Separation and Purification

Question 1

Gas Liquid Chromatography

Answer 1

separates molecules based on boiling point

higher boiling point remains in liquid phase longer and becomes separated later than lower boiling point materials

Question 2

Factors in determine high boiling point of molecule

Answer 2

stronger intermolecular forces (harder to separate molecules)

heavier molecular weight (larger surface area and therefore stronger london forces)

branched molecules (larger surface area)

Question 3

How to improve separation for chromatography?

Answer 3

increase length of column

chromatography separates compounds based on affinity for stationary phase over mobile phase. Allowing the molecule more time to interact with the stationary phase improves resolution of each compound

Question 4

What would happen if you increased initial temperature for chromatography?

Answer 4

would cause increased flow rate which would lead to a lower resolution of compounds

Question 5

High Performance Liquid Chromatography

Answer 5

purification method that separates mixtures based on the component’s affinity for the stationary phase

Question 6

distillation

Answer 6

technique that separates liquid molecules based on boiling points

the compound with the lowest boiling point evaporates first

Question 7

simple distillation

Answer 7

best suited for compounds with boiling points less than 125 degrees C and they also are greater than 25 degrees C apart

Question 8

fractional distillation

Answer 8

works best with compounds that have boiling points that are less than 25 degrees C apart

setup is the same as simple distillation with the addition of a fractionating column between the flask and condenser to provide a larger surface area on which the vapors of the distillated condense before distilling into the receiving flask

Question 9

vacuum distillation

Answer 9

appropriate for compounds that have a boiling point of greater than 150 degrees C

at that high of temperature, the compound may decompose when heated beyond 150 degrees C

so we decrease the pressure of the system and consequently lower the boiling point (due to Gay-Lussac’s Law)

Question 10

intramolecular bonding does what to boiling point

Answer 10

intrAmolecular bonding is within the same molecule and will decrease the boiling point

Question 11

intermolecular bonding does what to boiling point

Answer 11

intErmolecular bonding is between different molecules and the stronger the relationship, the higher the boiling point

Question 12

superheating

Answer 12

occurs when a liquid is heated above its boiling point but does not boil

surface tension can cause superheating because it can inhibit the formation of bubbles. As bubbles attempt to form, surface tension causes a local increase in vapor pressure that surpasses the ambient pressure, allowing the liquid to heat above its boiling point. This can cause large bubbles at the surface which can erupt violently and eject hot liquid

Question 13

boiling chips

Answer 13

made of nonreactive porous material and provides nucleation sites (divots on the surface) where small bubbles of vapor can form

helps avoid superheating by allowing the liquid to boil evenly