Intensive General Chemistry

Chemical separations I

Isabelle Vu Trieu ilv2@columbia.eduhttp://ull.chemistry.uakron.edu

What is a distillation?

This a separation technique for purifying a liquid.

In this process, the liquid is heated to the boiling point and vaporized.

That vapor is then cooled and recondensed in the liquid form

Origin of distillation

Partition

Phase 1

Phase 2

A A A

A

A

A

A

AAA

A

Partition constant: K = aA(phase 2)/ aA(phase 1)

Ideal solutions

Solutions are ideal when the intermolecular interactions among species are identical

An ideal solution obeys Raoult’s law

PA = XA PAo

Raoult’s Law applied to mixtures

Relative volatility or RV

Relative Volatility or RV

Phase diagram

In the distillation process, the vapors get enriched in the more volatile component

In the distillation process, the vapors get enriched in the more volatile component

Fractional distillation: numerous evaporation-distillation stages

Distillation columns

Distillation set-up

Introduction to chromatography

Chromatography is a separation technique based on partition between a mobile phase and a stationary phase.

Invented by a botanist (M.Tswett) at the beginning of the 20th century

From greek chroma:”color” and graphein:”write”

Introduction to chromatography

Phase 1

Phase 2

A A A

A

A

A

A

AAA

A

Partition constant: K = aA(stationary)/ aA(mobile)

Mobilephase

Stationaryphase

Column Elution

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Column Elution

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Thin Layer Chromatography (TLC)

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are needed to see this picture.

Pre-lab questions

Find out the flash point and the auto-ignition temperature of cyclohexane and toluene.

What is the meaning of these temperatures? In the distillation part, what is the role of

the stainless steel sponge?