Analytical Chemistry 1 (correct answers)

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