Peer Review

Titration Applet

Material Detail page

Reviewed:: May 4, 2005 by Chemistry

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Ratings

Overall Rating:

Content Quality:

Effectiveness:

Ease of Use:

Overview:: A series of amino acids are specified as unknowns. The pK values for these
acids are also given in the table. One of these is selected as an unknown. The
student specifies an amount of unknown and a volume of solution into which to
dissolve the unknown. The pH of the starting solution is then given. The
student then selects a titrant and volume of titrant to add. Selective aliquots
result in a newly calculated pH and the appearance point by point of a
titration curve.
Type of Material:: This site provides an applet detailing the pH of a solution resulting from the
titration of an amino acid. The applet is a highly interactive simulation,
providing experience with titration as an analytical and qualitative analysis
tool.
Recommended Uses:: This tool would be very effective for demonstrating how to calculate pK's of
acids from measurements and how to infer an unknown based on these values. It
would also be very useful in demonstrating when extra care is required in the
titration process. This may be used as a homework assignment after introducing
topic in lecture or as a prelab assignment.
Technical Requirements:: This applet requires a Java-enabled browser that supports Java 1.1. Netscape
Navigator 4.04 or later (with the JDK update for version 4.04) and Internet
Explorer 4.1 provide such support.
Identify Major Learning Goals:: The purpose of the activity is to simulate the titration of an unknown acid or
base and then identify the unknown compound from the pKa/s and molar mass
calculated from the titration data.
Target Student Population:: The students who would benefit most from this are second semester freshman
chemistry students and entry level biochemistry students.
Prerequisite Knowledge or Skills:: Students must know how to calculate the pKa of an acid from the titration curve
and should be familiar with calculations of concentrations of acid and conjugate
bases from pH values.

Content Quality

Rating:
Strengths:: The ability to carry out every part of a titration except for actually using the
chemicals provides terrific insight and practice for the student. The fact
that the acids have multiple pK values adds additional richness to the applet
use.
Concerns:: 1.A brief introduction of weak acid-base equilibria and pKa would be helpful as
would a brief description of the relationship between pKa nd the pH at the half
stoichiometric point.
2. All the unkowns are amino acids presenting a more complicated analysis due to
the "zwitterion" possibility.
3. The table of unknowns gives pKa1, pKa2,etc but during several trials this
reviewer was not able to get titration data to allow calculation of the second
and third pKas.
4. Some of the unknowns have molar masses and pKas very close to one another,
making it very difficult to conclusively identify the unknown on the basis of
the data.
5. All of the solutions begin as acids so there is no practice with titrating a
base with an acid.

Potential Effectiveness as a Teaching Tool

Rating:
Strengths:: The simultaneous calculation of pH and graphing of same in response to student
determined aliquot addition gives the student excellent insight into the
titration process. Could be used as homework, prelab assignments or as a virtual
lab.
Concerns:: It would be very helpful if smooth curve fits were available as a simultaneous
display to guide the student towards a more exacting determination of
equivalence points from which the pK's are determined. Since this does not have
a good introductory narrative section, this should be assigned only after a good
introduction to titrimetric analysis, weak acid-base equilibria, and pH and pKa
concepts.

Ease of Use for Both Students and Faculty

Rating:
Strengths:: This is an excellent way for students to gain interactive experience with
titrations and pKa calculations etc. The simultaneous graph and pH calculations
are a potent combination. The module is well-designed in terms of adding
titrant, recording data, plotting titration curve and thereby allowing
calculation of molar mass and pKa. It is robust and is easy to enter and exit
from.
Concerns:: The graphing applet expansion and contraction icons on the top right hand corner
do not work.
There should be the possibility of using a smooth functional fit through the
data or other means so that the data can be turned into first and second
derivatives for more precise determination of pK's.
When the cursor is moved, it should follow the titration points (and fitting
curve) so that the data can be analyzed more thoroughly.
The plot should be larger and should be set up to appear at a location that
doesn't interfer with the data table or the aliquot addition size etc.
Even after several attempts it was not possible to obtain data on second and
third pKas although that was offered as a possible objective.

Other Issues and Comments:: This is a good module whose use can be improved by adding introductory text and

a better selection of unknowns.
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