Chemistry e-lab:
Acid-Base Titration
N. Jahng
Overview of the Activity
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Students will use the pH Sensor to
investigate the titration process. They will
use a titrant of a known concentration to
determine the concentration of a HCI
solution.
Learning Goals
Students will:
 Learn the relationship between pH and chemical
reactions.
 Learn how the titration process works.
 Understand how to use titration to determine
molarity.
 Observe the curve of a titration-inspect how pH
change is gradual on either side of the equivalence
point until very near it.
 Use the plot of pH versus volume to determine the
amount of sodium hydroxide solution needed to
neutralize the acid solution.
Vocabulary
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pH indicates whether a solution is acidic, basic (alkaline), or
neutral.
Titration is a quantitative measurement of an unknown solution
(called the analyte: the substance being analyzed) by reacting it
completely with a standardized reagent that is a solution of known
concentration (called the titrant).
Endpoint: the point when the indicator colour changes (usually the
end of the titration)
Eqivalence point in a titrantion process at which the amount of
titrant is chemically equivalent to the amount of material titrated (in
acid-base titrations equivalents refer to the number of moles of H+
and OH–)
Indicator: A compound having a physical property (usually color)
that changes abruptly near the equivalence point of a chemical
reaction.
Molarity is a description of the concentration of a solution,
expressed by the number of moles of solute per liter of solution.
Background
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Acids and bases react until one of the reactants is consumed
completely. A base solution of known concentration can
therefore be used to titrate an acid solution of unknown
concentration.
As a base solution (sodium hydroxide, NaOH) is added to an
acid solution (hydrochloric acid, HCI), ions from the base and
ions from the acid solution react chemically to form a neutral
product. As a result, the pH of the acid solution begins to
change.
The equivalence point is the point at which all the ions from
the acid solution are bonded to ions from the base solution.
The equivalence point of an acid-base titration can be detected
with a pH electrode.
YouTube video
Equipment & Materials
computer with USB port
0.10 M sodium hydroxide (NaOH),
100.0 mL
PASPORT USB interface
hydrochloric acid (HCl), unknown
concentration, 10.0 mL
PASPORT pH Sensor
protective gear
DataStudio software
wash bottle and waste container
Small Tripod Base & Rod
water, distilled, 500.0 mL
Buret Clamps, 2
beaker, 250-mL
buret, 50-mL
graduated cylinder, 100-mL
magnetic stirrer and stir bar
pipet with bulb, 10-mL
Computer Setup
1.
2.
Plug the USB interface into the computer’s USB
port.
Connect the pH electrode to the pH Sensor. Plug
the pH Sensor into the USB interface. This will
automatically launch the PASPORTAL window.
pH Sensor
USB interface
pH electrode
3. Choose the appropriate DataStudio
configuration file entitled 15 Titration
CF.ds. and proceed with the following
instructions.
• Note: Configuration files automatically
launch the appropriate display(s), sampling
rate(s). etc.
Equipment Setup
Rinse and fill the buret with 0.10 M
sodium hydroxide solution
10.0 mL of the hydrochloric acid solution
pH electrode
100.0 mL of distilled water
magnetic stirrer
Titration Technique using a buret
1.
2.
3.
4.
5.
6.
Measure 100.0 mL of distilled water into a clean, dry 250-mL
beaker.
Use a pipet to add 10.0 mL of the hydrochloric acid solution
into the beaker with the distilled water. Record the volume of
hydrochloric acid in Table 1.
Carefully add a spin bar to the beaker. Place the beaker on
the magnetic stirrer.
Position the pH electrode in contact with the acid solution.
Rinse the 50-mL buret with a few milliliters of the 0.10 M
sodium hydroxide solution. Fill the buret with 0.10 M sodium
hydroxide solution. Be sure to start the titration with the
buret filled exactly to the 0.00 mL mark. Record the precise
concentration of the sodium hydroxide solution in Table 1.
Turn on the magnetic stirrer.
Experiment procedures
Record Data
1. Arrange the displays to see the table of “pH and Volume”.
2. Click the Start button to begin recording data. The Start
button changes to a Keep button.
• Note: Do not add any NaOH titrant for the first reading.
3. When the pH value stabilizes, click Keep. Click the Tab key to
move to the next row in the Table.
4. The Table display shows the first 'pH, Volume' pair in the first
row.
5. Open the buret's valve and add some of the sodium hydroxide.
Add enough titrant to raise the pH by about 0.15 units, and
then close the valve.
6. After the titrant has been added and the pH reading stabilizes,
type the total volume of sodium hydroxide added into the next
row in the table and then click Keep.
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Note: To read the volume, measure at the bottom of the meniscus of
the sodium hydroxide solution in the buret.
6. After the titrant has been added and
the pH reading stabilizes, type the
total volume of sodium hydroxide
added into the next row in the table
and then click Keep.
• Note: To read the volume, measure at the
bottom of the meniscus of the sodium
hydroxide solution in the buret.
7. Continue adding sodium hydroxide solution in amounts that
raise the pH by about 0.15 units. Each time type in the total
amount of sodium hydroxide added.
8. When pH 3.5 is reached, change to 2-drop increments.
Continue to type in the total volume of sodium hydroxide
added after each increment.
9. After pH 10.5 is reached, again add larger increments of
sodium hydroxide (enough to raise the pH by about 0.15
units) and type in the total volume of sodium hydroxide
added.
10. Continue adding sodium hydroxide until the pH stops
changing. Click the Stop button to end data recording.
11. Turn off the magnetic stirrer. Remove the pH Sensor
from the solution. Rinse the pH Sensor in distilled water
and dry the sensor gently.
12. Dispose of the solution in the beaker as instructed.
13. If time permits, repeat the procedure.
14. Save your DataStudio file as your group members’ name
to the location of Document>EDCP447>Chemistry
folder.
Analyze
Write a lab report using the Workbook in the Data Studio.
1. Insert your graph of pH versus Volume.
2. In your graph of pH versus Volume, use the Smart Tool to find the volume
of titrant (sodium hydroxide solution) just before, just after, and at the
equivalence point. Record your results in Table 1.
3-1. Use the values from Table 1, calculate the number of moles of NaOH
used. Record the number in Table 2.
3-2. Move the Smart Tool cursor to the point on the plot where the pH is 7.0
(or as close as possible). Record the x-coordinate as the "NaOH volume
added at the equivalence point” in Table 2.
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4-1. Use the equation for the neutralization
reaction to calculate the number of moles of
HCl used. Record the number in Table 2.
4-2. The average of the volume of NaOH just
before and just after the largest pH increase
should be very close to the volume of NaOH
added at pH = 7.
Table 1
Item
Volume of HCl
Concentration of NaOH
NaOH volume added before largest pH
increase
NaOH volume added after largest pH
increase
Average of NaOH before and after pH
increase
Value
Table 2
Item
NaOH volume added at equivalence point
Moles of NaOH
Moles of HCl
Volume of HCl
Concentration of HCl
Value