Data input dialogue
Clicking Select on the iconbar icon, or choosing Enter data... from the iconbar icon menu will open the pH data input dialogue.
The data input dialogue is shown below.
The following data must be entered in the writable fields.
- The molecular name. This is used only to annotate the graph
- Set whether the acid is mono-, di-, or tri-protic by clicking on one of the radio icons. This action will fade and unfade the pK2 and pK3 icons as appropriate.
- The pK writable icons are used to enter the acid dissociation
constants for the acid. The dissociation constant values are entered
as the pKa values. Remember that this is
given by
pKa = - log10(Ka)
Thus, if a dissociation constant is 2.5 × 10-5, the pKa is 4.60.
- The acid volume
- The strength or molarity of the acid
- The base molarity
- The initial volume of the base (it is not necessary to start at zero if you wish to expand a portion of the resulting curve)
- The end volume of the base
Preset examples
To the right of the acid name field is a popup
menu button. The menu provided has three options, viz. mono-, di-,
and triprotic, which lead to submenus, each containing a list of
typical acids. Selecting one of these will enter the acids pK values,
and a complete set of data to allow a graph of the full titration to
be plotted immediately. The preset examples are currently 'hardwired'
into the application, but should cover a wide variety of typical
acids. The list of triprotic acids contains an entry 'Hypothetical'.
The pK values for this have been set sufficiently far apart so that
the three 'end points' are clear.
At the bottom of the dialogue are three action buttons.
Close
Pressing Close will close the dialogue. If a graph is already showing this will also be closed. Any data in the writable fields will be retained for when/if the dialogue is reopened.
Clear
Pressing Clear will simply remove any data that has been entered in to the writable fields, leaving a blank dialogue. If a graph is already showing this will be closed.
Graph
Pressing Plot will open a new window showing the details entered in the dialogue as a graph of pH plotted against the volume of base added. An example graph is shown in the next section.