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Titration Applet

Ratings

Overall Rating:
Content Quality:
Effectiveness:
Ease of Use:

Reviewed:	May 04, 2005 by Chemistry Editorial Board
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.
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.
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.

Evaluation and Observation

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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Peer Review

Titration Applet

Ratings

Overall Rating:

Evaluation and Observation

Content Quality

Potential Effectiveness as a Teaching Tool

Ease of Use for Both Students and Faculty