Analytical Chemistry 1 (correct answers)
Why separate compounds? correct answers 1- to isolate or concentrate components
from a mixture
2- to separate a component from other species that would interfere in the analysis
methods of separation correct answers extraction; crystallization; distillation;
chromatography
extraction correct answers method of separation; transfer of a solute from one phase to
another; uses two immiscible liquids
partition coefficient (extraction) correct answers k=[s2]/[s1]; used in solvent extraction
q (extraction) correct answers = V1/(KV2+V1)(^n); fraction of moles in S1
chromatography correct answers method of separation; based on different distrubtion
coefficients between two phases; one phase is stationary and the other is mobile
mobile phase (chromatography) correct answers gas or liquid
stationary phase (chromatography) correct answers liquid or solid
adsorption chromatography correct answers based on solute adsorption on surface of
stationary phase
partition chromatography correct answers based on solute dissolving into stationary
liquid
ion-exchange chromatography correct answers separation based on charge
size exclusion chromatography correct answers separation based on molecular size
adjusted retention time correct answers T(retention)-T(mobile phase)
Relative Retention correct answers T'(r2)/T'(r1); higher ratio means more separation
partition coefficient (chromatography) correct answers K= (Cs)/(Cm)
capacity factor (chromatography) correct answers k'; measure of retention; =K(Vs)/(Vm)
=Ms/Mm =Ts/Tm =(Tr-Tm)/Tm
q (chromatography) correct answers =(molesm)/(moless+molesm) =1/(1+k'); fraction of
solute in mobile phase
rate of travel of solute through column correct answers =V(velocity)*q(mobile)
, retention time (Tr) correct answers time it takes solute to go from beginning to end of
column; =L/(rate of solute travel) =Tm(1+(KVs/Vm)) =Tm(1+k')
retention volume (Vr) correct answers =Vm(1+(KVs/Vm)) =Vm+KVs
factors affecting separation correct answers difference in retention time
peak widths
gaussian peak correct answers W1/2= 2.35(standard deviation) W=4(standard
deviation)
resolution (retention) of two solutes correct answers higher R=better separation; R>1 is
good
plate theory (chromatography) correct answers separation occurs in discrete stages;
more stages=more plates=better separation
theoretical plates (N) correct answers indicates how good a column is for separation;
increasing retention time increases N
N versus resolution correct answers R is proportional to sqrt(N); N is required to obtain
a certain resolution
Plate Height correct answers height equivalent of a theoretical plate- HETP
constant of proportionality between the band width and the distance it has traveled
Van Deemter Equation correct answers H = A + B/u + Cu
u = linear velocity
A = eddy diffusion
B = molecular diffusion
C = mass transfer
-explains band broadening
Eddy Diffusion correct answers A- constant term
-depends on solute paths, size of particles; in packed stationary phase; increases with
porosity
Longitudinal Diffusion correct answers B- varies
-band broadening caused by diffusion of solute from center of band to edge of band
(higher to lower concentration)
-increasing velocity decreases effect
Resistance to Mass Transfer correct answers C- varies
-band broadening caused by time taken for solute to equilibrate between stationary and
mobile phase
Why separate compounds? correct answers 1- to isolate or concentrate components
from a mixture
2- to separate a component from other species that would interfere in the analysis
methods of separation correct answers extraction; crystallization; distillation;
chromatography
extraction correct answers method of separation; transfer of a solute from one phase to
another; uses two immiscible liquids
partition coefficient (extraction) correct answers k=[s2]/[s1]; used in solvent extraction
q (extraction) correct answers = V1/(KV2+V1)(^n); fraction of moles in S1
chromatography correct answers method of separation; based on different distrubtion
coefficients between two phases; one phase is stationary and the other is mobile
mobile phase (chromatography) correct answers gas or liquid
stationary phase (chromatography) correct answers liquid or solid
adsorption chromatography correct answers based on solute adsorption on surface of
stationary phase
partition chromatography correct answers based on solute dissolving into stationary
liquid
ion-exchange chromatography correct answers separation based on charge
size exclusion chromatography correct answers separation based on molecular size
adjusted retention time correct answers T(retention)-T(mobile phase)
Relative Retention correct answers T'(r2)/T'(r1); higher ratio means more separation
partition coefficient (chromatography) correct answers K= (Cs)/(Cm)
capacity factor (chromatography) correct answers k'; measure of retention; =K(Vs)/(Vm)
=Ms/Mm =Ts/Tm =(Tr-Tm)/Tm
q (chromatography) correct answers =(molesm)/(moless+molesm) =1/(1+k'); fraction of
solute in mobile phase
rate of travel of solute through column correct answers =V(velocity)*q(mobile)
, retention time (Tr) correct answers time it takes solute to go from beginning to end of
column; =L/(rate of solute travel) =Tm(1+(KVs/Vm)) =Tm(1+k')
retention volume (Vr) correct answers =Vm(1+(KVs/Vm)) =Vm+KVs
factors affecting separation correct answers difference in retention time
peak widths
gaussian peak correct answers W1/2= 2.35(standard deviation) W=4(standard
deviation)
resolution (retention) of two solutes correct answers higher R=better separation; R>1 is
good
plate theory (chromatography) correct answers separation occurs in discrete stages;
more stages=more plates=better separation
theoretical plates (N) correct answers indicates how good a column is for separation;
increasing retention time increases N
N versus resolution correct answers R is proportional to sqrt(N); N is required to obtain
a certain resolution
Plate Height correct answers height equivalent of a theoretical plate- HETP
constant of proportionality between the band width and the distance it has traveled
Van Deemter Equation correct answers H = A + B/u + Cu
u = linear velocity
A = eddy diffusion
B = molecular diffusion
C = mass transfer
-explains band broadening
Eddy Diffusion correct answers A- constant term
-depends on solute paths, size of particles; in packed stationary phase; increases with
porosity
Longitudinal Diffusion correct answers B- varies
-band broadening caused by diffusion of solute from center of band to edge of band
(higher to lower concentration)
-increasing velocity decreases effect
Resistance to Mass Transfer correct answers C- varies
-band broadening caused by time taken for solute to equilibrate between stationary and
mobile phase
