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What Is Distillation? - Definition, Process & Apparatus

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  • 0:01 Definition of Distillation
  • 0:38 Distillation Process
  • 2:05 Distillation Apparatus
  • 3:10 Separating Compounds
  • 3:46 Lesson Summary
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Lesson Transcript
Instructor: Roger Harris
Explore distillation, the chemist's most useful method for separating substances dissolved in liquids. We cover the cycle of vaporization, cooling, and condensation that is the basis for the process. You will also learn what laboratory apparatus you need to perform the procedures involved.

Definition of Distillation

Have you ever admired the shapes of clouds? Clouds form when water vapor in the atmosphere rises and meets cool air. The cool air causes the water to then condense into droplets. The same process of condensation is at work during distillation, which is essentially when a liquid is purified through temperature changes.

The condensation that results when a warm vapor cools is a key process in distillation. You might have also heard of distillation as the method to produce alcoholic spirits. In chemistry (which is what we're really talking about here), it can really be any liquid, as the definition earlier suggested.

Distillation Process

The process of distillation begins with heating a liquid to boiling point. The liquid evaporates, forming a vapor. The vapor is then cooled, usually by passing it through pipes or tubes at a lower temperature. The cooled vapor then condenses, forming a distillate. The distillate is a purified form of the original liquid. When the liquid evaporates, many impurities are left behind, so they are not present in the distillate.

Chemists use distillation to purify compounds in solution or to separate mixtures of solutes. For example, different compounds have different boiling points. This property means that a more volatile compound will evaporate at a lower temperature than a less volatile compound.

Let's look at it this way: imagine you have a mixture of two compounds. If these compounds have different boiling points, you can separate them using distillation. The process takes advantage of substances readily changing their 'states of matter' from a liquid phase to a gas phase and back to a liquid phase again.

The key step is to raise the temperature of the mixture to a point above that of the compound with the lower boiling point. But you also have to make sure it's below that of the compound with the higher boiling point. The compound with the lower boiling point will then evaporate, leaving behind the compound with the higher boiling point. If the vapor is then condensed, you're only going to have the compound with the lower boiling point, since you separated the two compounds. Simple, right?

Distillation Apparatus

Given this process, you'd be correct in thinking that a variety of apparatuses are needed to carry out distillation. The basic apparatus includes a retort stand. A ring support is clamped to the stand. A round-bottomed flask sits on the ring support. This distilling flask contains a liquid that is heated from underneath by a Bunsen burner. A thermometer sits in the neck of the flask to allow monitoring of the vapor temperature. The thermometer allows the temperature of the vapor to be controlled to correspond with the boiling point of the desired component in the heated liquid.

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