This is a Titration Lab question. Here are some experimental
data:
25 mL of Weak acid
25 mL of Water added to flask
M of NaOH 0.102 M
Trial 1 eq point
dpH/dvol
avg vol(mL)
12.6
26.25
Trial 2 eq point
dpH/dvol
avg vol(mL)
12.07143
25.65
Procedure:
Obtain ~30 mL of your unknown acid and ~50 mL of the NaOH(aq) in
appropriately sized, labeled beakers. Fill the burette with the
NaOH solution to exactly 0.00 mL.
Setup the LabQuest2 interface system by plugging the pH
electrode into a port on the LabQuest2. CARE! These are very
delicate, sensitive, and expensive instruments. When moving the
electrode between solutions it should be rinsed with D.I. water and
the outside carefully dried with kim wipes.
Turn on the LabQuest2 interface, and it should auto detect the
pH electrode sensor and it will provide a Time versus pH
experiment. For this experiment, we wish to record pH as a function
of titrant volume, so you'll need to change the default
settings.
To set up your experiment, click on the “Mode” menu and change
it to “Events with Entry”, then name your column “Volume of
Titrant”. Change the “Units” to “mL”. After you have done that,
click the “Done” button.
Pipet 25.00 mL of the unknown acid solution into a 100 or 150 mL
beaker. Pipet another 25.00 mL of water into the beaker.
Place a small stirrer bar into the acid and place the beaker
onto a stirrer plate. Position the pH meter in the solution and the
burette (containing the NaOH(aq)) above the beaker. Make sure that
the solution can be stirred without the stirrer bar crashing into
the pH probe, and without excessive splashing. During the
experiment you need only control the stopcock of the burette if you
have set everything up carefully.
When you are ready to begin collecting data, simply click the
“Collect” icon at the bottom-left corner of your screen. The icon
will change to a red square “Stop” icon.
As the experiment starts you will see the pH of your solution
displayed. Collect a pH reading when these become stable by
clicking on “Keep” next to the “Collect” icon. A window will open
asking you the volume of titrant added. Enter the initial volume on
your buret. You should estimate the burette readings to at least
the nearest 0.05 mL.
Begin adding the NaOH from the burette. As a rough guide, you
should add a quantity of NaOH to bring about a change of
approximately 0.2 pH units. This will require adding the NaOH drop
by drop from the burette when you near the equivalence point. Allow
the pH reading to stabilize and click “Keep” to record the value.
Enter the volume on your buret. Repeat as many times as
necessary.
End the titration about 5 mL NaOH past the equivalence point.
Click the “Stop” icon once you have collected all the data you
need.
Discard the solutions in the appropriate waste vessel, and
repeat the above procedure to generate a second set of data if
necessary. Make sure to save your data before starting
over.
Repeat all steps 1 -11 above except use one of the unknown base
solutions as the titrand and the standardized HCl solution as the
titrant.
Questions:
Based on your experimentally observed equivalence point,
calculate the original concentration of your unknown acid and your
unknown base that came from the stockroom.
Based on your experimentally observed half equivalence
points, calculate the Ka of unknown acid.and the Kb of the unknown
base.
Compare the calculated Ka to literature values of formic
and acetic acid and determine the identity of your unknown
acid. Compare the calculated Kb to literature values of
ethylamine and benzylamine and determine the identity of your
unknown base.
Based on your answers to 1 & 2, calculate the
expected pHs at the equivalence point and compare this to your
experimentally determined values.