Separation of Mixtures
Ms. Grobsky
Separating Mixtures
 Remember, substances in a mixture are physically
combined
 So, processes that are based on differences in physical
properties can be used to separate individual components
of the mixture
 Physical properties include:
 Odor
 Color
 Volume (size)
 Physical state
 Density
 Melting point
 Boiling point
 Solubility
 Different techniques are used to separate mixtures into
individual components
Filtration
 Separates heterogeneous mixtures
composed of an insoluble
substance and a soluble substance
 Uses a porous barrier to separate
the solid from the liquid
Mixture of
solid and
liquid
Stirring
rod
Funnel
Filter paper
traps solid
 Liquid passes through, leaving the
solid in the filter paper
Filtrate (liquid
component
of the mixture)
Filtration
Distillation
 Used to separate homogeneous
mixtures with liquids that have
different boiling points of the
components
 In the process, the mixture is
boiled
 The liquid with the lower boiling
point will vaporize first and the
vapor is collected and condensed
 The liquid collected is the
distillate
 Gasoline, kerosene, fuel oil, and
lubricating oil are produced from
petroleum by distillation
A Distillation Apparatus
How to Separate a Sand-Salt
Water Mixture
Evaporation and Crystallization
 Technique that can be used to
separate a solute from the
solvent in a solution
 Results in the formation of
pure solid from a solution
containing dissolved particles
of that substance
 As the liquid evaporates, the
dissolved substance comes
out of solution as crystals
 Produces highly pure solids
 Rock candy is an example of
this!
Using a Separatory Funnel
 A separating funnel can
be used to separate two
liquids which are
immiscible
 The more dense liquid
can be collected first
by opening the
stopcock
Centrifugation
 Can be used with liquid or
solid mixtures
AFTER
Before
 Spin sample very rapidly
 Denser materials go to bottom
 Example
 Separate blood into serum and
plasma
Serum
Blood
 Serum (clear)
 Plasma (contains red blood cells
‘RBCs’)
 Check for anemia (lack of iron)
RBC’s
A
B
C
Magnetism
Can be used to separate
a magnetic substance
from a non-magnetic
substance
Magnets are used in the
recycling industry to
separate iron and noniron metals
Chromatography
 Broad category of separation techniques for obtaining pure
substances from homogeneous mixtures like dyes, ink, gas
mixtures, drug analysis or even DNA!
 Some chromatography techniques are low-tech
 Paper chromatography
 Whereas others are more high-tech and expensive
 Ion exchange chromatography
 HPLC chromatography
 Gas chromatography
 Each technique differs in their mobile and stationary phases
 Stationary phase
 The platform on which chemicals are separated
 Mobile phase
 Solvent that carries the chemicals through the stationary phase
Separation by Gas
Chromatography
sample
mixture
a chromatographic column
stationary phase mobile phase
selectively absorbssweeps sample
components
down column
http://antoine.frostburg.edu/chem/senese/101/matter/slides/sld006.htm
detector
Separation by
Chromatography
sample
mixture
a chromatographic column
stationary phase mobile phase
selectively absorbssweeps sample
components
down column
http://antoine.frostburg.edu/chem/senese/101/matter/slides/sld006.htm
detector
Ion Chromatogram of
Orange Juice
detector
response
K+
Na+
0
5
Mg2+ Fe3+
10
15
time (minutes)
Ca2+
20
25
How Does Chromatography
Work?
Separation is based on different
substances having differences in
physical properties like:
Solubility of the sample in the mobile
phase
“Like Dissolves Like”
Molecule size
Separation occurs because various
components travel at different
rates
Taking a Closer Look at Paper
Chromatography
Paper chromatography is one easy
technique used to separate the
soluble components of a
homogeneous mixture
We will perform paper
chromatographic separations of the
pigments in FD&C dyes next class!
A Brief Overview of Paper
Chromatography
• Compound is placed on stationary phase
• Mobile phase passes through the stationary
phase
• Mobile phase solubilizes the components
• Mobile
phase
carries
the
individual
components a certain distance through the
stationary phase, depending on their
attraction (affinity) to both of the phases
Paper Chromatography
Mark the solvent
front & allow
paper to dry
Solvent
front
Purple spots
develop located at
different distances
from the origin line
Dye Spots
origin
solvent
Illustration of Chromatography
Stationary
Phase
Separation
Mobile
Phase
Mixture
Components
Components
Affinity to Stationary
Phase
Affinity to Mobile
Phase
Blue
----------------
Insoluble in Mobile Phase
Black


Red


Yellow

        
The Rf Value and How It’s Used

The chromatogram can be analyzed by measuring the
distance travelled by the solvent front, and the
distance from the origin to the center of each spot

This is used to calculate the Rf (relative front) value
for each spot:
Distance moved by spot
Rf 
Distance moved by solvent

An Rf value is characteristic of a particular solute in a
particular solvent

It can be used to identify components of a mixture by
comparing to tables of known Rf values
X
Rf 
Y
The Rf value is
always a value less
than one as the
solvent front always
moves further than
the solute molecules
X3
Y
X1
X4
X2
X5