Quiz 3 - Chromatography

Question 1

chromatography

Answer 1

a class of techniques used to separate components of a mixture based on physical property difference

Question 2

3 types of chromatography

Answer 2

1) thin-layer chromatography (TLC)
2) column chromatography
3) gas chromatography

Question 3

How are components of mixture separated?

Answer 3

• based on partitioning of molecules between 2 phases (stationary and mobile phase)
• polarity
• size
• volatility

Question 4

stationary phase

Answer 4

• solid phase in TLC/column chromatogrphy
• liquid phase in gas chromatography
• often composed of silica (SiOx)

Question 5

stationary phase types

Answer 5

• polar ==> referred to normal phase chromatography
• nonpolar ==> referred to as reverse phase chromatography

Question 6

reverse phase chromatography

Answer 6

• modified silica
• hydroxyl groups can be functionalized with different nonpolar groups (carbon chains)

Question 7

partition coefficient (Kp)

Answer 7

• defines the degrees of separation of the analytes (components of a mixture)
• Kp = (stationary phase)/(mobile phase)

Question 7

mobile phase

Answer 7

• solvent phase for TLC and CC
• gas phase for GC
• pure solvent or mixture of solvents
• mobile phase moves through the stationary phase

Question 8

Large Kp

Answer 8

• higher retention time
• x moves slower through stationary phase
• more polar molecule

Question 9

Small Kp

Answer 9

• lower retention time
• x moves faster through stationary phase
• less polar molecule

Question 10

TLC (thin layer chromatography)

Answer 10

• qualitative analysis
• requires a very small amount of material

Question 11

TLC uses

Answer 11

• assess sample purity
• assess polarity
• establish compound identity
• monitor reaction progress
• monitor CC seperations

Question 12

mobile phase moves through the stationary phase via…

Answer 12

capillary action

Question 13

TLC set up

Answer 13

• mobile phase solvent
• filter paper to saturate atmosphere with solvent
• lid
• TLC plate
• draw baseline with pencil

Question 14

different solvents result in different degrees of separation

Answer 14

• the more polar solvent allows for disruptions that create more separation than less polar solvents

Question 15

retention factor (Rf)

Answer 15

• used to determine affinity of a compound for stationary phase
• [spot distance / solvent distance]
• high Rf = less polar
• low Rf = more polar

Question 16

identifying compound with Rf

Answer 16

• different Rfs in the same solvent = different molecules

Question 17

assessing sample purity

Answer 17

• multiple spots = impure
• one spot = pure

Question 18

monitoring components of a reaction

Answer 18

• do different time intervals of a reaction sample to see spots appear/disappear to show products forming and reactants being used up

Question 19

reading TLC plate

Answer 19

• UV light
• staining with potassium permanganate (oxidizing product)

Question 20

unequal ratios of reactants may cause

Answer 20

multiple spots when some reactants did not get completely used up during the reaction