Changes to Experiment 4, Determination of Acid Constant, Ka
Chemistry 102 , Fall semester 2000
Los Angeles City College
4. Titration Curve: (You may wish to run through this part of the experiment in a fast
and dirty fashion for a first try just to get a feel for the apparatus, and to determine
what modifications need to be made. Then you could perform a second trial in
which you make the modifications --- and are very careful.)
a.
b.
c.
d.
e.
f.
g.
Weigh out a sample of unknown acid. The acid sample should probably
be somewhere between 0.3 and 0.5 grams. Use the same weighing
procedure you used in 2 (p. 76-77). Do not add an indicator. Dissolve
the unknown acid in about 100 mL distilled water.
Set up the apparatus as shown on the end island in room 112. You will
need to procure a clamp for the drop counter, a stop-watch, a buret and
buret clamp, a magnetic stirrer (with magnet bar) from the stock
room.The rest of the equipment is available at the four stations.
Open LabWorks. Calibrate the pH. (The pH of the buffer is 4.00.)
Click on Design, “Experiment Builder” and “Open an existing file”.
Open the “C” directory, open “LabWorks II 4.0” folder, Open
“Experiments” folder, Open either “New Folder” or “Succinic Acid
Titration Expt.”
Click on Acquire. Start the dropper. Start collecting data. When the
titration is complete, stop, and save data to data folder or to a floppy.
(Be sure to name your data, so it can be retrieved easily.)
Go to Analysis. From the graph and/or from the raw data you can
determine Ka.
In order to determine the equivalent weight of the unknown acid you
need to figure out how you can convert your graph from pH vs counts to
pH vs vol (NaOH). You may wish to devise a procedure that will give
you the appropriate data before you do your “real” trial. See me if
you need some suggestions.