CHROMATOGRAPHY
Read the information below. Video links and questions appear throughout.
Watch the videos and answer the questions in the order in which they appear.
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Chromatography refers to certain processes by which the components or parts
of a mixture are separated. Such separations are of great value to the
analytical chemist because they permit him/her to separate, isolate, and
identify parts of a mixture that might otherwise be difficult to analyze.
The separation can be used for example, to detect drugs in animals or humans,
to determine the purity of food, or to analyze organic mixtures such as
fragrances.
There are several different metods of chromatographic separation, but all of
the rely on the fact that solubility is a unique property of a substance meaning
no two substances have exactly the same solubility in a particular solvent.
Also, the solubility of one substance is different in different solvents.
Most chromatographic separations utilize the property of adsorption.
Adsorption is the concentration of a gas, liquid, or solid on the surface of a
solid or a liquid. For example, activated charcoal is an effective filter because
of its ability to adsorb undesirable gases onto its surface.
Q1: Define chromatography
Q2: What does chromatography permit a chemist to do
Q3: List 3 uses for chromatographic separations
a)
b)
c)
Q4: What 2 properties of a substance are important in chromatography
a) ____________________
b) ___________________
Q4a: Why is activated charcoal useful
All chromatographic separations involve 2 phases: a fixed, or stationary, phase
and a moving, or mobile, phase. The fixed phase could be a sheet of porous paper
or a metal column. The fixed phase is often called the adsorbent. The moving
phase is a solvent-either a liquid or a gas. Other names for the moving phase
include eluent, solvent or solvent system. The moving phase consists of a solvent
or combination of solvents, in which the parts of the mixture to be separated are
soluble. Some solvents commonly used as a moving phase are water, alcohol,
benzene, and acetone.
Q5. What is the fixed phase in paper chromo ____________, and in gas chromo
_______________
The separation of the mixture begins when it dissolves in the moving phase.Due
to differences in their solubilities AND in their attraction to the fixed phase, the
parts travel at different rates along the fixed phase. At various points along the
paper or the column, parts leave the moving phase and become attached to the
fixed phase:
Some of the parts of the mixture are adsorbed more readily to the fixed phase
than other parts and as such are “held back” on the paper or in the column.
Compounds adhere to the stationary or fixed phase due to dipole interactions
such as Hydrogen Bonding, dispersion forces, or ionic interactions.
At the same time, some of the parts of the mixture are more soluble in the
moving phase than others and move with that phase “away” from the other parts
of the mixture.
Q5a. WHY would a substance adhere to the fixed phase