A balanced chemical formula gives the ratios, in
moles, of materials produced or consumed in a
2NaI(aq) + Pb(NO3)2 (aq)
PbI2(s) + 2NaNO3 (aq)
If the weight of any one species used or produced
is known, the others are readily calculated.
Both oxidation and reduction occur during a
The equivalence point is based on the
concentration of the oxidized and reduced form
of all species involved.
Aox + Bred = Ared + Box
Ce4+ + Fe2+ = Ce3+ + Fe3+
For a REDOX titration, the equivalence p
Energy of photon = h!
h - Plank’s constant
! - frequency (sec-1)
Common " units
µm - 10-6 m
nm - 10-9 m
"! = c
c - speed of light
A - 10-10 m
As " increases, the frequency and energy of the
< 10 nm
< 10 nm
UV/Vis absorption by organic compounds
requires that the energy absorbed corresponds
to a jump from a populated orbital to an
Vapor phase spectrum
The equipment used share any common features
regardless of the ! being measured.
Each will have a
Early absorption methods were
based on using the human
eye as our detector.
We’ll now look at various equipment
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I " f u Atomic SPBIOScopy
f These methods deal with the absorption
' and emission of radiation by atoms.
.' " General concerns and considerations.
Atomic spectra have narrow lines.
This is powerfu tool for the idntification of
o It relies of the production of ions from a parent
" compound and the subsequent
characterization of the patterns that are
0 While it is a qualitative tool, it can b
For a solute, Z, in equilibrium exists between an
aqueous and organic solvent:
At equilibrium, we have:
KP = [ Z ]1
This assumes ideal behavior at low
concentrations. It actually results in a ternary
When dealing with aqueous speci
Chromatography - “color” and “to write”
Originally described by Tswett - 1906
He devised a method to separate plant
pigments using a tube filled with CaCO3.
After adding a plant extract, he was able to
produce several colored bands by washing the
a - compressed gas cylinder
b - pressure regulator
c - valve
d - filter
Purpose of port is to flash evaporate your sample
and introduce it into the column.
First chromatographic method described (as a
Since samples don’t need to be initially
vaporized, potentially any compound can be
assayed by this method.
Instrumental development lagged behind that of
GC because of difficulties in
Combination results in 3-D data providing both
quantitative and qualitative information.
One critical aspect of GC-MS and LCMS is the interface.
Both chromatographic approaches
have relatively large flows.
GC - 1 - 50 ml / min
LC - 0.1 - 5 m
The cell current is
electrolysis at various
Most common electrode
type is a dropping
A current vs. potential
curve is produced.
With electrodeposition, the goal to to
convert all of our analyte from
With potentiometric methods, we simply
measured Ecell and used the Nernst equation to
quantify a substance.
With electrogravimetry and coulometry, a
potential is applied, forcing a reaction to go.
- polarize the cell
- causes unexpected things to happen.
The previous cell would be difficult to use for
We would like something that can be placed
in the solution we wish to measure.
The electrodes we’ll be looking at have that
goal in mind but still represent a complete
electrochemical cell w
For this simple procedure, we have a
minimum of five sources of error.
Each can occur as a + or - error.
Our total error becomes:
ET = + Ewt1 + Evol + Edrain + Ewt2 + Edensity
And this was for a simple example.
Identifying sources of error can help you re
By accurately measuring
the volume of titrant that
is added, the amount of
sample can be determined.
A buret is used to control
and measure the amount
of titrant that is added.
titrant - AgNO3
- a standard soluti
Many analytical methods rely on equilibrium
systems in aqueous solution.
This unit will review
General concepts of aqueous solutions
Deviations from ideal behavior
base of HF
acid of H
In the last unit we reviewed the common types
of equilibrium expressions.
The examples typically dealt with relatively
simple systems with only a single equilibrium
to work with.
It is much more common to have two or more
As with other types of reactions, the formation of
a precipitate can be used as the basis of a
analyte + titrant
The approach assumes that under the
experimental conditions used, the product is
This is a quick and accurate method for
determining acidic or basic substances in
Several inorganic acids and bases.
Hundreds of organic species.
The titrant is typically a strong acid or base.
The sample species can be either a strong or
It is still possible to develop analytical
methods for species that contain
multiple acid or base groups.
This unit will review the types of
calculations and titration curves
Some specific examples will also be
The major reason is that many acids and bases
cant be quantitatively in water at reasonable
The problem occurs when the pKA or pKB of
our material is > 7.
The endpoint is not a sharp break so is very
difficult to detect.
L - ligand
M - central species
X - counter ion
Another factor is the coordination number of the
central species - bonds formed.
2 - linear
4 - tetrahedral / square planer
6 - octahedral
Possess only one accessible donor gr
Not all reactions will proceed rapidly.
Earlier, we pointed out that as a reaction
proceeds, it will have an initial kinetic region
where concentrations change as a function of
Most quantitative methods rely on the use o
Oxidation-Reduction - REDOX
A chemical reaction where there is a
net change in the oxidation number
of one or more species.
Both an oxidation and a reduction
must occur during the reaction.
The species that loses electrons during the
Causes a re
A large portion of this course deals with methods
that are used to determine how much of a
material is present.
We need to review the general steps that are
taken for any quantitative method.
These steps are taken to insure an accurate
and reliable answer