• 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.

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2.3 Separating the Substances in a Mixture

Separation

Physical Separations Chemical Separations

Types of Separation

2.3 Separating the Substances in a Mixture

text page 86

2.3 Separating the Substances in a Mixture

Types of Separation

Physical Separationsthose separations not involving a chemical reaction

Chemical Separationsthose separations involving a chemical reaction

Separation

Physical Separations Chemical Separations

Types of Separation

2.3 Separating the Substances in a Mixture

Separation

Physical Separations Chemical Separations

Mechanical Non-Mechanical

Types of Separation

2.3 Separating the Substances in a Mixture

Mechanical Separationsuse contact forces, gravity, or motion to separate the mixture’s components

Non-Mechanical Separationsuse heat, electricity, magnetism, dissolving, or sticking to separate the mixture’s components

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2.3 Separating the Substances in a Mixture

Types of Separation

Mechanical Means of Separation

2.3 Separating the Substances in a Mixture

Separation

Physical Separations Chemical Separations

Mechanical Non-Mechanical e.g. density separation

e.g. centrifugation

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.

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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.

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2.3 Separating the Substances in a Mixture

Mechanical Means of Separation

Separation

Physical Separations Chemical Separations

Mechanical Non-Mechanical

2.3 Separating the Substances in a Mixture

Non-Mechanical Means of Separation

e.g. chromatography

e.g. distillation

e.g. froth flotation

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.

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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.

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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.

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2.3 Separating the Substances in a Mixture

Non-Mechanical Means of Separation