Name:______________________________
Date:_____________
CH105
Pre-Lab 6: Acid-Base Titration
Directions: Read the Goals, Background, Safety, and Procedure sections for this
experiment, then answer the following questions in the space provided. For calculation
questions, show all work and report answers in a box with the appropriate significant
figures and units. Pencil is acceptable for this assignment.
1. How many moles of NaOH are in a 18.3 mL sample of 1.581 M NaOH?
2. How many moles of HCl are in a 25.00 mL sample that is neutralized with
18.3 mL of 1.581 M NaOH? (Hint: Extra information is given in this question.)
3. What is the molarity of a 25.00 mL HCl solution that is neutralized by
18.3 mL of 1.581 M NaOH?
4. If 28.3 mL of 0.2321 M HCl neutralize a 0.500 g antacid tablet containing
CaCO3, how many grams of CaCO3 are in the tablet? (Hint: Extra information
is given in this question.)
5. A 0.500 g antacid tablet containing CaCO3 is neutralized by 28.3 mL of
0.2321 M HCl. If the manufacturer claims that 0.350 g of CaCO3 are in
each tablet, what is the percent difference between your calculated value of
CaCO3 (from question 4) and the manufacturer’s claim?
1
Experiment 6:
Acid-Base Titration
Goals: •
•
•
•
•
Complete several acid-base titrations.
Reach the endpoint of a titration.
Check level of precision for multiple trials.
Perform a reaction between an antacid tablet and HCl.
By titration, determine the moles of excess acid remaining after the
antacid tablet reacts.
• Calculate the grams of active ingredient and inert binders in an
antacid tablet.
• Calculate a percent difference.
Purpose: Perform multiple titrations to determine the concentration of an
unknown HCl solution and the amount of active ingredient in an
antacid tablet.
Background:
A titration is a quantitative laboratory technique that is used to determine the
concentration of an unknown solution from a standard solution. Many types of
titration can be performed; however, the most commonly performed titration in
General Chemistry labs are acid-base titrations.
An acid-base titration can be performed with any acid and base combination.
For simplicity, you will perform a strong acid-strong base titration. This
reaction does not involve an equilibrium equation (which as you know tend to
complicate reactions!).
The general equation for an acid-base reaction is:
acid + base → salt + water
This is a neutralization reaction when stoichiometric amounts of acid and base
are added. If the amounts are stoichiometric, no acid or base will remain as an
excess reactant.
For today’s reaction, you will have a known
concentration of sodium hydroxide as your base.
This sodium hydroxide will be placed in a long,
slender piece of glassware called a buret. The
buret you will use in this lab will be graduated
into 50 mL with every tenth of a milliliter
marked. Every time you read the buret, you will
need to read the volume to the nearest 0.01 mL.
You will guesstimate the last digit based on the
position of the bottom of the meniscus. The
0.00 mL mark is at the top of the buret and the
50.00 mL mark is at the bottom of the buret.
The example buret on the right only has
individual milliliters marked, so the buret
reading would be 29.2 mL. (Your buret in lab will
have a higher level of precision than this drawing!)
2
Close-up:
50-mL buret
Acid-Base Titration • 3
The liquid leaves the buret once you open the stopcock. The stopcock is located
at the bottom of the buret and may be made of glass or plastic. It is important
that the stopcock fit snuggly in order to prevent leakage. The stopcock is closed
when the finger grips are perpendicular to the buret and open when the finger
grips are parallel to the buret. Your instructor will demonstrate proper buret
usage during the Pre-Lab lecture.
Your first unknown in today’s lab is hydrochloric acid. In order to determine
the concentration of the hydrochloric acid, you will obtain an exact amount of
HCl using a pipette. You will use a total delivered pipette. When you fill the
pipette, you will allow as much liquid as possible to flow out of the pipette. A
small amount of liquid will be trapped in the pipette. Do not force the liquid
out of the pipette!
Once your buret is filled with standard base and the appropriate amount of
unknown HCl has been placed into an Erlenmeyer flask, you will need to add
phenolphthalein indicator to the acid. As you recall, an indicator is a chemical
material that will change color at a specific pH. In acid, the phenolphthalein
will appear colorless; however, in a basic solution, the phenolphthalein will
appear pink.
As you perform this titration, you will allow base to flow
from the buret into your Erlenmeyer flask. It is
recommended that you swirl the flask over a piece of white
paper in order to see the color of the solution. At the
point that the solution in the flask becomes a pale shade
of pink and keeps the color for at least 1 minute, you have
reached the endpoint of the titration. The endpoint is the
point in a titration where the moles of acid and the moles
of base are equal.
Standard
NaOH in
the buret
Your titration will involve hydrochloric acid and sodium
hydroxide.
HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)
At the endpoint the moles of HCl equal the moles of NaOH.
The indicator phenolphathalein was chosen for this
experiment because its color change occurs at this
endpoint.
You will repeat this titration at least 2 more times, and
then perform a titration to determine the amount of the
active ingredient is in an antacid tablet.
For the antacid tablet reaction, you will first react the
antacid with a new sample of the unknown HCl solution.
This is the same unknown you used in the first part of the
lab and at this point you will know the concentration of
this “unknown” HCl solution.
10.00
mL
unknown
HCl
+ 2 drops
phenolphathalein
Titration Setup.
4 • Experiment 6
The reaction will likely be:
CaCO3 (aq) + 2 HCl (aq) → CaCl2 (aq) + H2O (l) + CO2 (g)
Check the antacid container to see what the active ingredient for your tablet is.
Write a balanced equation for the reaction between the active ingredient and
HCl.
CO2
(g)
antacid
tablet +
50.00 mL
HCl
Titrate
excess acid
excess
HCl +
H2O (l) +
CaCl2 (aq)
Once you have reacted the tablet, all of the active ingredient should have
reacted because it is the limiting reactant. The experiment is designed so that
some hydrochloric acid will remain because it is the excess reactant.
Consequently, you will be able to titrate your excess acid to determine the
moles of acid remaining in your flask.
Calculation hints:
Moles of acid added to antacid tablet  Volume of unknown acid used  Concentration of unknown acid (M)
Moles Acid
Balanced Equation 
Moles Base
Moles of Excess Acid  Moles of Acid Titrated by Base 
Moles of Excess Acid  Volume of Base  Molarity of Base 
That value, coupled with the moles of acid initially in the flask, will allow you to
calculate:
(1) the amount of acid used to neutralize the antacid tablet,
Moles of acid r eacted with tablet  Moles of acid added to antacid tablet  Moles of acid titrated by base
(2) the amount of active ingredient in the antacid tablet, and
Moles Antacid
(Balanced equation)
Moles Acid
Grams of antacid in tablet  Moles of antacid in tablet  MM antacid
Moles of antacid in tablet  Moles of acid r e acted with tablet 
(3) the amount of inactive binders in the antacid tablet.
Grams of binder in tablet  Mass of tablet (g)  Grams of antacid in tablet
Acid-Base Titration • 5
You will also calculate the percent difference between the manufacturer’s
reported amount and the experimentally measured amount of active ingredient
in the tablet.
Percent difference is an excellent way to compare a theoretical value and an
experimental value.
% difference 
exp erimental  theoretica l
theoretica l
 100%
Procedure: All waste generated today should be poured into the
“Acid/Base Waste” container.
Titration of an unknown acid
1. Obtain a buret from the buret drawer in the back of the classroom.
2. Check the buret to make sure the stopcock and tip are secure. Make
adjustments as necessary.
3. Rinse the buret with tap water twice. Make sure all of the inside surfaces
are rinsed.
4. Rinse the buret with distilled water three times. Make sure all of the inside
surfaces are rinsed.
5. Pour 100 mL of the standard base into a clean, dry 250 mL beaker.
6. Make sure the stopcock on the buret is closed.
7. Pour 5-10 mL of the standard base into the buret. Carefully make sure that
all of the surfaces within the buret are rinsed with the standard base.
8. Open the stopcock and allow the base to flow into a labeled waste beaker.
9. Close the stopcock. Pour enough standard base into the buret that the base
level is above the 0.00 mL mark.
10. Open the stopcock enough to fill the buret tip with standard base. (Place
the waste beaker under the buret.) Make sure no bubbles are left in the
buret tip.
11. Look at the level of the standard base in the buret. If the meniscus is still
above the 0.00 mL mark, open the stopcock and allow the level to at least
reach the 0.00 mL mark. Once the meniscus is at or below the 0.00 mL
mark, record the buret reading on your data sheet under “initial buret
reading for trial 1.”
12. Pour 100 mL of an unknown acid into a clean, dry 250 mL beaker. Write
down the unknown letter of the acid on your data sheet.
6 • Experiment 6
13. Rinse a 10 mL pipette with tap water twice and distilled water once. Draw a
small amount of the unknown acid into the pipette and rinse the inside of
the pipette with the acid. Use this 10 mL pipette to measure exactly 10.00
mL of the unknown acid.
14. Release the unknown acid into a clean, dry 250 mL Erlenmeyer flask. Add 2
drops of phenolphthalein indicator.
15. Make sure the initial buret reading is recorded on your data sheet.
16. Perform a quick titration. Place a piece of white paper under the Erlenmeyer
flask. Move the paper and the flask under the buret. Open the stopcock,
swirl the Erlenmeyer flask, and watch for the solution in the flask to begin
to turn color. When a pinkish spot begins to form where the base is
draining into the flask, slightly close the stopcock in order to slow the flow of
base. Ideally, you will close the stopcock at the point when the solution
turns and stays a very light pink color. This is the point at which the
concentration of acid and the concentration of base are exactly equal.
Record the final volume reading in the buret.
17. Calculate the total volume of base used to titrate the unknown acid.
18. Keep the first Erlenmeyer flask as a reminder of the approximate color
desired in a titration.
19. Use the 10 mL pipette to measure exactly 10.00 mL of the unknown acid.
Release the unknown acid into another clean, dry 250 mL Erlenmeyer flask.
Add 2 drops of phenolphthalein indicator.
20. Look at your buret. Does enough standard base remain to titrate 10 mL of
unknown acid? If not, you may choose to add base to your buret at this
point or you will add base during your titration. No problems will arise from
adding base to the buret during your titration, but it is very important that
the base level NEVER go below the 50 mL mark during your titration!
As the level approaches the 50 mL mark, stop the titration, record a final
buret reading on your data sheet, add more base to the buret, record a
second “initial buret reading” for the titration, finish the titration, and record
a second “final buret reading.” The goal in performing a titration is to know
the total volume of standard base added to the Erlenmeyer flask.
21. Record your initial buret reading on your data sheet for trial 2. Place your
Erlenmeyer flask and white paper under the buret and begin your titration.
Perform this titration in a more controlled manner. The first titration gave
you an indication of approximately how much volume will be required to
change the color of the solution. Use this as a guideline. It is very likely
that you could add 5 mL less than the total volume reading from trial 1 to
the Erlenmeyer flask and no color change would occur. This could be done
quickly and then the last little bit could be added more slowly. The last drop
can be added by quickly turning the stopcock from a closed position 180˚ to
the opposite closed position.
Acid-Base Titration • 7
22. Record the final buret reading on your data sheet for trial 2 and calculate
the total volume of base used in the second trial.
23. Repeat steps 19-22 for a third trial. If your volumes are not within 5% of
each other for trials 2 and 3, perform a fourth trial.
24. Calculate the concentration of the unknown acid.
Titration of Antacid Tablets
1. Mass a piece of weighing paper and record this value on your data sheet.
2.
Add an antacid tablet to the weighing paper, mass the antacid tablet and the
weighing paper, and record this value on your data sheet.
3.
Look at the antacid package and record the name and mass of the active
ingredient per tablet on your data sheet.
4. Transfer the tablet to a clean, dry 250 mL Erlenmeyer flask.
5. Rinse a 50 mL pipette with tap water twice and distilled water once. Draw a
small amount of the unknown acid into the pipette and rinse the inside of
the pipette with the acid. Use this 50 mL pipette to measure exactly 50.00
mL of the unknown acid.
6. Put 50.00 mL of the unknown acid into the flask that contains the tablet.
7. Heat the flask to boiling on a hot plate. Gently boil the solution for about 5
minutes. Use a glass stirring rod, if necessary, and GENTLY help break up
and disperse the tablet.
8. Refill your base buret with the standard base. Record the initial buret
reading on your data sheet.
9. Cool the antacid solution to room temperature by immersing it in a
container of tap water. Use a hot pad or gloves to avoid burns.
10. When the solution has cooled, add 2 drops of phenolphthalein to the
solution.
11. Titrate the solution. The volume of base needed will probably be different
from the other titrations you have performed.
12. Record the final buret reading on your data sheet and calculate the total
volume of standard base used.
13. Calculate the moles of excess acid that was titrated by the standard base
and the moles of acid that reacted with the antacid tablet.
14. From your laboratory data, calculate the moles of active ingredient in the
antacid tablet that reacted with the acid.
8 • Experiment 6
15. Calculate the grams of active ingredient in the antacid tablet that reacted
with the acid.
16. Calculate the percent difference between the mass of active ingredient in
each tablet that you calculated and the mass of active ingredient reported by
the manufacturer.
17. Subtract the grams of active ingredient in the tablet from the mass of the
tablet to determine the mass of the inert binders used in making the tablet.
18. Calculate the mass percent of inert binder in the antacid tablet.
19. Repeat this titration with a second tablet, if time allows. Share data marked
with an asterisk (Mass of weighing paper, Mass of weighing paper + tablet,
and Initial and Final Buret Readings) with another group that used the
same unknown acid.
Name:______________________________
Date:_____________
CH105
Data Sheet 8: Acid-Base Titration
Directions: Record the data as it is collected onto this sheet in BLUE or BLACK ink. Do
not use white out. Correct mistakes by making a single line through the error and
writing the new information above or beside the mistake.
Standard Base Information
Identity ____NaOH__________
Concentration _______________________
Unknown Acid Information
Identity ____HCl__________
Unknown Letter _____________________
Balanced equation for the reaction between standard base & unknown acid
NaOH (aq)
+
HCl (aq) 
Volume of unknown acid used (mL)
Trial 1
Trial 2
Trial 3
Trial 4
10.00
10.00
10.00
10.00
Initial buret reading (mL)
Final buret reading (mL)
This is only
used if you
refill your
buret in the
middle of a
titration.
Second initial buret reading (mL)
Second final buret reading (mL)
Total volume of base used (mL)
Concentration of unknown acid (M)
Average Acid Concentration from
Trials 2 & 3 (M)
% difference 
Trial 3  Trial 2
Average of Trials 2 & 3
 100%
Percent difference between trial 2 and trial 3___________________________________
Antacid information
Name of antacid _____________________________
Name of active ingredient _____________________________________________________
Amount of Active Ingredient per Tablet ________________________________________
Balanced equation for the reaction between active ingredient & acid
HCl (aq) +

9
Experiment 6
Data Sheet
Trial 1
Trial 2
Trial 3
Trial 4
*Mass of weighing paper (g)
*Mass of weighing paper + tablet (g)
Mass of tablet (g)
Volume of unknown acid used (mL)
50.00 mL
Concentration of unknown acid (M)
Moles of acid added to antacid tablet
*Initial buret reading (mL)
*Final buret reading (mL)
This is only
used if you refill
your buret in
the middle of a
titration!
*Second initial buret reading (mL)
*Second final buret reading (mL)
Total volume of base used (mL)
Moles of acid titrated by base
Moles of acid reacted with tablet
Moles of antacid in tablet
Grams of antacid in tablet
Percent difference of active ingredient calculated in
tablet versus manufacture claims
Grams of binder in tablet
Mass percent of binder in tablet
* Data that can be shared is marked with an asterisk! Calculations should be
performed on your own!
10
Name:______________________________
Date:_____________
CH105
Post Lab 8: Acid-Base Titration
Directions: Answer the following questions in the space provided. For short answer
questions, write complete sentences and provide a reason for the answer. For
calculation questions, show all work and report answers in a box with the appropriate
significant figures and units. Pencil is acceptable for this assignment.
1. Write a balanced equation for the reaction between sulfuric acid (H 2SO4) and
sodium hydroxide.
2. Potassium hydrogen phthalate (also known as KHP), KHC8H4O4, is
frequently used as the neutralization standard for sodium hydroxide. What
mass of KHP will react with 25.00 mL of 1.654 M NaOH?
2 KHC8H4O4 (aq) + 2 NaOH (aq) → 2 H2O + Na2C8H4O4 + K2C8H4O4
3. What volume in milliliters of 1.654 M NaOH will react with 15.00 mL of
2.84 M HCl?
4. A 1.654 M NaOH solution is placed in a buret and reacted with 15.00 mL of
2.84 M HCl. If the initial volume reading is 12.84 mL, what will the final
volume reading be? (Hint: The answer from 3 can be used to help answer this question.)
5. If HCl is placed in the buret and NaOH is mixed with phenolphthalein in the
Erlenmeyer flask, how will the titration differ from the one you performed in the
laboratory?
11