Chem exam 2

Question 1

Adsorption Chromatography

Answer 1

Uses a solid stationary phase and a liquid or gaseous mobile phase. Solute is adsorbed on the surface of solid particles. Stronger adsorption=slower movement through column.

Question 2

Partition Chromatography

Answer 2

Uses a liquid stationary phase bonded to a solid surface, typically inside of the silica chromatography column in gas chromatography. Solute equilibrates between stationary liquid and mobile phase as it passes through column

Question 3

Ion-exchange Chromatography

Answer 3

Anions such as _SO3- or cations such as _N(CH3)3+ are covalently attached to the stationary solid phase, usually a resin. Solute ions of the opposite charge are attracted to stationary phase; mobile phase is a liquid

Question 4

Molecular exclusion chromatography

Answer 4

size exclusion; gel filtration; gel permeation. separates molecules by size. larger molecules pass through more quickly. uses gel stationary phase and liquid or gas mobile phase.

Question 5

Affinity chromatography

Answer 5

most selective type of chromatography; employs specific interactions between one kind of solute molecule and a second molecule that is covalently attached (immobilized) to the stationary phase.

Question 6

Adjusted retention time

Answer 6

retention time minus time for unretained solute (mobile phase)

Question 7

relative retention

Answer 7

alpha= adjusted retention time 2 divided by adjusted retention time 1

Question 8

unadjusted relative retention

Answer 8

gamma= adjusted retention time 2 divided by adjusted retention time 1

Question 9

Retention factor

Answer 9

k= (retention time minus time for mobile phase) divided by time for mobile phase

Question 10

The longer a component is retained by a column, the ______________ the retention factor

Answer 10

greater

Question 11

scaling equation

Answer 11

(large mass/small mass) = (large column radius/small column radius)^2

Question 12

The wider the peaks the _____ their resolution.

Answer 12

poorer

Question 13

Solute moving through a chromatography column tends to spread into a ______ shape. The longer a solute remains in the column, the _____the band becomes.

Answer 13

Gaussian; broader

Question 14

Resolution

Answer 14

(change in retention time)/(average width) or (change in retention volume)/(average width) or (0.589(change in retention time))/(average half width)

Question 15

One main cause of band spreading is ________

Answer 15

`diffusion

Question 16

Diffusion is _________.

Answer 16

the transport of a solute from a region of high concentration to a region of low concentration caused by the random movement of molecules.

Question 17

____ measures the rate at which molecules move randomly from a region of high concentration to low concentration.

Answer 17

Diffusion coefficient

Question 18

Definition of a diffusion coefficient

Answer 18

Flux(mol/m2 times s) = J= -D(dc/dx)

Question 19

Diffusion in _____ is 10^4 times slower than diffusion in ______.

Answer 19

liquids;gases

Question 20

standard deviation of band

Answer 20

squareroot(2Dt)

Question 21

The _____ the plate height the narrower the bandwidth

Answer 21

smaller

Question 22

Plate Height

Answer 22

H; (standard deviation)^2 divided by distance, x

Question 23

Plate Height

Answer 23

approximately the length of column required for one equilibration of solute between mobile and stationary phases.