Purity determination and compounds separation

Question 1

Solubility of acids

Answer 1

• Dissolved well in non polar organic solvents at low pH
• Soluable in polar solvents at a high pH

Question 2

Solubility of bases

Answer 2

• Solubility in organic solvents when the pH is high
• Soluable in water when the pH is low

Question 3

When is seperation required

Answer 3

• If comound isnt pure after partition purification is required

Question 4

Purification

Answer 4

When the compound is pure after partition (solid and liquid)

Question 5

Recrystalisation

Answer 5

• Solubility of solids increase with increased temperature
• Required desired product to no be soluable in room temperature but in a hot solvent
• Imurity must be soluable (or partially) at room temperature and when solvent is hot
• Add impure and desired to hot solvent allow to cool to room temp and desired will recrystalise

Question 6

Distillation

Answer 6

• Liquid converted to vapours by heating then condensation of vapours via cooling
• Seperate non volatile liquid from volatile as they have diffrent boiling points

Question 7

Chromatography

Answer 7

• Seperating mixture into components identify components and measure the concentration
• Distribute components between 2 phases
• Partition coefficient = solute phase 1/solute phase 2
• Higher partition coefficent means higher ratio of concentration
• Mobile phase gas or liquid stationary is solid or liquid

Question 8

Process of chromatography

Answer 8

• Sample containing 3 components are placed on colum containing stationary phase
• Sample is carried along the column by the mobile phase the component spreds out
• End od column the components are seperated due to diffent speed and affinity to stationary phase

Question 9

Thin layer chromatography

Qualitative

Answer 9

• Thin layer of absorbant coating (SiO2 and Al2O3)
• Small amount of sample solution spotted on the plate
• End of TLC immersed into pool of solvent
• Placed above solvent moves up stationary phase via capillary action

Question 10

Retention factor

Answer 10

Distance travelled by solvent/Distance of solvent front

Question 11

If compounds in chromatography are colourless?

Answer 11

• Add fluorescence to stationary phase which will glow when exposed to UV ligtht
• Areas containing solute will not glow and appear darker (mobile phase)

Question 12

Stationary phase

Answer 12

• Silica gel (silica oxide)
• Very polar free OH group can form hydrogen bonds vander waals forces and dipole dipole interactions

Question 13

Polar compound attraction to stationary phase

Answer 13

More polar compounds more formation of H bonds with silica gel more firmly so stronger absorbtion

Question 14

Non-polar compound attraction to stationary phase

Answer 14

• Forms weak vander waals forces so less attraction so carried more by mobile phase
• Low polarity compound has higher rf value than high polarity

Question 15

Mobile phase

Answer 15

• Ability to dissolve ‘like dissolves like’ how fast they move up the TLC
• Polar compounds run faster in polar solvent and non polar in non polar solvents

Question 16

Mobile phase absorbtion to stationary phase

Answer 16

• Ability to be asorbed by silica can displace compond and push up the TLC plate (affinity to the stationary phase)

Question 17

Solvent too strongly absorbed

Answer 17

• Fully displace all compounds they all move up the TLC plate and no seperation occours

Question 18

Solvent too weakly absorbed

Answer 18

• Solvating power is too weak to move the compound up the TLC to show enough seperation

Question 19

Eluting strength

mobile phase

Answer 19

How strong it is absorbed on the silica which increases with solvdent polarity