THE CHEMISTRY OF FIVE ANIONS
Purpose?
1) Explore different types of reactions via observations.
2) Devise experimental method to identify
two unknown anions in a mixture.
FIRST WEEK
LAB
Test of reactivity via observations of all possible combinations.
FIRST WEEK
HOMEWORK
In groups of 3-4 devise experimental method to
identify a solution with 2 unknowns
Work on net ionic equations for reactions observed (pre-lab).
SECOND WEEK
LAB
Turn in experimental method (each student)
- can be typed or yellow sheet
- have a copy for yourself to follow
Group discussion of methods
Make revisions
Carry out “revised” methods to identify ions
Group discussion of net ionic reactions
1
1) Classes of Reactions
Precipitation
Acid/Base
Oxidation/Reduction (redox)
Complexation
Anions
&
carbonate
oxalate
nitrite
bromide
hydrogen sulfate
Reagents
acid/base, possible redox
nitric acid
cobalt (II) nitrate complexation, ppt.
ppt.
barium nitrate
sodium hydroxide
acid/base
hydrogen peroxide/H+ redox
(bisulfate)
2
Today: Observations of Reactivity
Anions are in 1- mL dispensers.
Reagents are in bottles. (Do not waste.)
Add the reagent drop-wise
Observe after first few drops
Observe after excess (mixed well)
If no reaction observed – 2nd test – measure T
2 mL REAGENT, 1 mL ANION, measure T before and after
Demonstration
Common errors: contaminated equipment
faulty recording of observations
not recording both drops & excess results
illegible notebook
3
Next Week…
Method Development in Groups before next class:
Develop procedure to identify two anions in mixture
Flow Chart often works well
Reagent added – Possible Observation – Interpretation, Conclusion, Next step
Usually 3-4 tests required to unambiguously identify anions
Be careful of possible interference from other anion
Record method in notebook (list group members)
Turn in yellow sheet/copy at beginning of 2nd week along with pre-lab
Presentation of method/critique by class
Individually carry out revised experimental method
Group works on Net Ionic Equations
Lab due beginning of lab period of following lab experiment
4
M
O
N
O
D
E
N
T
A
T
E
L
I
G
A
N
D
S
5
Types of ligands
BIDENTATE LIGANDS. Form two bonds to the central atom.
6
EXTRA INFORMATION FOR 5 ANIONS EXPERIMENT
Precipitation
Definition/
Experimental
Observables
Additional
Information
formation of solids
(solubility rules on page
147-149 in Oxtoby, values
of solubility product
constants in Table 9-1, p.
405 in Oxtoby)
meaning of solubility
product constants to be
discussed later)
Acid/Base
Redox
Complexation
pH change
temperature change
rxn of known acid/base
pairs
involves transfer of
electrons
involves changes in
oxidation states
reactions with O2, H2, or
other known oxidizers or
reducers
complexes often
colored
reaction of a transition
metal with a ligand
lists of common
acids/bases and their pK's
in Table 8-2, p.355 in
Oxtoby)
meaning of pKa's to be
discussed later
lists of common strong
oxidants and reductants
on website, standard
reduction potentials in
Appendix E in Oxtoby
-- meaning of standard
reduction potentials to be
discussed later
discussion pp. 131-132,
Oxtoby, examples of
ligands given in Table
19-1, p. 811 and
bidentate ligands in Fig.
19-2, p. 812 in Oxtoby
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