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Methods of Separation
Procedure & Concept Guide
by David Arrow
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Lab Procedures
Methods of Separation
A. Filtration
D. Distillation
F. Separatory Funnel
G. Electrolysis
* Some of the above links require an internet connection
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Ring Stand
This stand can be used with a ring clamp (for filtering or heating beakers) of a clamp for holding test tubes.
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Funnel
Funnel made of plastic (glass funnels are also available). Used for holding filter paper when filtering (see next few slides).
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Filter Paper
Filter paper is used to separate a solid from a liquid. It comes with different sized pores. The paper with smaller pores will filter out more particles, but also takes longer for the liquid to pass through the paper.
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Filter Paper
1. Fold filter paper in half
2. Fold filter paper in half again
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3. Pull back one ply of the paper so that it forms
a cone shape.
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Filtering Set-up
1.Placefoldedfilterpaperinfunnel
2.Placefunnelinringstand
3.UseErlenmeyerFlasktocatchfiltrate
4.Adjustheightofringclampsothatfunneltipisinsideofflask
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Filtering Set-up
5. Slowly pour in solution to be filtered
6. Try to only pour in liquid, keeping most of the solid out of filter.
7. Do not allow liquid level to reach above edge of filter paper.
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Filtering Video (requires Internet)
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If video does not play, click here or go to https://www.youtube.com/watch?v=jbVxg8SFY38
Centrifugation
A centrifuge is a device used to separate mixtures. The sample is spun at high speeds until the components of the mixture form distinct layers in the vial.
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Blood Before
Centrifugation
Blood After
Centrifugation
Centrifugation
A centrifuge is effective when the mixture you are separating contains substances with different densities, such as a solid dispersed in a liquid. Such as separating…
• the pulp from orange juice
• cream from raw milk
• blood cells from plasma
At above right, you see plasma layer and separate, dark colored blood cell layer after centrifugation
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Centrifugation
Blood Sample
Plasma
White Blood Cells
The centrifugal force exerted by the spinning causes the more dense substances to be pulled to the outside (bottom) of the tube, while the least dense substances remain at the top
Red Blood Cells
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Centrifugation
A Follow this link to watch a video of centrifugation
Note: You must be connected to the internet to view this video
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Paper Chromatography
In paper chromatography, a liquid mixture is separated by placing some absorbent paper containing a small sample of the mixture in a solvent. As the solvent rises up the paper by capillary action, the mixture is separated into its different components
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Paper Chromatography
4
Absorbent
Paper
Those most attracted to solvent rise up the farthest
Chromatography works because the different substances in the mixture (ink) have different levels of attraction to the solvent.
3
Less attracted inks “fall out” sooner
2
Inks in mixture are attracted to solvent
1
Solvent rises up paper due to capillary action
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Paper Chromatography
Paper chromatography can be used to separate a mixture containing at least some polar compounds.
There must be a significant difference in the polarity of the substances in the mixture you are trying to separate. This assures that there will be a difference in the attraction to the solvent.
There are many different types of chromatography that are commonly used in analytical labs to analyze and identify samples.
Paper chromatography is often used to separate inks or pigments in a mixture, but is also used to separate amino acids or to determine the presence of certain drugs or hormones in a sample.
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Paper Chromatography
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If video does not play, click here or go to https://www.youtube.com/watch?v=3ZP_E0eTmMU
Extraction by Separatory Funnel
A separatory funnel can be used to separate two immiscible liquids. Liquids are generally immiscible if one is polar and the other is nonpolar.
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Extraction by Separatory Funnel
Since the layers don’t mix, you will be able to see a dividing line between the two liquids.
Since you can see the division, use the funnel to drain one liquid out first and leave the other.
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Extraction by Separatory Funnel(Internet Required)
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If video does not play, click here or go to https://www.youtube.com/watch?v=2TNZZxzKiZk
Distillation
Distillation is a process that can be used to separate 2 liquids that are mixed together. In the example pictured, a mixture of liquid ethanol and water are being separated.
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Distillation
The mixture of liquids is
heated until one begins to boil
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Distillation
The mixture of liquids is
heated until one begins to boil
In this case, the ethanol
begins to boil when the temp
gets to 78º C
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Distillation
The mixture of liquids is
heated until one begins to boil
In this case, the ethanol
begins to boil when the temp
gets to 78º C
As more heat is added, the
Temp stays at 78 º C while all
of the ethanol evaporates and
the water all remains as liquid
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Distillation
Cold water is run through
a double-wall
condensation tube
When the ethanol vapor hits
The cold wall of the tube,
It condenses back into liquid.
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Distillation
Only
Waer
The original flask will contain
only water and all of the ethanol
will be in the collection beaker
Ethanol
When the bubbling stops
and the temp starts to rise, the
Distillation is complete
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Distillation
Distillation is used when separating a mixture of 2 miscible liquids that have significantly different boiling points
Antifreeze is a mix of ethylene glycol and water
Ethylene glycol & water
Acetone boils at 56ºC , so it boils well before water
Ethylene glycol boils at 197 ºC, so water boils off first, & Ethylene glycol is left
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Distillation
Note the differentboiling points of each substance
Distillation is used to separate crude oil into its many different components
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Distillation Video (Internet required)
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If video does not play, click here or go to https://www.youtube.com/watch?v=74rOJ1GFbC0
Electrolysis
Electrolysis of Water
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Some compounds can be separated into the elements by passing electricity through them. This process is know as electrolysis.
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Electrolysis
When electricity is passed through a conducting substance, the energy from the electricity can break apart the chemical bonds.
In this picture, sodium chloride, NaCl, is being broken down into sodium and chlorine
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Cl
Na
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Electrolysis - https://www.youtube.com/watch?v=i9xS9t-KMpc
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In the video, you are seeing lead bromide being broken down chemically into lead and bromine
Lead bromide Lead + Bromine
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Crystallization
A solid solute dissolved in a liquid can often be separated by crystallization. In this process, the liquid is allowed to evaporate, leaving the solid behind crystallized on the container.
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Crystallization - https://www.youtube.com/watch?v=-fGD4NHgp6c
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The video is a time lapse photagraphy of saltwater evaporating. Only the water evaporates, leaving the salt behind. Note the cubic shape of the salt crystals as they form.
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Crystallization
Crystallized
Solid
(on inside surface
of flask)
Note that the crystallized solid is usually “stuck” to the container and is difficult to scrape out. In a quantitative lab, the flask mass is first measured empty, then the flask is measured after crystallization (with crystals in it). The difference between the 2 is the crystal mass.
MassCrystals = Massflask+crystals - Massflask
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The End!
Methods of Separation
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Miscibility -
Liquids are said to be “miscible” if they mix together to form a homogeneous solution.
“Ring”
dividing
layers of
2 liquids
Ethanol & Water Mix
completely
Miscible
Immiscible
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Polarity -
A molecule is polar if it has a positive side and a negative side
What is a Polar Bond?
δ-
Negative Side
Electrons are evenly spread
(no build-up of
electrons anywhere)
O
H
H
Water
Positive Side
δ+
F
F
δ+
“Ring”
Negative Side
(build-up of
electrons on
this end)
δ-
δ+
H
F
No positive or negative end
Positive Side
(loss of
electrons on
this end)
Nonpolar
Polar
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Differences in electronegativity and shape determine if the electrons in a molecule are spread evenly or not. If they are evenly spread, the molecule is nonpolar. If they “get pulled” to one side, it is polar.
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Capillary Action -
Refers to a liquid rising up a narrow tube-like space to due to an attraction to the tube
“Ring”
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Adhesion
- how strongly a
substance is attracted
to another surface
Cohesion
- how strongly a
substance is
attracted to itself
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“Higher polarity means higher rising” - the more polar the molecule it is, the more it will be attracted to a tube with charges. Therefore, the higher it will rise up the tube.
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