Lesson Plan for Mixing Acids and Bases
Topic of Lesson: Mixing acids and bases
Length of lesson: 2 – 50 minute class periods
Subject: Chemistry
Grade Level: 11-12th Grade
Objectives:
-The student will describe how combining acids and bases produce a neutral solution.
(Grade 9-12.Standard II.B.5)
Rationale/Purpose: The students should understand the effects of adding acids to
bases and vice versa so they can determine how a neutral solution can be made, which
has real-world significance when dealing with acid indigestion or acid rain.
Preparation:
Day 1: The students need to have access to computers.
Day 2: The following materials need to be available for the lab:
-1.0 M HCl
-Glass stirring rod
-1.0 M NaOH
-Test tube rack
-Bromothymol Blue indicator
-Table clamp
-Mortar and pestle
-100 mL beakers (2)
-Weighing paper
-Antacids (2)
-Balance
-Buret
-Test tubes (2)
-Metal Stand
Assessment:
Verbal answers given during the informal group discussion and individual written
observations from the simulation on Day 1. Day 2 assessment will be the lab data and
answers to the worksheet questions.
Body of Lesson:
Day 1
Introduction:
0 min Set Context for Lesson (ENGAGE)
- Ask the students “What is an upset stomach? How do we treat it?”
-Today we will use a computer simulation to observe and analyze
what happens when you add an acid to a base and vice versa.
Content/Activity:
5 min Set Up Activity (EXPLORE)
-Using the computer, show the students where they need to go to find the
simulation. The web address is:
http://www.chem.iastate.edu/group/Greenbowe/sections/
projectfolder/flashfiles/stoichiometry/acid_base.html
-Show the students which variables need to be selected and how the
simulation works.
-Give instructions to the students. Hand out worksheet. Tell the students
to try different combinations of acids and bases and record their
observations, such as what happens to the pH when the acid or base is
added and what the graph looks like.
35 min Gather Students to Discuss Activity (EXPLAIN)
-What did you observe?
-Talk about and give definitions for titration, titrant, and standard solution.
-What happened to the pH as you added a strong acid or base? What
happened to the pH when you added a weak acid or base?
-What does the graph tell us? Why doesn’t the pH double when you add
twice as much base?
-Talk about the log basis of pH.
-Talk about end point, transition range, and buffering region.
-Talk about what the graphs for monoprotic, diprotic, and triprotic acids
should look like.
-Talk about what the graphs for weak and strong acids/bases should look
like.
Closure:
45 min Close
-Sum up key points. Students need to turn in their observation
worksheets (EVALUATE). Remind students that they will be doing a
titration lab tomorrow and that they need to read the lab write-up before
they come to class.
Day 2
Introduction:
0 min Set Context for Lesson
-Yesterday looked at a simulation where we added an acid to a base in a
titration.
-Today we are going to perform a titration.
-Give a brief overview of the lab activity: How Effective is Your Antacid?
(Source of Lab: http://www.filebox.vt.edu/users/mparker/Portfolio/
ChemistryTemplate/TitrationLab.pdf)
-Students can do the activity in pairs, which may be assigned.
Content/Activity:
5 min Perform the Experiment (ELABORATE)
-The students will follow the instructions to perform the experiment and
answer the lab questions.
-The students need to clean up their area and dispose of all materials in
the designated containers.
Closure:
45 min Close
-Student worksheets are due tomorrow. Everyone needs to turn in his or
her own sheet. (EVALUATION)
Adaptations:
-Make sure everyone has a computer on Day 1. If there are not enough computers,
assign partners.
-Make sure everyone has a partner on Day 2. If there are an odd number of students,
make one group of three.
Name ___________________________
Acid/Base Computer Simulation
Test a variety of combinations of acids and bases and record your observations,
including which acid and base you are testing. Do you see any patterns?
Name __________________________
How Effective is Your Antacid?
You probably have already used or seen someone use an antacid tablet (Tums is a popular brand)
to calm an upset stomach after eating. As part of our digestive process, our stomachs produce
hydrochloric acid (around pH of 2) to help break down foods. Sometimes, however, our
stomachs produce too much hydrochloric acid and this causes “acid indigestion”. Our throats and
tongue can sustain acid burns because they are not made of the same type of tissue found in the
stomach. In this lab, we will explore how antacids work and compare their effectiveness.
When hydrochloric acid is added to water, it donates a hydrogen cation (H+) to a water
molecule, producing a hydronium cation (H3O+) and an anion. A base is a substance that accepts
a proton (H+) donated by an acid. Antacids are bases. They are substances that are very good at
accepting protons (compared to water) and thus can reduce the amount of irritating acid (H+ or
H3O+) in your stomach. The hydroxide ion (OH-) is the most common base. Carbonate ion
(CO32- ) is also a common base used in antacids. When an acid and base react with each other, it
is called a neutralization reaction.
Safety:
Wear lab aprons, goggles, and gloves (if needed) at all times. Strong acids and bases are highly
corrosive and can damage skin and eyes. Remember to thoroughly wash your hands and
equipment when you have finished cleaning your lab station.
Data Table 1: Indicator Investigation
Color of HCl +
bromothymol blue
Color of NaOH +
bromothymol blue
Color after adding
HCl to NaOH
Number of drops it
took to turn NaOH
acidic
Initial
Volume
(mL)
Volume/
mass
(neutrali
zing
power)
Data Table 2: Antacid Titration
Antacid
Mass
Color
Color
Drops
before
after
NaOH
titration titration
Final
Volume
(mL)
Observations
Data Table 3: Class Data
Antacid
Brand
Active
Ingredient(s)
Trial 1
Trial 2
Trial 3
Average Neutralizing
Power
Procedure:
Indicator Investigation
1. Place 10 drops of 1 M HCl solution in a test tube, and place 10 drops of NaOH
solution in a different test tube.
2. Add 1 drop of bromothymol blue in each of the test tubes and swirl. If no color
change is present, add a second drop of bromothymol blue and swirl. Continue to
add only a single drop at a time (swirling after each drop) until a color change is
present. What do you observe? Record your observations.
3. Now, slowly drop HCl into the NaOH test tube one drop at a time. Gently stir the
solution to mix after each addition. Record your observations.
NOTE: Bromothymol blue is an indicator at a pH of 7
Antacid Titration
4. Obtain 2 antacid tablets your group is assigned to work with. Make sure you label
your samples – they will all look the same! Record the brands of antacids and the
active ingredient(s). Using a mortar and pestle, grind each tablet into a fine,
homogeneous powder.
5. Weigh approximately 1.0g of your first powdered tablet on weighing paper, recording
the exact mass. Pour the powder into a 100 mL beaker. Fill your beaker with 60 mL of
distilled water – mix well. Record your observations.
6. Add 15 drops of bromothymol blue indicator to your solution. Record the color.
7. Now, make sure the metal stand is firmly clamped to the lab bench, and be sure your
buret is firmly secured to the metal stand. Close your cockstop! (make sure the
cockstop is horizontal to the desk – if it is in a vertical line with the buret, your HCl will
run through!)
8. Place your squirt bottle of 1 M HCl at the top of the buret and carefully fill your buret
with 1 M HCl so it contains exactly 50 mL. (if you have more, place an empty container
under the stopcock and slowly open the valve – let the solution drip out until you have
the desired amount. Close the cockstop (make it completely horizontal to the table).
Record your initial volume.
9. Place your solution under the closed cockstop of the buret. Make sure you have your
glass stirring rod available. Slowly open the cockstop vale to allow only 1 drop at a time
fall from the buret. Keep track of the total number of drops added! One member should
carefully watch the drops and count, one member should continually stir, and the third
member should record the data. NOTE: If HCl initially begins to flow freely before you
can adjust it to single drops, have a group member note the initial volume and final
volume before the drops fall one by one. It takes approximately 20 drops for each mL,
so you can use this to estimate about how many drops fell!
10. When the color change becomes more permanent, stop titration when the color
change remains for at least 30 seconds and record your total number of drops and
final volume in the buret.
11. Calculate your neutralizing power by dividing number of drops / mass of antacid.
12. Carefully pour solution into the sink and rinse the beaker and stirring rod. After
you have dried it, obtain your second antacid sample and repeat steps 5-11.
13. When you have finished titrating your 2 antacid samples and recording all
information, promptly clean you stations taking care to thoroughly rinse all equipment
and wash your hands and lab station. DO NOT put soap in the buret!
14. Record your data on front board and copy data from other lab groups..
Results and Calculations
1. Is this neutralization reaction reversible? How do you know?
2. a. Categorize the antacids as monoprotic, diprotic, or triprotic.
b. What is the atomic mass of the cation in each antacid (e.g. Mg, Ca, etc.)?
c. Construct a bar graph that compares the neutralization power (drops/mass) of
each antacid – place the 4 antacids on the x-axis (labeled Antacids), and place
the neutralization power (drops/grams) on the y-axis.
d. Rank the antacids based on their neutralization power from the greatest to the
least. Is this ranking what you would expect? Use the information from (a) and
(b) to explain your answer.
Conclusions
1. What conclusion can you make about the bromothymol blue indicator in the
acid and base solutions?
2. Why is a substance that reacts with and dissolves in a strong acid but does not
dissolve in water a useful application - like an antacid for the stomach? (2-3
sentences)
3. Do the more effective antacids require more or less HCl to titrate compared to
the less effective brands? Use your data to explain how you know. (2-3
sentences)
4. On this basis, rank the effectiveness of the 4 brands of antacids in the order of
least effective to most effective.
5. Below is a price list of the antacids that were used in this lab. Which antacid appears
to be the best deal in terms of the amount of acid neutralized per dollar?
a. Rolaids, Extra Strength $1.44 for 30 tablets
b. Tums Ultra, Regular Strength $1.64 for 36 tablets
c. Maalox Max, Maximum Strength $3.43 for 35 tablets
d. Equate Antacid Tablets, Regular Strength $2.23 for 150 tablets