Exam 3 Flashcards
relative error equation
eR = x - μ / μ
chemical definition of buffer
weak conjugate acid-base pair
buffer [H3O] equation
[H3O]=Ka(CHA/CA)
buffer [OH] equation
[OH]=Kb(CA/CHA)
buffer capacity
how much acid/base you can add before a change in 1 pH unit
how to choose a buffer
with Ka as close to desired [H3O] or pKa as close to desired pH as possible
how are Ka1 and Kb2 related?
product is Kw
for H2A-, pH =
pH = pKa1 + pKa2 / 2
pH around which an indicator changes color is…
pKa of the indicator +/- 1
4 regions of acid-base titration curve, and what controls pH in each region
Initial (before any titrant is added) — acid analyte controls pH
Pre-equivalence point (buffer region) — remaining acid after reaction with base titrant controls pH
Equivalence point — pH is neutral (strong acid + strong base) or controlled by equilibrium (weak acid + strong base)
Post-equivalence point — pH is controlled by base titrant
what is special about finding pH at the pre-equivalence point in a weak acid-base titration?
it is a buffer, so you can use the buffer equation
what is special about the halfway point?
pH = pKa
[HA] = [NaX]
halfway point
what type of reaction is involved in a complexometric titration
Lewis acid-base
coordinate covalent bond
both e- come from one of the atoms
metal ions act as lewis _____, and ligand acts as lewis ______
metal – acid
ligand – base
how are ligands classified?
by number of donor atoms
ligands with one donor atom
monodentate
EDTA is a ______dentate ligand
hexadentate
EDTA full name
ethylenediaminetetraacetate
EDTA is an ___________ acid; ______ protic
aminocarboxylic
tetraprotic
how is EDTA bought?
Na2H2Y · 2 H2O
auxillary agent
lewis base added to keep the metal in solution at higher pH (prevents precipitation with OH)
displaced by EDTA
masking agent
preferentially reacts with a non-analyte metal, allowing more specificity in complexometric titration
indicators used for complexometric titrations
organic dyes
ex) calmagite; EBT
visible light spectrum
380-780 nm
definition of variables in equation for energy of a photon
E = energy
h = Planck constant
v = frequency
c = 2.998 x 10^8 m/s
ƛ(J) = c
3 fundamental properties of light waves
speed (c)
frequency (v)
wavelength (ƛ)
speed of light
2.998 x 10^8 m/s
relationship between 3 fundamental properties of light waves
c = ƛv
transmittance =
P / P0
Absorbance =
-log (T)
best range of absorbances to work with
1-2 A
(10% to 1% T)
single standard equation
Aunk/Astd = Cunk / Cstd
absorbance of a mixture is…
additive
A (total) =
A (total) = ε1bc1 + ε2bc2
isosbestic point
wavelength at which absorbance of 2 chromophores cross each other
what is special about the isosbestic point?
both species have the same ε
explain some limitations of Beer’s law
- not great at high conc.
- assume all species absorb independently
- assume all rays pass through, no scattering
- assume homogeneous mixture
- assume light applied is not enough to saturate absorbing material
- analyte may be in chemical equilibrium
refractive index (n)
n = c/v
c = speed of light in a vacuum
v = speed of light in a material
how do we take spectroscopy of an analyte in chemical equilibrium?
use a buffer (for an acid-base equilibrium)
measure at the isosbestic point
chromophore
part of a molecule that absorbs light
two types of light emission
fluorescence
phosphorescence
explain what phosphorescence is
different e- spin; longer lifetime; rare
used to measure UV spectrum
deuterium lamp + tungsten lamp
selects wavelength of light in instrument
monochromater
2 types of detectors
photomultiplier tube
photodiode array
