PRELIM 1

Question 1

why do impurities lower melting point

Answer 1

they increase disorder in a lattice structure (increase ∆S which decreases T melting)

Question 2

why do impurities broaden melting point range

Answer 2

earlier detection of melting point, impurities have different melting points

Question 3

list purity techniques

Answer 3

TLC (count # spots), melting point (assess range), recrystallization (remove impurities at different temperatures), extraction (remove unwanted layers)

Question 4

list separation techniques

Answer 4

TLC, column chromatography, extraction, heating

Question 5

list identification techniques

Answer 5

melting point, IR, TLC (comparisons to standard)

Question 6

stationary phase

Answer 6

silica, polar because hydrogen bonding

Question 7

what compounds can bind to stationary phase (and have what element)

Answer 7

polar compounds, extra H’s

Question 8

mobile phase

Answer 8

less polar, moving via capillary action

Question 9

iodine vapors dip

Answer 9

makes brown spots

Question 10

olefin dip (potassium permanganate)

Answer 10

makes yellow/brown against purple

Question 11

when to use olefin dip

Answer 11

oxidizable (remove H from carbon) alcohol, aldehyde, alkene, alkyne

Question 12

phosphomolybdic acid dip

Answer 12

universal green/brown spots

Question 13

p-anisaldehyde

Answer 13

various colors against pink

Question 14

when to use p-anisaldehyde

Answer 14

nucleophiles, oxygenated compounds (have an O)

Question 15

what does increasing polarity of solvent do to Rf

Answer 15

increases RF

Question 16

define partition coefficient

Answer 16

ratio of concentrations of compounds in mixture of 2 immiscible solvents at equilibrium

Question 17

increasing Kc of octanol to water = ?

Answer 17

increase across blood-brain barrier

Question 18

Lipinskin’s rule of 5

Answer 18

likelihood drug is orally bioavailable

Question 19

extraction

Answer 19

compound of interest moves layers

Question 20

washing

Answer 20

compound of interest stays in layer

Question 21

increasing steps of extraction =

Answer 21

increased mass of compounds in organic layer and increased surface area

Question 22

recrystallization relies on..

Answer 22

Ksp and differential solubilities of contaminants and target compounds AND/OR different amounts of impurities and compound

Question 23

when does recrystallization work best

Answer 23

if starting material is relatively pure

Question 24

solvent of recrystallization

Answer 24

high temperature coefficient
at high temp: dissolve most compound, impurities insoluble
at low: dissolve little compound (is crystals), impurities soluble

Question 25

why cool slowly in recrystallization

Answer 25

if fast, it traps impurities in the crystals by fast precipitation

Question 26

why no evaporating on hot plate

Answer 26

can set organic vapors that are denser than air on fire

Question 27

what does heating mantle do

Answer 27

heats; no thermostat

Question 28

what does voltage regulator do

Answer 28

control heat

Question 29

why heating mantle elevated using wood

Answer 29

need to remove heat easily by lowering it

Question 30

water in is at the ___ and water out is at the ___ (reflux)

Answer 30

bottom, top

Question 31

steam is in at the ___ and water is out at the ___

Answer 31

top, bottom (if not, flood)

Question 32

eutectic point

Answer 32

ratio of compounds in a mixture that elicits the lowest melting point for that mixture

Question 33

is H2O or OH- a better leaving group

Answer 33

H2O because weaker base; accepts electrons better

Question 34

oxidation

Answer 34

increasing bonds to oxygen; decreasing bonds to hydrogen

Question 35

reduction

Answer 35

decreasing bonds to oxygen; increasing bonds to hydrogen