Chromatology: videos Flashcards
Define chromatography
Method of analyzing and purifying organic compounds based on polarity differences
passing a mixture which contains
Name the separation and purification techniques
extraction distillation chromatography recrystallization
why do polar molecules stay at bottom of plate
polar molecules capable of H bond interactions with silica and gets retained
What is column chromatography
mixture of three compounds: ferrocene, acetyl ferrocene, diacetly ferrocene (iron added for color)
Compare mobile and stationary phase
compounds to be separates dissolved in a mobile phase (some solvent) through a stationary phase (ex silica) which separates them based on differences of adsorption to the stationary phase
describe process of thin layer chromatography
uses thin plastic or glass trays coated w adsorbent to identify the composition of pigments, chemicals, or other unknown substances, small amounts
describe process of column chromatography
uses column filled with adsorbent to separate larger scale mixtures of compounds
In TLC mobile phase travels ___ in CLC mobile phase travels ___
up
down
A distribution equilibrium forms when a compound is either dissolved in a mobile phase or adsorbed in a stationary phase
true
The longer the mobile phase travels, the better the separation between A and B
true
stationary phases are usually very polar, while mobile phases vary widely in polarity
true
If cmpd B spends more time in mobile phase than compound A, B will move further along the direction of flow than A and will eventually be separated in space from A
true
In TLC, silica fel and alumina are the most common solid adsorbents
true
How does UV light detection work in TLC?
cmpds containing benzene rings or conjugated systems usually absorb light in IV region of electromagnetic spectrum.
HOw does chemical staining with idodine work?
non destructive
few crystals of iodine placed in closed chamber collect iodine on the spots by weak electrostatic attraction
will form yellow or brown complex except for saturated hydrocarbons or alklyl halides
TLC analysis yields an Rf value of less than 0.10 for the cmpd to be separated. How should the mobile phase be modified to increase Rf value?
increase polarity of solvent by using more ethyl acetate
What is column chromatography
technique for purification of synthetic or natural products by polarity differences
variety of adsorbents can be used as stationary phase, silica gel most common(very poalr)
alumina is also used
The adsorbent is applied to column in two ways which are
slurry/wet packing
dry packing
loading sample, wet application
dissolve sampl ein small amount of initial mobile pahse and apply by long pipette to top of column
drain eluent from column until no sample remains above surface of sand. Good method but in many cases samples not soluble in initial mobile phase
True or False: chromatography involves a mobile and stationary phase
truen
true or false: non polar molecules will have a low Rf
false
true or false: mobile phase is often a mixture of polar and nonpolar organic solvents
true hexane/ethyl acetate
a student develops a TLC of green food dye. After 12 minutes the solvent moved up 10cm and blue spot has advanced 6 cm from origin. After 14 mins the solvent moved a further 5 cm. How far will blue be from origin?
you can ignore the time
Rf=Y/X 6cm/10cm= 0.6
x/(10+15)=?
0.6/10cm=X/15
X=9cm
while eluting the sample, add more solvent as necessary. Always start with a less polar solvent, slowly increasing polairty
true
