Conductimetric Titration and
Gravimetric Determination
of a Precipitate
In this experiment, you will monitor conductivity during the reaction between sulfuric acid,
H2SO4, and barium hydroxide, Ba(OH)2, in order to determine the equivalence point. From this
information, you can find the concentration of the Ba(OH)2 solution. The reaction between
sulfuric acid and barium hydroxide yields an insoluble product, barium sulfate, and water, as
shown in the reaction equation below.
Ba2+(aq) + 2 OH–
(aq) + 2 H+
(aq) + SO4
2–
(aq) → BaSO4(s) + 2 H2O(l)
In this reaction, the total number of dissociated ions in solution is reduced dramatically during
the reaction as a precipitate is formed. As 0.100 M H2SO4 is slowly added to Ba(OH)2 of
unknown concentration, changes in the conductivity of the solution will be monitored using a
Conductivity Probe. When the probe is placed in a solution that contains ions, and thus has the
ability to conduct electricity, an electrical circuit is completed across the electrodes that are
located on either side of the hole near the bottom of the probe body. This results in a
conductivity value that can be read by the interface. The unit of conductivity used in this
experiment is the microsiemens per cm, or µS/cm.
In addition, you will capture the precipitate, and measure its mass. You will have two methods,
therefore, of calculating the molar concentration of a barium hydroxide solution that is titrated
with a sulfuric acid solution of known concentration.
OBJECTIVES
In this experiment, you will
Measure the conductivity of the reaction between sulfuric acid and barium hydroxide.
Use conductivity values as a means of determining the equivalence point of the reaction.
Measure the mass of a product of the reaction as a means of determining the equivalence
point of the reaction gravimetrically.
Calculate the molar concentration of a barium hydroxide solution.
Figure 1 LabQuest 16
16 – 2 Advanced Chemistry with Vernier
MATERIALS
LabQuest magnetic stirrer
LabQuest App stirring bar or Microstirrer
Vernier Conductivity Probe two ring stands
barium hydroxide, Ba(OH)2, solution ring stand ring
0.100 M sulfuric acid, H2SO4, solution utility clamp
distilled water filter paper
two 250 mL beakers filter funnel
50 mL graduated cylinder balance, ±0.01 gram accuracy (or better)
10 mL pipet and pipet bulb or pump drying oven (optional)
Vernier Drop Counter 100 mL beaker
60 mL reagent reservoir
10 mL graduated cylinder
PROCEDURE
1. Obtain and wear goggles.
2. Use a pipet bulb (or pipet pump) to transfer 10.0 mL of the Ba(OH)2 solution into a 250 mL
beaker. Add 50 mL of distilled water. CAUTION: The barium hydroxide solution is caustic.
Avoid spilling it on your skin or clothing.
Figure 2
3. Set up the Conductivity Probe and Drop Counter.
a. Set the selector switch on the side of the Conductivity Probe to the 0–20000 µS/cm range
and connect the Conductivity Probe to LabQuest.
b. Lower the Drop Counter onto a ring stand and connect it to DIG 1.
c. Choose New from the File menu. If you have older sensors that do not auto-ID, manually
set up your sensors.
Conductimetric Titration and Gravimetric Determination of a Precipitate
Advanced Chemistry with Vernier 16 – 3
4. Obtain the plastic 60 mL reagent reservoir. Close both valves by turning the handles to a
horizontal position. Follow the steps below to set up the reagent reservoir for the titration.
a. CAUTION: H2SO4
is a strong acid, and should be handled with care. Rinse the reagent
reservoir with a few mL of the 0.100 M H2SO4 solution and pour the H2SO4 into an empty
250 mL beaker.
b. Use a utility clamp to attach the reservoir to the ring stand.
c. Fill the reagent reservoir with slightly more than 60 mL of the 0.100 M H2SO4 solution.
d. Place the 250 mL beaker, which contains the rinse H2SO4, beneath the tip of the reservoir.
e. Drain a small amount of the H2SO4 solution into the 250 mL beaker so that it fills the
reservoir’s tip. To do this, turn both valve handles to the vertical position for a moment,
then turn them both back to horizontal.
f. Discard the drained H2SO4 solution in the 250 mL beaker as directed.
5. Calibrate the Drop Counter so that a precise volume of titrant is recorded in units of
milliliters.
a. Choose Calibrate from the Sensors menu and select Drop Counter.
b. If you have previously calibrated the drop size of your reagent reservoir and want to
continue with the same drop size, select Equation. Enter the values for the New Slope and
the New Intercept. Select OK and proceed directly to Step 6.
c. If you want to perform a new calibration, select Start and continue with this step.
d. Place a 10 mL graduated cylinder directly below the slot on the Drop Counter, lining it up
with the tip of the reagent reservoir.
e. Open the bottom valve on the reagent reservoir (vertical). Keep the top valve closed
(horizontal).
f. Slowly open the top valve of the reagent reservoir so that drops are released at a slow rate
(~1 drop every two seconds). You should see the drops being counted on the screen.
g. When the volume of H2SO4 solution in the graduated cylinder is between 9 and 10 mL,
close the bottom valve of the reagent reservoir.
h. Enter the precise volume of H2SO4 and select Stop. Record the number of drops/mL for
possible future use and select OK.
i. Discard the H2SO4 solution in the graduated cylinder as indicated by your instructor and
set the graduated cylinder aside.
6. Assemble the apparatus.
a. Place the magnetic stirrer on the base of the ring stand.
b. Insert the Conductivity Probe through the large hole in the Drop Counter.
c. Attach the Microstirrer to the bottom of the pH Sensor. Rotate the paddle wheel of the
Microstirrer, and make sure that it does not touch the bottom of the Conductivity Probe.
d. Adjust the positions of the Drop Counter and reagent reservoir so they are both lined up
with the center of the magnetic stirrer.
e. Lift up the Conductivity Probe, and slide the beaker containing the Ba(OH)2 solution onto
the magnetic stirrer. Lower the Conductivity Probe into the beaker.
f. Adjust the position of the Drop Counter so that the Microstirrer on the Conductivity Probe
is just touching the bottom of the beaker.
g. Adjust the reagent reservoir so its tip is just above the Drop Counter slot.
h. Turn on the magnetic stirrer so that the Microstirrer is stirring at a fast rate.
7. You are now ready to perform the titration. LabQuest 16
16 – 4 Advanced Chemistry with Vernier
a. Start data collection. No data will be collected until the first drop goes through the Drop
Counter slot.
b. Fully open the bottom valve. The top valve should still be adjusted so drops are released at
a rate of about 1 drop every 2 seconds. When the first drop passes through the Drop
Counter slot, check the graph to see that the first data pair was recorded.
c. Observe that the conductivity readings decrease gradually. Continue watching your graph
to see when the conductivity begins to increase; this will be the equivalence point of the
reaction. When this increase in conductivity occurs, let the titration proceed for several
more milliliters of titrant.
d. Stop data collection to view a graph of conductivity vs. volume.
e. Turn the bottom valve of the reagent reservoir to a closed (horizontal) position.
8. Examine the data on the displayed graph to find the equivalence point; that is, the volume
when the conductivity value reaches a minimum. To examine the data pairs on the displayed
graph, select any data point. Record the H2SO4 volume, at the point of minimum
conductivity, in your data table.
9. Filter and measure the mass of the barium sulfate precipitate.
a. Use a hot plate to warm the beaker of mixture containing the BaSO4 precipitate. Warm the
solution to near boiling for about five minutes to help flocculate the particles.
b. While the mixture is heating, set up a ring stand and ring for the filter funnel. Measure and
record the mass of a piece of fine-grade filter paper and set the paper in the funnel.
c. Allow the mixture to cool, and then filter it. The liquid need not be at room temperature to
be filtered. Wash the precipitate out of the beaker with small amounts of distilled water, if
necessary.
d. Dry the precipitate and filter paper in a drying oven for at least 15 minutes.
e. Cool the precipitate and filter paper to near room temperature. Measure and record the
mass of the filter paper/precipitate.
f. Heat the precipitate again for five minutes, cool the precipitate, and weigh it.
g. Heat the precipitate a third time, for five more minutes, cool the precipitate and weigh it.
If the masses of filter paper/precipitate are the same in the final two weighings, dispose of
the filter paper as directed. If the final two weighings are not the same, check with your
instructor to see if more drying time is needed.
10. Rinse the Conductivity Probe with distilled water in preparation for the second titration.
11. Print the graph directly from LabQuest, if possible. Alternately, transfer the data to a
computer, using Logger Pro software.
12. Repeat the necessary steps to conduct a second titration. Conduct a third trial, if needed.
Record the results in the data table. Print the graph of your final trial. Conductimetric Titration and Gravimetric Determination of a Precipitate
Advanced Chemistry with Vernier 16 – 5
DATA TABLE
Trial 1 Trial 2 Trial 3
Equivalence point (mL)
Mass of filter paper + precipitate (g)
Mass of filter paper (g)
Mass of precipitate (g)
Molarity of H2SO4 (M)
DATA ANALYSIS
1. Use the titration results to calculate the moles of H2SO4 that were used to reach the
equivalence point in each trial.
2. Use your titration results to calculate the molar concentration (molarity) of the Ba(OH)2
solution using the molar amount of H2SO4 used in each trial.
3. Convert the mass of the barium sulfate precipitate, formed in each trial, to moles.
4. Use the moles of BaSO4 from 3 above to calculate the molarity of the Ba(OH)2 solution.
5. Compare the results of your calculations from 2 and 4 above with the actual molarity of the
Ba(OH)2 solution. Which method of analysis, equivalence point or gravimetric
determination, was more accurate in your experiment? Why? LabQuest 16
16 – 6 Advanced Chemistry with Vernier
KEY LEARNING POINTS
Electrolytic solutions
Titration
End point
Precipitation reaction
Stoichiometric calculation of a product
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