SCDbase is a database of experimental
stability constants for the formation of coordination compounds (also called
complexes). The programme has a facility of graphical representations of the
relevant equilibria. The aim of this exercise is to introduce the very
existence of this data base and some of its facilities.
1. Write (on a piece
of paper) equations for the equilibrium reaction between the metal ions (with the symbol M2+)
and the ligand (with the symbol gly-)
Search in the database for stability constants for the above equilibria,
will result in a list of many experiments in which the constants are determined
with different experimental conditions. In order to work with a not too large
number of stability constants (and the relevant experiments), the search is
limited by concentrating on the experiments conducted at 25°C (exactly), where
the medium is either NaCl or LiCl
and the ionic strength is 0.15 M.
2. Search for
stability constants for complexes between the metal ion Co2+ and glycinate and analogously for Ni2+ and glycinate (for which the above experimental conditions are
fulfilled). (Notice that the ligand should be entered as the neutral compound -
here glycine or C2H5NO2 - or 2-aminoethanoic acid)
3. Store information
and the references for the experiments (you may use the notepad facility).
4.
Enter the data in the table below.
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|
log K1 |
log K2 |
log K3 |
log b1 |
log b2 |
log b3 |
|
Ni2+ |
|
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Co2+ |
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5. Read log K1
for the Ni2+ complex at ionic strength 0.1 M and at the extrapolated
ionic strength 0 M.
Now the graphical representation facilities are used. In the first
place, the distribution as a function of pH is drawn. – Remember in Main
Window to adjust the printer to the landscape format.
6. For the two experiments
chosen, click on ”Speciation”.
Under ”Reactants” the concentration of the metal ions
are set to 1 mM and the ligand concentration to 100 mM.
Under ”Constants” enter the missing constants, i.e.
for cobalt b3, and for nickel it is log b3 and the two
acidity constants if the ligand (use those given in the cobalt case)
Now, chose ”Calculate as a function of: pH”, then enter the pH interval 2-12.
Click on ”Calculate”, and finally on ”Graph”.
The text on the graphs may be edited. Use "edit titles" e.g. with the
button with the small letters).
You may add scale lines to the graphs.
Now print the graphs and answer the questions under 7 and 10 using these graphs
only.
7. For each metal ion
consider: How is the distribution of the different species at pH 7.0?
Secondly, the distribution as a function of the ligand concentration is
drawn (as pX= -log [X])
8. The window with the graph
is closed (click ”Cancel”).
Now chose ”Calculate as a function of: pX”. Set pH to 7.0, and enter the pX interval
0-10. Click ”Calculate”, and then ”Graph”.
Print the graphs (you may add some text on the graph as before) and answer the questions under 9 and 10 using only these
graphs.
9.
For each metal ion consider: How is the distribution
of the different species at pX=3.0? To what ligand concentration does pX=3.0 correspond?
10.
Using the graphs only you are able to determine which
metal ion - Co2+ or Ni2+ - forms the strongest complexes
with glycinate. What is the result?
1. Write (on a piece
of paper) equations for the equilibrium reaction between the metal ions ((with
the symbol M2+) and the ligand (with the symbol ox2-)
The search in the database for stability constants for these equilibria
should be limited by the temperature being exactly 25°C, the medium NaClO4
and the ionic strength 1.0 M.
2. Search for
stability constants for complexes between the metal ion Co2+ and oxalate
and analogously for Ni2+ and oxalate (for which the above
experimental conditions are fulfilled). (Notice that the ligand should be
entered as the neutral compound – i.e. oxalic acid)
3. Chose two
experiments as basis for the following. Store information and the references
for the experiments
4. Enter the data in
the table below.
|
|
log K1 |
log K2 |
log b1 |
log b2 |
|
Ni2+ |
|
|
|
|
|
Co2+ |
|
|
|
|
5.
For the two experiments chosen, click on ”Speciation”.
Under ”Reactants” the concentration of the metal ions
are set to 1 mM and the ligand concentration to 100 mM.
Under ”Constants” enter the missing constants.
6. Distribution of the species as a
function of pH: Now, chose ”Calculate as a function of: pH”, then enter the pH
interval 0-6. Click on ”Calculate”, and finally on
”Graph”.
The text on the graphs may be edited. Use "edit titles" e.g. with the
button with the small letters).
You may add scale lines to the graphs.
Now print the graphs and answer the questions under 7 and 10 using these graphs
only.
7. For each metal ion
consider: How is the distribution of the different complexes at pH 2.0?
8. Distribution as a
function of the ligand concentration: Now chose ”Calculate as a function of: pX”. Set pH to 3.0, and enter the pX interval
0-10. Click ”Calculate”, and then ”Graph”.
Print the graphs (you may add some text on the graph as before) and answer the
questions under 9 and 10 using only these graphs.
9.
For each metal ion consider: How is the distribution
of the different species at pX=3.0?
10. Using the graphs
only you are able to determine which metal ion - Co2+ or Ni2+
- forms the strongest complexes with oxalate. What is the result?
1. Write (on a piece
of paper) equations for the equilibrium reaction between the metal ions ((with
the symbol M2+) and the ligand (with the symbol en)
The search in the database for stability constants for these equilibria
should be limited by the temperature being exactly 25°C, the medium being
KCl and the ionic strength 1.0 M.
2. Search for
stability constants for complexes between the metal ion Co2+ and ethanediamine and analogously for Ni2+ and ethanediamine (for which the above experimental conditions
are fulfilled).
3. Chose two
experiments as basis for the following. Store information and the references
for the experiments
4. Enter the data in
the table below.
|
|
log K1 |
log K2 |
log K3 |
log b1 |
log b2 |
log b3 |
|
Ni2+ |
|
|
|
|
|
|
|
Co2+ |
|
|
|
|
|
|
5. Read the log K1
for the Ni2+ complex at 5°C and at 50°C.
6.
For the two experiments chosen, click on ”Speciation”.
Under ”Reactants” the concentration of the metal ions
are set to 1 mM and the ligand concentration to 100 mM.
Under ”Constants” enter the missing constants.
7. Distribution of the complexes as a
function of pH: Now, chose ”Calculate as a function of: pH”, then enter the pH
interval 2-10. Click on ”Calculate”, and finally on
”Graph”.
The text on the graphs may be edited. Use "edit titles" e.g. with the
button with the small letters).
You may add scale lines to the graphs.
Now print the graphs and answer the questions under 7 and 10 using only these
graphs.
8. For each metal ion
consider: How is the distribution of the different complexes at pH 6.0?
9. Distribution as a
function of the ligand concentration: Now chose
”Calculate as a function of: pX”. Set pH to 7.0,
and enter the pX interval 2-12. Click ”Calculate”,
and then ”Graph”.
Print the graphs (you may add some text on the graph as before) and answer the
questions under 10 and 11 using only these graphs
10.
For each metal ion consider: How is the distribution
of the different species at pX=5.0? To what ligand
concentration does pX=5.0 correspond?
11. Using the graphs
only you are able to determine which metal ion - Co2+ or Ni2+
- forms the strongest complexes with ethanediamine.
What is the result?
On the basis of the graphs for the three cases put in order the three
ligands, glycinate, oxalate and ethanediamine
according to their increasing binding properties relative to Co2+ and
Ni2+.
E Report:
Include relevant
reaction schemes, the data in tables with its experimental details and
references. Also include the conclusions regarding the relative stability of complex
formation with the three ligands in each of the two metal ion cases.
Finally make a detailed comparison between the strength of interaction
between the two metals and each of the the three ligands.
Please remember: the report is your
opportunity to file your experience with this database and what can be learned
by using such data.