A titration is a process used to determine the volume of a solution needed to react with a
given amount of another substance. In this experiment, you will titrate hydrochloric acid
solution, HCI, with a basic sodium hydroxide solution, NaOH. The concentration of the
NaOH solution is given and you will determine the unknown concentration of the HCI.
Hydrogen ions from the HCI react with hydroxide ions from the NaOH in a one-to-one ratio
to produce water in the overall reaction:
When an HCI solution is titrated with an NaOH solution, the pH of the acidic solution is
initially low. As base is added, the change in pH is quite gradual until close to the
equivalence point, when equimolar amounts of acid and base have been mixed. Near the
equivalence point, the pH increases very rapidly, as shown in Figure 1. The change in pH
then becomes more gradual again, before leveling off with the addition of excess base.
In this experiment, you will use a computer to monitor pH as you titrate. The region of
most rapid pH change will then be used to determine the equivalence point. The volume
of NaOH titrant used at the equivalence point will be used to determine the molarity
Volume NaOH (mL)
Use a pH Sensor to monitor changes in pH as sodium hydroxide solution is added to a
hydrochloric acid solution.
Plot a graph of pH vs. volume of sodium hydroxide solution added.
Use the graph to determine the equivalence point of the titration.
Use the results to calculate the concentration of the hydrochloric acid solution.
magnetic stirrer (if available)
~0.1 M NaOH solution
1 utility clamp
50 mL buret
10 mL pipet
250 mL beaker
2nd 250 mL beaker
2nd utility clamp
1. Obtain and wear goggles.
2. Add 50 mL of distilled water to a 250 mL beaker. Use a pipet bulb to pipet 10.0 mL of
the HCI solution into the distilled water in the 250 mL beaker. CAUTION: Handle the
hydrochloric acid with care. It can cause painful burns if it touches the skin.
3. Place the beaker on a magnetic stirrer and add a stirring bar.
4. Use a utility clamp to suspend a pH Sensor on a ring stand as shown here. Position the
pH Sensor in the HCI solution and adjust its position so it will not be struck by the
bar. Turn on the magnetic stirrer, and adjust it to a medium stirring rate
splashing of solution).
5. Obtain approximately 60 mL of ~0.1 M NaOH solution in a 250 mL beaker. Obtain a 50
mL buret and rinse the buret with a few mL of the ~0.1 M NaOH solution. Use
clamp to attach the buret to the ring stand as shown here. Fill the buret a little above
the 0.00 mL level of the buret with ~0.1 M NaOH solution. Drain a small amount of
NaOH solution into the beaker so it fills the buret tip and leaves the NaOH at the 0.00
mL level of the buret. Record the precise concentration of the NaOH solution
data table. Dispose of the waste solution from this step as directed by your
CAUTION: Sodium hydroxide solution is caustic. Avoid spilling it on your skin or clothing.
adding NaOH solution in increments that raise the pH by about 0.15 units and
enter the buret reading after each increment. Proceed in this manner until the pH is
7. When a pH value of approximately 3.5 is reached, change to a one-drop increment.
Enter a new buret reading after each increment. Note: It is important that all increment
volumes in this part of the titration be equal; that is, one-drop increments.
8. After a pH value of approximately 10 is reached, again add larger increments
the pH by about 0.15 pH units, and enter the buret level after each increment.
9. Continue adding NaOH solution until the pH value remains constant.
Concentration of NaOH
NaOH volume added before the largest pH
NaOH volume added after the largest pH increase
Use the information in the data table above, determine and fill in the box below:
Volume of NaOH added at equivalence point
(Hint: average of NaOH volume before and after
largest pH change)
Moles NaOH (Hint: Use molarity equation to
determine the mole of NaOH, molarity and
volume of NaOH at equivalence points are in the
Moles HCI (Hint: stoichiometric ratio of HCI and
NaOH is 1 to 1)
Molarity of HCI (Hint: volume of HCI used in this
experiment is 10 mL)
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