Acids and Bases
Calculations for a Titration Plot
Some basics from General Chem
HCl ! H+ + ClHOAc ! H+ + OAcH2O ! "+ + #"$
Kw = [H+][OH-]
Ka and Kw are the
molar equilibrium
constants
Ionization of Water
[H+][OH-] = 1.0 x 10-14
= Kwat 25 C
In pure water
Calibration
Many Things Are Not Absolute
Calibration Graph
line through center
of distribution
dN/N - normal
distribution eqn.
fraction of universe
between
x and (x + dx ) is the
probability that x will
lie between
x and (x + dx )
Method of Least Squar
Complexometric titrations
many metals form complex with a ligand:
Cu+ + NH3 ! Cu(NH3)+
Cu(NH3)2+ + NH3 ! Cu (NH3)22+
Cu (NH3)22+ + NH3 ! Cu (NH3)32+
Cu (NH3)32+ + NH3 ! Cu (NH3)42+
Kf1
Kf2
Kf3
Kf4
Zn (NH3) complexes vs lg NH3
"
theoretically could titrat
E le c t r o c h e m is t r y
Nernst Equation
Ion selective electrodes
R e d o x r e a c t io n s
oxidation - loss of electrons
Mn+ ! Mn+1 + eM is oxidized - reducing agent
reduction - gain of electrons
Nn+ + e- ! Nn-1
N is reduced - oxidizing agent
H a l
Robert G. Michel
Acid-base Titrations
Fractional Composition diagrams
Fractional Composition Equations
Let C be the (formal) concentration of a weak
acid, then the mass balance:
C = [HA] + [A-]. or [A-] = C - [HA]
Substitute into Ka
[ H + ](C " [ HA])
Experimental Error
Uncertainty
Propagation of Error
absolute uncertainty
e.g. uncertainty in reading burette 0.02 mL
relative uncertainty:
absolute uncertainty/measured qty
usually expressed as % - (0.02/32 mL = 0.06%)
std dev (s) - 0.19 !g/mL 0.02
Control Charts
Confidence Interval
Students t test
How do we verify accuracy?
Quality Control Charts
is known or
assumed
! is known
3! action line:
1 in 500
2.5 s action
1 in 100 (99%)
2! warning:
1 in 20 (95%)
Confidence Interval
The standard deviat
Analytical Chemistry
Chem 3332
Accuracy and Precision
Accuracy - is the number correct?
standard reference materials
primary standards
round robin analyses
Precision - with what confidence is the
number known?
number of replicates
standard deviati