to a buffer solution, the conjugate base associates with the H+ ions of the strong acid. This
preserves the pH of the solution. Likewise, if a strong base is added, the weak acid will associate
with OH- ions. Buffers are most effective when the concentrations of the acid and base are equal.
In this experiment, acetic acid and sodium acetate will be combined to create a buffer solution
with a pH approximately equal to its pKa. The resistance to pH change of this buffer will be
compared to a HCl solution and distilled water by adding strong acids and bases and measuring
the pH with pH paper.
Teacher and Student Objectives:




Create a buffer using equal amounts of acetic acid and sodium acetate.
Measure pH changes in solutions when an acid or base is added to them.
Compare these pH changes in a strong acid, distilled water, and a buffer solution.
Find an approximate value for the pKa of acetic acid and sodium acetate.
Who’s Being Taught:




High school chemistry 10-12 grade
20-25 students
Groups of 2-3 students
Students should be instructed on where to find the materials needed to complete this
activity
How to Assess:
Participation- Student is on task, working well with group. Instructor should not have to settle
disputes between group members on how and who will complete the objectives of the exercise.
Lab Report- This includes completion of table of pH measurements of buffer, HCl, distilled
water.
Essay questions: Each student will submit their responses to the essay questions. Responses
will be graded on completeness, thoughtfulness, grammar, punctuation, and spelling.
Lab Report and essay questions will be submitted on time. No late work will be accepted
without a written excuse from a parent or doctor.
Participation in Data Collection ----------------30 pts
Lab Report ----------------------------------------30 pts
Essay Questions-----------------------------------40 pts
Total---------------------------------------------100 pts
Strengths of Exercise:




Helps students gain a better understanding of pH and disassociation constants and their
connectedness.
Gives students practice taking pH measurements with pH paper.
Easy setup and cleanup.
This experiment will also give students a chance to work with buffer solutions and
observe their resistance to pH change.
What to look out for:






Students should be wearing safety goggles at all times.
Proper safety equipment should be assessable and in working order (eye bath, shower,
etc)
Spills should be anticipated with proper cleanup methods in place.
Careless students should be approached and reminded of the potential dangers when
working with chemicals.
The chemicals in this lab may cause damage to students clothes, have aprons available.
Students may need assistance with the calculations in this activity.
Technical Information:


This experiment should follow a discussion of buffer solutions in terms of H+ cations,
OH- anions, and disassociation of weak and strong bases.
Students should also be able to recognize the acid and base components of conjugate
acid/base pairs.
Materials:









2, 24 well reaction plates
Transfer pipettes
4.8 pH HCl solution
0.5 M acetic acid
0.5 M sodium acetate
pH paper
0.1 M HCl
0.1 M NaOH
10 mL graduated cylinder
Procedure:
Preparation of pH 4.8 HCl solution:
Dilute 0.5 M HCl 1:2, dilute this 0.25 M HCl 1:100, dilute this 0.0025 M HCl 1:100.
This gives a final concentration of 0.000025 M or 2.5 x 10-5 M
Groups of 2 will be assigned.
1. Students must wear safety goggles at all times.
2. Combine 5 mL of 0.5 M acetic acid with 0.5 M sodium acetate to create a buffer.
3. Add 15 drops of pH 4.8 HCl solution to nine wells of your 24-well reaction plate.
4. Test the pH of one of these wells with pH paper. Record in data table.
5. Add 15 drops of 4.8 buffer solution to nine different wells of your 24-well.
6. Test the pH of one of these wells with pH paper. Record in data table.
7. In a second 24-well plate, add 15 drops of distilled water into 9 wells.
8. Test the pH of one of these wells with pH paper. Record in data table.
9. Add 15 drops of distilled water to 3 wells of 4.8 pH HCl, 4.8 pH buffer, and distilled
water.
10. Use pH paper to record the pH of one of these wells for each type of solution.
11. Add 3 drops of 0.1 M HCl to 3 wells of HCl solution, buffer solution, and distilled water.
12. Use pH paper to record the pH of one of these wells for each type of solution.
13. Add 3 drops of 0.1 M NaOH to 3 wells of HCl solution, buffer solution, and distilled
water.
14. Use pH paper to record the pH of one of these wells for each type of solution.
Calculations:
Solution
Initial pH
pH after 15
drops H2O
pH after 3
drops 0.1 M
HCl
pH after 3
drops 0.1 M
NaOH
HCl
Buffer
H2 0
Follow-up:
1. Was there a difference in the pH change of the buffer with respect to the HCl and water?
2. Describe what is happening at the molecular level when an acid is added to each of the
three solutions.
HClH2O-
Buffer3. Discuss how a buffer solution resists pH change when a strong base is added to it.
What is the approximate pKa of pKa of acetic acid and sodium acetate?
Sample Data:
Solution
Initial pH
pH after 15
drops H2O
HCl
Buffer
H2 0
5
5
7
6
5
7
pH after 3
drops 0.1 M
HCl
5
5
6
pH after 3
drops 0.1 M
NaOH
11
6
11
Microscale Titration
Overview:
In this experiment, the microscle method of titration will be used to determine the gram
molecular weight (GMW) of citric acid by titration with NaOH. Phenolphthalein is colorless
under acidic conditions. As NaOH is added the acidity of the solution is neutralized as OH- ions
bond with H+ ions to form H2O. When the concentration of the OH- and H+ ions reach
equilibrium, the phenolphthalein will no longer be bonded to H+ ions. When equilibrium is
reached, the electron configuration of the phenolphthalein molecules undergo a change that
results in a color change from colorless to pink. Using the experimental GMW, the normality of
citric acid will be calculated. Phenolphthalein will be used to indicate when the titration is
complete. With just 1 to 2 drops of phenolphthalein, the color of the solution will be colorless
when it is acidic, and become pink when the solution is neutralized.
This titration will be performed on a micro scale. Instead of measuring the volume of
acid and bases used, drops from a transfer pipette will be counted.
Objectives:




Gain experience with precision when working with the small amount of solution that is
used.
Introduction to the method of titrations.
Calculate the gram molecular weight of citric acid using their data.
Determine the unknown normality of the given citric acid solution.
Materials:
24 well reaction plates
Transfer pipettes
0.2 M NaOH
Coffee stirrers
Phenolphthalein
Procedure:
Groups of 2 will be assigned.
1. Students must wear safety goggles at all times.
2. Using the 1.0 M NaOH solution that is given, make a small sample of a 0.2 M solution of
NaOH.
3. Using your transfer pipette place seven drops of citric acid to each of five wells.
4. Add one drop of phenolphthalein to those five wells.
5. Counting each drop, begin adding 0.2 M NaOH stirring the solution as you go.
6. When the solution stays pink despite stirring, the solution has been neutralized. Record
the number of drops of NaOH that were added.
7. Calculate normality using the equations that follow.
8. Calculate the experimental value of the gram molecular weight of the citric acid.
Calculations:
We diluted solutions to lower Molarity in previous labs. Give your calculations for
diluting a 1.0 M NaOH solution into a 0.2 M NaOH solution.
Trial
#1
#2
#3
#4
Average
GMW
# drops
C6H8O7
# drops
indicator
# drops
0.2M NaOH
moles acid
Normality of
given citric acid
The given citric acid solution is 100 g/L. NaOH has a normality of 1, our solution is 0.2 N
Normality = [NaOH] x (drops of NaOH/drops of citric acid)
GMW = Concentration (in g/L) of citric acid in solution x 3 equivalents
Normality of citric acid
Molarity of citric acid = 1 / (GMW x 1L/100g)
Follow-up:
1. What is the molecular weight of citric acid?
2. What is the molecular weight of NaOH?
3. How many OH- ions can one molecule of NaOH produce?
4. How many H+ ions can one molecule of citric acid produce?
5. How does this affect the titration of citric acid with NaOH?
6. What was your experimental normality of the citric acid?
Assessment:
Participation- Student is on task, working well with group. Instructor should not have to settle
disputes between group members on how and who will complete the objectives of the exercise.
Lab Report- This includes data and calculations. Accuracy of the data is not as important as
the proper use of the calculations.
Essay questions: Each student will submit their responses to the essay questions. Responses
will be graded on completeness, thoughtfulness, grammar, punctuation, and spelling.
Lab Report and essay questions will be submitted on time. No late work will be accepted
without a written excuse from a parent or doctor.
Participation in Data Collection ----------------20 pts
Lab Report ----------------------------------------40 pts
Essay Questions-----------------------------------40 pts
Total---------------------------------------------100 pts
Microscale Titration
Teacher Support Materials
Overview:
This activity uses phenolphthalein to indicate when an acidic acid has been titrated with a NaOH
solution. By knowing the normality of the NaOH solution and the amount of drops used to
titrate the acidic acid solution, the normality of an acidic acid solution can be calculated. This
experiment should follow several lectures on the normality of solutions. Students should also be
familiar with different measures of concentrations including molarity and molality.
In this experiment, the microscle method of titration will be used to determine the gram
molecular weight (GMW) of citric acid by titration with NaOH. Phenolphthalein is colorless
under acidic conditions. As NaOH is added the acidity of the solution is neutralized as OH- ions
bond with H+ ions to form H2O. When the concentration of the OH- and H+ ions reach
equilibrium, the phenolphthalein will no longer be bonded to H+ ions. When equilibrium is
reached, the electron configuration of the phenolphthalein molecules undergo a change that
results in a color change from colorless to pink. Using the experimental GMW, the normality of
citric acid will be calculated. Phenolphthalein will be used to indicate when the titration is
complete. With just 1 to 2 drops of phenolphthalein, the color of the solution will be colorless
when it is acidic, and become pink when the solution is neutralized.
This titration will be performed on a micro scale. Instead of measuring the volume of acid and
bases used, drops from a transfer pipette will be counted.
Teacher and Student Objectives:
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Gain experience with precision by working with small amounts of solution.
Introduction to the method of titrations.
Calculate the gram molecular weight of citric acid using their data.
Determine the unknown normality of the given citric acid solution.
Who’s Being Taught:
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High school chemistry 10-12 grade
20-25 students
Groups of 2-3 students
Students should be instructed on where to find the materials needed to complete this
activity
How to Assess:
Participation- Student is on task, working well with group. Instructor should not have to settle
disputes between group members on how and who will complete the objectives of the exercise.
Lab Report- This includes data and calculations. Accuracy of the data is not as important as
the proper use of the calculations.
Essay questions: Each student will submit their responses to the essay questions. Responses
will be graded on completeness, thoughtfulness, grammar, punctuation, and spelling.
Lab Report and essay questions will be submitted on time. No late work will be accepted
without a written excuse from a parent or doctor.
Participation in Data Collection ----------------20 pts
Lab Report ----------------------------------------40 pts
Essay Questions-----------------------------------40 pts
Total---------------------------------------------100 pts
Strengths of Exercise:
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Good introduction to titrations.
Small amounts of chemicals are used.
Dramatic color change that is easily observed.
Students will gain experience in diluting solutions.
What to look out for:
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Students should be wearing safety goggles at all times.
Proper safety equipment should be assessable and in working order (eye bath, shower,
etc)
Spills should be anticipated with proper cleanup methods in place.
Careless students should be approached and reminded of the potential dangers when
working with chemicals.
The chemicals in this lab may cause damage to students clothes, have aprons available.
Students may need assistance with the calculations in this activity.
Technical Information:
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This experiment should follow several lectures on the normality of solutions.
Students should be able to calculate the molecular weight of compounds given a periodic
table.
Students should also be familiar with different measures of concentrations including
molarity and molality
A large solution of 1.0 M NaOH should be prepared for students before the lab.
Students will need to be given the chemical formula of the acidic acid solution.
Materials:
24 well reaction plates
Transfer pipettes
1.0 M NaOH
Procedure:
Groups of 2 will be assigned.
Coffee stirrers
Phenolphthalein
1. Students must wear safety goggles at all times.
2. Using the 1.0 M NaOH solution that is given, make a small sample of a 0.2 M solution of
NaOH.
3. Using your transfer pipette place seven drops of citric acid to each of five wells.
4. Add one drop of phenolphthalein to those five wells.
5. Counting each drop, begin adding 0.2 M NaOH stirring the solution as you go.
6. When the solution stays pink despite stirring, the solution has been neutralized. Record
the number of drops of NaOH that were added.
7. Calculate normality using the equations that follow.
8. Calculate the experimental value of the gram molecular weight of the citric acid.
Calculations:
We diluted solutions to lower Molarity in previous labs. Give your calculations for
diluting a 1.0 M NaOH solution into a 0.2 M NaOH solution.
Trial
#1
#2
#3
#4
Average
GMW
# drops
C6H8O7
# drops
indicator
# drops
0.2M NaOH
moles acid
Normality of
given citric acid
The given citric acid solution is 100 g/L. NaOH has a normality of 1, so our solution is 0.2
N
Normality = [NaOH] x (drops of NaOH/drops of citric acid)
GMW = Concentration (in g/L) of citric acid in solution x 3 equivalents
Normality of citric acid
Molarity of citric acid = 1 / (GMW x 1L/100g)
Follow-up:
1. What is the molecular weight of citric acid?
2. What is the molecular weight of NaOH?
3. How many OH- ions can one molecule of NaOH produce?
4. How many H+ ions can one molecule of citric acid produce?
5. How does this affect the titration of citric acid with NaOH?
6. What was your experimental normality of the citric acid?
Sample Data
Trial
1
2
3
4
Average
GMW
C6H8O7
7
7
7
7
7
192.3
Indicator
1
1
1
1
1
Normality of
citric acid
(0.2 x 54.5) / (0.521 x 7) = 2.99
0.2M NaOH
56
55
53
54
54.5
0.521
moles acid
1.60
1.51
1.51
1.54
1.56