Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Chem Bio > Chem Sep midterm > Flashcards

Chem Sep midterm Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Biology 101 flashcards Organic Chemistry 101 flashcards
1
Q

2 MAJOR FORCES OF SEPERATION

A

Sepeartive and dispersive transport

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Essential feature of transport

A

redistribution of components in space

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Rules/limit of seperation

A

1) No absolute separations
a. Separation limitations and Detection limits
Limits in separation include
a. Physical (eg controlling t or p)
b. Chem limits (equilibrium)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

2 major forms of entropy

A

Mixing and dilution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Seperative transport of a component into different regions

A

Delta(H) - T Delta(S) - see quiz

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is chemical potential and what does it depend on

A

Gibbs free energy change upon entering a system - depends on intrinsic affinity to the phase (enthalpy) and solution (diffusion/concentration termenetropy? (RTLn(C))

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Stronger affinity menas what for enthalpy

A

Lower

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What are the laws of thermodynamics

A

0) Heat is transferable - transitive
1) Energy can’t be created or destroyed - just transferred
2nd law : Entropy – total entropy of an isolated sys can never decrease over time – is constant if process is reversible

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What is U - to

A

Q-w (heat transferred in vs work done

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

standard entropy vs entropy

A

standard entropy is a trait of the molecule while entropy of a reaction is something we calculate

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Equation for change in entropy

A

Change in Q/T

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

For LLE -practice solving for Q

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Uint vs u ext

A

mathematically equal (need to become 0) but different in unit abrupt whereas uext continuous

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the distribution isotherm

A

Graph of concentration in one solvent vs concentration in another (so slope is K) - at one temperature - shows that for most concentrations - this is a lienar and predictable relationship (except when concentration too high

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what is k

A

moles in stationary/moles in mp

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Binomial distribution know it

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What does craig appartus tell us about chroamtography

A

Tells us how it’s distributed - can’t give us shape and position however

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Why is the Craig Apparatus and chroamtography able to separate compounds (what equations and relations make this so)

A

So if we think of our craig apparatus dist as gaussian peak - our mean is RP, and our stdev is ROOT(rpq) so we see our mean increases proportionally with R while our spread increases only with root R so our distance is increasing faster than the spread of our peaks

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are p and q in terms of k

A

p is k’/(1+k’) and q is 1/(1+k’) and k is just q/p

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is dead time a function of

A

column dimensions and mobile phase velocity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is Rt based off of

A

column, mobile phase type and velocity, temperature and characteristic of the analyte

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Dilution equation?

A

Delta(S) = nRln((Vfinal)/(Vinitial))

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How do you get Vm and Vr in basic chromatography

A

= Ft so Ftm gets Vm, F*Tr gets Vr and can get adjusted retention volume as Vr - Vm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

k = (in terms of RT)

A

adjusted RT/ TM

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

All the things k =’s

A

q/p, tr’/tm

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

How to derive k = tr’/tm from k = q/p

A

Determine velocity i(average) in terms of average velocity of the mobile phase and p and q and solve for p and q. Convert those velocities into tr and tm through distance L. DO OUT ON PAPER

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is alpha Selectivity factor or RRT)

A

KB/Ka or kb/ka or also RTb/RTa (always greater than 1) also deltav/average(V)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is z in the gaussian dist

A

sample x minus the mean divided by stdev (so basically difference from mean, normalized or expressing it in #’s of stdevs)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

W at different heights in terms of stdev

A

Base = 4 stdev, at half its 2.35 stdeev

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

Gaussian distribution as applied to concentration profile of a peak

A

c(t) = cmax * e^-((t-tr)^2)/(2stdev^2)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

How does theoretical plates relate to how Craig apparatus is able to separate?

A

so theoretical plates = (tr/stdev)^2 and this is analogous to R (so the more we have tr goes up higher, and stdev increase proportional to root (N)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What is effective plate # and relation to N

A

RRT/stdev squared; Neff = N *(k/1+k)^2

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

Equations for H (height in theoretical plates)

A

L/N, variance/L, X/N, variance/X, X*W2/(16tr^2)

so in sum things it could be related to are L, N, X, W, Tr

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

Calculate resolution

A

(difference in Tr divided by average W)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Resolution scales

A

Adequate is 0.8, 1-1.5 is great, 1.5 is baseline(>99% separation)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

Write out how migration distance effect on Rs depends on Delta X (start with resolution equation in terms of X)

A
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

Resolution plot that comes from showing Rs proportional to ROOT(X)

A

Y axis is resolution, and X is distance of migration (X) - and we have a plot for DELTA X (the top of the Rs equation ) - being proportional to X so it’s linear, and we have a curve for the bottom (average W) which since its proportional to ROOT(X) is a curve - and where they meet is where R - 1 (makes sense) and - after that point we see that our DELTA X line is bigger than the average W curve showing that our R will be greater than one after that point with increased migration distance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

How does selectivity play into our resolution plot

A

So in the top part of resolution DELTA X - we determined equaled Delta v tr, in which we sub tr for X/V which gives us (Delta(v) /V)X in our first plot we just had X as a line and now delta v/V is OUR SLOPE FOR THE LINE and this delta v/v is our selectivity so as our selectivity is greater(alpha = tr’/tr’ or K/K or k/k) the slope is higher and we reach a resolution of one with less migration distance of X

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

How does Plate height play into our Rs plot

A

For our resolution plot equation - we instead of just saying the denominator is proportional to ROOT(T) we take it literally - we went from Average W to 4ROOT(H*X) which if we we square the inside but take a root of it we can rearrange to to 16H so smaller plate height better -

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

How does N enter the resolution equation

A

So when we have DeltaV/V *ROOT(X/16H), X/H = N so it becomes Delta v/v * (N/16)^(1/2)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

derive the purnell equation

A

Start with resolution but in terms of rt - Assume W for both are so average W = W, and replace that with sigma and replace sigma with the theoretical plate equation (in terms of N and rt) THen , replace the rt’s with tm(k+1)’s , work that out and sub in alpha = k2/k1 (IDK how the math works but it works)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

What are the purnell factors and how do they affect resolution

A

Selectivity, N and K; as k increases our peaks have more affinity for SP - move farther along - some resolution but broader peaks, as N increases, we get sharper peaks - same Rt sep but less sigma so better resolution, and Selectivity - makes a big difference eg change mobile phase now they will move differently from each other

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

How do the effects of the fundamental purnell factors change as they increase

A

Alpha is fairly linear throughout - better returns, N and K have points where their slopes become really shallow - pretty early for N and K, earlier and shallow for K though

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

are the fundamental factors *purnell) independant?

A

no

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

What is peak capacity

A

The number of peaks we can fit along a length (essentially L/W*Rs) an be turned into root(N)/ 4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

more accruate peak capacity equations

A

nc = 1 + (ROOTN)/4 * ln(Vmax/VmiN)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
47
Q

Explain alternate isotherms

A

Langmuir -so we have stronger interactions with SP and MP SO as concentration goes up - the SP gets SATURATED - and at these higher concentrations then - we see k go down - so tr goes down and vi goes up. So the center of our peak moves Faster - in DISTANCE - this creates a tailing peak but iN RT (keep in mind faster means lower RT) - this makes a shark fin tailing peak -
Anti LANGMUIR- the opposite - more affinity for MP - see the opposite happen - creates fronting peaks

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
48
Q

Write out the Vi and Tr equations for isotherms in terms of k

A

so vi = vm/(1+K) and tr = tm(1+k) so we see tr increases with k and vi goes down as k increases.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
49
Q

Tailing asymmetry equiations

A

asymmetry factor: b/a at 10% (b being behind the peak so > 1 is tailing.
ALSO tailing factor - a+b/2a (at 5% height) - 1 = even no tailing)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
50
Q

pros and cons of fluid

A

(a) The strength of flow: provides the most powerful and versatile
mechanism of transport available for separative displacement.
(b) The weakness of flow: its nonselectivity and nonuniformity.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
51
Q

Know the relationship between volume, tr and tm, Flow rate length etc

A

Start with vm = L/tm end with L*F/V (note little v is velocity) big V is volume. Can do with dead volume or just mobile phase flow and also do with SOLUTE flow rate (tr)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
52
Q

What does flow depend on in terms of viscosity

A

viscosity , area of contact between fluid layers, dv/dy (how velocity changes with y)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
53
Q

How do we calculate Reynauds factor

A

INERTIA/VISCOSITY (inertia = pvd (solvent density * velocity * pipe diameter).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
54
Q

3 types of flows and expected Reynaud factors?

A

Plug, Turbulent and Laminar
Plug - infinite -
Turbulent - > 2100 (has laminar zone on edges and turbulent area in middle)
Laminar - < 2100 - center is vmax (Hagen Poiseuille Flow

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
55
Q

What is the Hagen Poiseuille equaiton and what does it tell us

A

Vmax in terms of pressure drop (for laminar flow)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
56
Q

How do you calculate the velocity of a particle x distance from center in a laminar flow

A

vmax (1-(x^2)/(r^2)) r being radius of tube

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
57
Q

Talk about the basis for Hagen-Poiseuille and how it takes it’s final form

A

It’s essentially- Change in pressure = Flow * Resistance . It dictates average v is proportional to radius of pipe (squared), and change in pressure and inversely correlated with Length of pipe and viscosity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
58
Q

Volumes in a column and how they’re divided into porsoities

A

so theres overall voluKnowme, interparticle volume and intraparticle volume (so volume inside our particles vs outside it (stagnant vs flowing) - our porosities are then
EE- INTERPARTICLE POROSITY (volume outside of particle/empty column)
EP - INTRAPARTICLE(volume in particle/empty column)
and TOTOAL POROSITY) -EE + EP (void volume of column/ empty column)
* NOTE DIFFERENCE IN VOID VOLUME VS EMPTY COLUMN

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
59
Q

Common porosities

A

EP often .4, EE often .4 and E tot often .8

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
60
Q

How does REYNAUDS # change in packed bed and what are the relative #’s expected for flows

A

instead of d being diameter of pipe - it’s particle diameter
Turublent is > 100
1-100 is a mix of turbulent and laminr
Laminar is < 1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
61
Q

How does Hagen Poiseuille change in packed bed

A

So instead of r for radius of pipe we have B -specific permeability constant, also instead of in denominator we also have EE (so Bo is R^2/8 (AN OPEN TUBE) which is why it replaces both of those values)
THIS IS DARCYS LAW

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
62
Q

For a packed column , what does B depend on and what is an approximation for B in common column types

A

B depends on EE and particle diameter (positively with both), for a regularly packed column its roughly d^2 / 1000 for a bed packed with spherical particles d^2 /500

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
63
Q

Relations in the OVERALL DARCY equation (subbing in the karman conzeny eq for Bo)

A

Vavg is proportional to changein pressure, particle diameter ^2, inverse proportional with viscosity and length, and generally proportional to EE

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
64
Q

relationship between v avg and vm in packed bed

A

V avg is the set flow I guess and v m is the Actual flow
Vavg* (EE/Etot) = Vm and if we use ee = .4 and eep = .4 we get vavg = vm*2 (VM is less than v avg

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
65
Q

Bo in terms of vm?

A

vm *n * ETot * L divided by delta P

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
66
Q

Given Darcy equation whats the relation between change in pressure and dp

A

inversely related (dleta P = vavg * (constant/dp^2))

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
67
Q

Know how to put Vm into Darcys equation (relate Bo to Vm)

A

Start with Darcys, sub in vavg = VM *(ETOT)/(EE)) rearrange for BO

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
68
Q

Mass Transfer and Diffusion definitions

A

Mass transfer: movement of mass from one place to another
Diffusion: movement of mass from region of high concentration to low
concentration.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
69
Q

How to get the mean for a random walk

A

binomial distribution

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
70
Q

How do you get the overal mean of several random walks

A

Kl - (k-1)l

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
71
Q

How do you get variance of random walk

A

know how to do this

72
Q

How do you get drift velocity from random walk

A

n * delta t = t from this can sub in for N in terms of T and X/T = v

73
Q

How do you get einsteins equation from random walk

A

The variance equation - sub in t/Delta T for N and sub in D

74
Q

diffusion coefficient in terms of l

A

D = (l^2)/2delta(t)

75
Q

Rewrite band broadening (gaussian function) in terms of diffusion (einsteins)

A

replace all the sigma ^2 with 2dt
but otherwise same equation Ct = cmax etc

76
Q

How to get plate height theory of columen efficiency (from random walk)

A

given our diffusion being variance = 2dt, D also = l^2 /2delta(2) so if we sub that in we get l = sigma - SO we can take H = variance/L - sub in N*l for variance and then n/L = H so l^2/H = H so l = h

77
Q

How do we caluclate N for particles moving across plane in one direction

A

N(x-l/2) = 1/2( Nx - Nx-l)

78
Q

How do we derive ficks first law

A

so we need 3 equations N moving across a plane is L/2 * dN/dx, N = c(x)LYZ and J = N/(YZdelta(T)) and for the J equation first sub in L/2dN/dx for N and then sub in c(x*LYZ for dN - sub in D for l^2/2t and done

79
Q

How do we derive ficks 2nd law

A

We start with N/YZdelta t = J - turn it inot delta N and delta J and sub in N - c(x) *LYZ, and divide both sides by L this makes dN/dt = dJ/dx then sub in for J (-D dc/dx)

80
Q

what does ficsk 2n dlaw say

A

Fick’s 2nd law of diffusion describes the rate of accumulation (or depletion) of concentration within the volume as proportional to the local curvature of the concentration gradient.

81
Q

what does ficks first law say

A

Fick’s first law tells us HOW MUCH flux to expect

82
Q

For a particle in solution moving at velocity and is colliding upon - what is the equation representing its distance and its velocity

A

x = vo*t + (1/2) f/m * (t^2)
v = v + (1/2) f/m * t

83
Q

What is stokes law

A

friction coefficeint = 6 pi r n(viscosity)

84
Q

Derive friction equations and use those with diffusion to get einstens famous equation (and expand with components that make up friction)

A

so from velocity equation the f term is 1/2 * f/m t and friction is kind of inverse 2m/t - friction also equals 6 pi r viscosity. D = l^2/2t so when you do D * friction you get mL^2/t^2 and l^2/t^2 = v^2 so we get mv^2 so we can say Dfric = Kb *T, we can divide both sides by friction and sub in 6 pi r viscosity (which is STOKES EINSTEIN

85
Q

What is mobility (u)

A

1/fric

86
Q

What is c (or dc)

A

density or change in density

87
Q

How are boltzmanns and R and avogadros related

A

R = kb * T * Na

88
Q

What does diffusion depend on in a system

A

solute solvent and temp

89
Q

Typical diffusion constant valules

A

around 1 in gases and around 10^-5 to 10^-7 in liquid

90
Q

Issues with diffusion in a packed bed

A

Tortuosity and bottleneck problems, tortuosity is that there are many winding paths and bottleneck is some of these paths are narrower - decrease rate of diffusion

91
Q

friction coefficient

A

Na * friction coefficent (MOLAR DRAG CONSTNAT

92
Q

Know how to derive molecular transport equation

A
93
Q

what is transient

A

M/f (1/A0 time it takes for acceleration

94
Q

does the transient matter

A

typically very small reduces the whole term essentially to 0 - that’s us reaching steady state velocity - acceleration died down really quick because too much friciton/collisions etc

95
Q

Derive the Flux of molecular transport

A
96
Q

What do the terms in flux of molecular transport mean

A

U is mean displacement from external and internal forces and D dc/dx is our dilution entropy term

97
Q

What is diffusion interms of molar drag coefficeint

A

D = RT/f ( this works because D(fric) = Kbt and f = (fric)Na so substituting it gives Na*Kb on top which gives R

98
Q

For our overall Flux molecular transport equation - how does that relate to Ficks first law

A

It’s ficks first law with UC so if there are no external or internal forces - becomes ficks first law (no U force)

99
Q

How do we relate our overall flux transport o Ficks 2nd law

A

see notes

100
Q

What is w

A

w replaces Uc - representssimply the sum of all direct (non-diffusional) displacement
velocities– those caused by bulk displacement at velocity v plus those
caused by chemical potential gradients which impel solute at velocity U

101
Q

Transport equation on a gasussian curve

A

so at one point in a peak we see dc with respect to dt is going up and we see that s proportional to -W dc/dx = so going from high concentration to low? as we go along its less BUT ITS negative - so the stuff moving out is less and more is coming in

102
Q

3 PROCESSES that affect band broadening

A

(1) Longitudinal diffusion
(2) Eddy multi path diffusion
(3) Partition between stationary phase and mobile phase

103
Q

To understand band broadening in a column using random walk - whats our first step

A

Determine step length and Number of steps

104
Q

Whats longitudinal diffusion in an open tube vs a packed bed and how is it derived

A

Open tube: 2 dm/v (comes from einstein equation variance = 2dt = 2dmL/v and variance/L = Hl

FprPacked bed - it’s the same equation but we multiple velocity by (1 + ep/ee)
eventually turned into Hl - 2yDm/v (with y being that term we added)

105
Q

In terms of eddy diffusion - what are ways CRITICAL VELOCITY BIASES arise

A

molecules traveling faster at center of narrow flow channels
molecules travel faster in some channels than other due to shape, openness etc
molecules travel faster in some region due to packing differences
molecules travel faster outside of pores than in them

106
Q

How to use random walk to define EDDY DIFFUSION

A

1st assume constant v in our segment which is the size of our site (so # of segments = L/S) - can change v between S’s but not within - SO to determine our step size - we compare the S of a normal velocity (average) to a fast one and the difference is our step size (so the difference would be (Vf-v)t - and we sub in for t with S/v so we get (vs-v) S/vf and we can replace all the v terms with w so its jus W^2 *S =HE

107
Q

2 ways a molecule is removed from velocity bias (eddy diffusion )

A

Flow - they’ll naturally flow to the next S which may be faster , slower or the same - DIFFUSIOn - they can diffuse between fast an slow paths randomly

108
Q

Equations for molecules removed from velocity (flow vs diffusion dominated)

A

hf = 2 lambda *dp (flow)
Hd = (wdp^2)/Dm * v (diffusion - Dm is diffusion coefficient in MP)

109
Q

In eddy diffusion how do Flow based and diffusion based interactive (derive the additive plates)

A

In terms of random walk steps - They are additive! So we can solve for S (L/N - and sub in N for N from D and N from F and from there add in the W term and simplify it

110
Q

How do the combination of Eddy diffusion factor look graphically

A

on velocity vs H - HF is independent of velocity so its a horizontal line, Hd is a line - linear BUT HE - is in fact a curve that approaches 0

111
Q

Get He equation not in terms of Hd and Hf (sub these values in

A

see notes

112
Q

What does He relate to

A

dp (correlates to) - inverse correlate with diffusion- correlate positively with v

113
Q

How does mass trasnfer effect flow -

A

largely in how it takes time- different distances from the phase IN addition to it just taking different amount of times in and out

114
Q

Equations for Hs and Hm (resistance to stationary and mobile phase)

A

see notes

115
Q

Relationship between Hr and Hs and Hm

A

additive! Hr - Hs + Hm

116
Q

Know VAN DEEMTER TERMS andH’s correpsonding to them

A
117
Q

Band broadening tips tips

A

Smaller particles for packed column
Smaller diameter for open column
Lower temperature and higher flow rate to reduce longitudinal diffusion
Most separation is operated in flow rates higher than the optimum flow rate, thus C term is significant in overall separation performance

118
Q

What is minimum for van deemter and how derived?

A

Take derivative and solve - take 2nd derivative to see if min or max (its a min)
𝑣_𝑜𝑝𝑡=(𝐵⁄𝐶)^(1/2)
𝐻_𝑜𝑝𝑡=𝐴+〖2(𝐵𝐶)〗^(1/2)

119
Q

What do the diffusion equations describe

A

The diffusion equation describes Brownian motion for
a large number of particles

120
Q

What are the names of k, k’, Dc and K

A

k is the retention factor (capacity factor), Dc is the concentration distribution coefficient, K is the distribution partition coefficient (Distributio coefficent)?

121
Q

In which system GC or LC is longitudinal diffusion more important

A

GC

122
Q

So for Eddy diffusion plate height which equation is used when and what are the terms

A

Hf is used when flow is the dominant mechanism, (Hf = 2lambda dp) and Hd is used when diffusion dominates w*dp^2 * v / Dm (solution diffusion coefficient)

123
Q

What is plate height eddy proprtional to

A

lamba (column packing factor 0.5-1.5), dp, and velocity - inverely proprtional to diffusion of mobile phase (x is also in this dp is to 1+x, v to x and dm to x - x = 0 for GC 1/3 for LC) -

124
Q

The effects of Dm and v as compared He to Hl

A

Opposite - Hl = 2dm/v He is 2 lamba dp V/dm

125
Q

What happens if slow mass trasnfer time

A

lagging peaks

126
Q

Knox eq

A

He (flow term) + Hl (packed) + Hm + Hs and can write it interms of v (so the He term which is a is v ^1/3 , the B term for longitudinal is B/v and the Mass transfer terms are x v (cm + cs)*v

127
Q

Which tings go up and down for which terms in van deemter (for v, D, dp, df (thickness off stationary) and k)

A

v - goes down Hl up for everything else (unless He is flow in which its independent)

D - up for Hl down for everything else
dpup for everything

df (up for Hs)
k - up for Hm down for Hs

128
Q

In rate theory of bandbroadening - we ca new sum up all of these lplateheights

A

necause they are all our variancces and can be summed up

129
Q

optimal velocity van deemter

A

ROOT(B/c)

130
Q

Simplified van deemter equation

A

Htot - A +B/V +Cv

131
Q

H opt

A

A + 2(BC)^1/2

132
Q

Summary of band broadening

A

Smaller particle for packed column,
smaller diameter for open column,
low temp and high flow rate to reduce longitudinal diffusion,
A lot of separation ran higher than optimal flow rate so C term is significant

133
Q

What are things in the Hs term

A

k, qs (shape factor 2.3 for thin layer on support), df - thickness of stationary, Ds - diffusion in stationary )inverse with Ds

134
Q

Things in hm term

A

k, dp, v and dm (inverse

135
Q

What is x in He and what does it depend on

A

0 for Gc, 1/3 for LC

136
Q

What is W in moleular transport with flow

A

W is the sum of uint, uext and v from flow

137
Q

physical interp of transport equation

A

so our equation is J = -W(Dc/dc) + D Dc^2/dx^2 so J or dc/dt is proprtional to -W(dc/dx) which makes sense

138
Q

What does J =

A

dc/dt, ; N/(YZdt)); Ddc/dx; UC + (1/f)Ddc/dx

139
Q

Why use a packed column isntead of a stationary columns and how does that effect the column dimensions

A

So in an open column - a solute is far from the stationary phase and interaction really depends on distance SO - for this open columns you need to make their diameters really small (also as a means of increasing relative Vs) For a packed column however, not necessarily the case - this everywhere - as such larger diameter - and has higher sample capacity then for potentially an equivalent Vs

140
Q

What are poise units

A

g/(cms) or (Newtons )/m^2 or Pas (so a Pa is Newton/m^2) (newton is kgm / s^2) WATCH OUT FOR PROBLEM S TO MAKE SURE OTHER UNITS the same - like for Reynauds everything g/cm etc BUT in stokes radius - have Kb so every thing needs to be in Nm (so you would convert other numbers to match meters)

141
Q

How to solve lengthening resolution problem

A

Rs /Rs = ROOT(N)/ROOT(N) so the first root N is the more retained - and then you KEEP THE SAME H from previous then h=l/n get new L

142
Q

What causes a langmuir isotherm -

A

Saturation of solid phase so at higher concentration an unexpected amount remains in mobile phase and goes faster

143
Q

How does anti-langmuir occur

A

Solute solute interactions strong - so as concentration increase - as more goes into stationary phase - actually creates a mixed phase that allows increased solubility of the solute so more go into the stationary phase than expected to slower than expected. Can also occur in GC if over inject (more concentration than can be possibly vaporized some stays in liquid phase in the stationary phase

144
Q

spontaneous process (G and S

A

G negative, S positive(at least balanced by H

145
Q

Limits on stokes law

A

In the limit of low Reynolds number, the mobility μ is the
inverse of the drag coefficient ζ. For spherical particles only of
radius r, Stokes’ law gives

146
Q

When we are calculating mean displacement of a collision what do we assume

A

assume v0 is 0 so all of the force is from acceleration and friction

147
Q

Why is diffusion in liquids slower

A

density and high chance of reactions between the solvents

148
Q

What is step 2 of getting the stdev of random walk

A

N(ql^2 + (1-q)l^2 - triangebrack(x)^2)

149
Q

How do we go from stdev of random walk to Plate column efficiency

A

assume q = 0.5 - then stdev simplifies into variance = Nl^2

150
Q

dG for closed system

A

0

151
Q

closed system dG equ

A

dG< PdV - SdT

152
Q

What is the K used for lle and the like (

A

K distribution coefficient

153
Q

in an overall closed system what’s true about uB and ua

A

need to equal each other (overall change in gibbs must be 0

154
Q

Delta H in a partition between two liquids

A

For general separation system involving a partition of
components between phases
Intermolecular interactions
dominate
so H should be greater than S*Delta T

155
Q

relation between N and N eff

A

Neff = N *(k/1+k)^2

156
Q

What is H useful for in chormatogrpahy

A

H is useful in comparing the efficiencies of different sized columns
or different support materials.
* It is also heavily used in chromatography theory to relate various
chromatographic parameters to the kinetic processes occurring in
the column

157
Q

H in terms of X and tr

A

H = XW^2/16tr^2

158
Q

Estimatino for peak capacity assumes what

A

Rs = 1

159
Q

how flow relates to V

A

flow = P/R

160
Q

void volume/total column volume

A

For most porous supports, εtot ~ 0.8 (i.e., in average 80% of the
column is occupied by mobile phase and 20% by the solid support

161
Q

bo for open tube

A

R^2 /8

162
Q

EP vs EE

A

EP is intra particle, EE is interparticle

163
Q

konzeny carman issues

A

really only works for irregular packing - typically produces a Bo greater than actual

164
Q

u

A

1/zeta *wierd fric)

165
Q

Molecular transport is written in what quanttity

A

molar (all of the terms are MOLAR terms - eg f is molar friction, M is one mole of substance, du dx is effective force per mole

166
Q

What is Hd and Hf

A

2 lamba dp and wdp^2*v/Dm

167
Q

what is lamba

A

column pakcing factor .5-1.5

168
Q

x what is

A

system constnat (0 for gc 1/3 for lc

169
Q

what is qc for a thin layer support

A

2/3

170
Q

Different van deemter forms for GC and LC

A

Van deemter A + B/V + C *V is GC (longitudinal form) then the LC form is knox (and the Z is Z *V^1/3 assuming max gamma

171
Q

What are the A B and C terms in van deemter

A

A is EDDY diffusion, B is longitudinal and C is mass trasnfer

172
Q

Units for diffusion

A

cm/s^2

173
Q

Units needed for solving for J *U int, uext etc

A

kg/m*s mL

174
Q

Units of reynolds flow rate

A

mL(?)/sec!

175
Q

packed gc column use gamma

A

yes for HL

176
Q

how to do transient time calc

A

so its m/f However the M can be in u or daltons and this is taken care of because f is already molar (so if have zeta need to multiply it by avogadors - if have f - stay the same)

Chem Bio (17 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions