2.3 Separating the Substances in
a Mixture
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•
•
•
Separating Mixed Substances
Types of Separation
Mechanical Means of Separation
• Density Separation
• Centrifugation
Non-Mechanical Means of Separation
• Chromatography
• Distillation
• Froth Flotation
2.3 Separating the Substances in
a Mixture
Separating Mixed Substances
Most naturally occurring objects and materials are mixtures.
The trick to separating the substances in a mixture is to pick a property that
clearly differentiates the substances.
Laboratory separations are performed to allow the substances in the mixture
to be identified. Industrial scale separations are performed to obtain the
target substances for their useful properties, their intrinsic values, or to use
the substances to produce useful mixtures of our own design.
text page 86
2.3 Separating the Substances in
a Mixture
Types of Separation
Separation
Physical Separations
Chemical Separations
2.3 Separating the Substances in
a Mixture
Types of Separation
Chemical Separations
those separations involving a chemical reaction
Physical Separations
those separations not involving a chemical reaction
text page 86
2.3 Separating the Substances in
a Mixture
Types of Separation
Separation
Physical Separations
Chemical Separations
2.3 Separating the Substances in
a Mixture
Types of Separation
Separation
Physical Separations
Mechanical
Chemical Separations
Non-Mechanical
2.3 Separating the Substances in
a Mixture
Types of Separation
Mechanical Separations
use contact forces, gravity, or motion to separate the mixture’s
components
Non-Mechanical Separations
use heat, electricity, magnetism, dissolving, or sticking to separate the
mixture’s components
text page 86
2.3 Separating the Substances in
a Mixture
Mechanical Means of Separation
Separation
Physical Separations
Mechanical
Non-Mechanical
e.g. density separation
e.g. centrifugation
Chemical Separations
2.3 Separating the Substances in
a Mixture
Mechanical Means of Separation
Density Separation
Density separation can be used to separate solids with different
densities.
If you add a liquid that is more dense than only one of the solids then
only that solid will float while the others will sink. Conversely, if you
add a liquid that is less dense than only one of the solids then only that
solid will sink while the others will float.
The particles that float can be skimmed off the top of the liquid and
dried. The particles that sediment can be separated from the liquid by
decanting off the liquid or by filtering out the sediment.
text page 87
2.3 Separating the Substances in
a Mixture
Mechanical Means of Separation
Centrifugation (Spinning)
Centrifugation enhances density separation. Particles that would normally
sink or rise still do so, just more rapidly. Centrifugation also causes
colloid particles, that would otherwise remain suspended, to sink or rise
according to their density.
Particles continue to travel in a straight line while the centrifuge tube
turns. The densest particles, having the greatest inertia (resistance to
change in motion), are selectively directed to the bottom of the tube.
text page 88
2.3 Separating the Substances in
a Mixture
Non-Mechanical Means of Separation
Separation
Physical Separations
Mechanical
Chemical Separations
Non-Mechanical
e.g. chromatography
e.g. distillation
e.g. froth flotation
2.3 Separating the Substances in
a Mixture
Non-Mechanical Means of Separation
Chromatography
Chromatography separates the substances in a solution by having a mobile
phase (a flowing liquid or gas) carry them at different rates through a
stationary phase.
Each substance travels through the stationary phase at its own
characteristic rate according to how well it dissolves in the mobile phase
and how well it adheres to the stationary phase.
text pages 88-90
2.3 Separating the Substances in
a Mixture
Non-Mechanical Means of Separation
Distillation
Distillation is any process that separates a mixture of substances by using
their different vapour pressures or boiling points.
Dissolved solids can be separated from their solvent by simple
distillation. Mixtures of liquids are separated by a method called
fractional distillation in which the simple distillation (vaporizing and
condensing) is repeated many times within the one device. The component
liquids proceed at different rates up the fractionating column so the
mixture becomes increasing richer in the liquid with the lower boiling
point as you move higher up the column.
text pages 90-91
2.3 Separating the Substances in
a Mixture
Non-Mechanical Means of Separation
Froth Flotation
Froth flotation is a process used to separate insoluble particles that repel
water to different extents.
In the mining industry, the target mineral is separated from the remainder
of the crushed ore by adding an oil that adheres only to the mineral grains
and then bubbling air through the mixture which floats the hydrophobic
mineral grains to the surface.
text pages 91-92