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Acid-Base Extraction: Theory, Purpose & Procedure

Acid-Base Extraction: Theory, Purpose & Procedure
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  • 0:03 Acid-Base Extraction…
  • 0:53 Acid-Base Extraction Purpose
  • 1:28 Acid-Base Extraction Theory
  • 2:25 Acid-Base Extraction Procedure
  • 5:02 Lesson Summary
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Lesson Transcript
Instructor: Korry Barnes

Korry has a Ph.D. in organic chemistry and teaches college chemistry courses.

The focus of this lesson will be on learning the purpose, theory, and procedure behind separating organic acids and bases from one another when they are present together as a mixture.

Acid-Base Extraction Background

Mark just arrived for his weekly organic chemistry lab and today his instructor has informed the class that they will be given a mixture of an organic acid, a base, and a neutral compound. Their task for the day will be to separate and isolate the acid, the base, and the neutral from one another and get them in pure form. How can Mark do this? He's beginning to feel nervous and a bit apprehensive about the experiment because he doesn't really know how he's supposed to separate the different components from the mixture.

The experiment Mark and his classmates will be working on is very common in the organic chemistry lab, and is called an acid-base extraction. The idea is to leverage the acid-base properties of the compounds in the mixture to help separate them from one another. Let's come along with Mark and help him work through his project for the day!

Acid-Base Extraction Purpose

Let us get started by briefly discussing the purpose behind an acid-base extraction. A lot of times organic compounds exist as complex mixtures, and the different components of the mixture must be separated from one another. For instance, when natural products are isolated from plant and marine sources, a lot of times one step in the process involves utilizing an acid-base separation technique. It's a great way to separate and group organic compounds together that contain the same functional groups. In this method, acids, bases, and neutral compounds can be separated and pooled together.

Acid-Base Extraction Theory

The idea behind an acid-base extraction is to utilize the acid-base properties of organic compounds and selectively isolate them from one another when they're present in a mixture. In organic chemistry, acids are known as carboxylic acids and contain the -COOH functional group. Bases contain at least one nitrogen atom and are commonly called amines. When the acid-base mixture is treated with aqueous sodium hydroxide (a base), it will react only with the carboxylic acid in the mixture, forming a water-soluble salt which can be separated later. Neutral organic compounds don't have properties of either acids or bases.

If the mixture is treated with aqueous hydrochloric acid, it will react with the amine in the mixture, again forming a water-soluble salt that can be separated later. So really, we are just leveraging each component's ability to react with either sodium hydroxide or hydrochloric acid to allow us to isolate them from one another.

Acid-Base Extraction Procedure

So how does Mark and the class go about conducting an acid-base extraction experiment? If a few simple steps are followed, anyone can do this with confidence!

Step One: Preparation of the Mixture

The first thing we must do is to dissolve the unknown mixture in some sort of organic solvent. We need an organic solvent that is immiscible (won't mix) with water, so we can separate out the different components. Common solvents that are used for this type of procedure include chloroform, diethyl ether, and dichloromethane. The choice of the organic solvent doesn't really matter, providing it will dissolve all of the components in our mixture (the carboxylic acid, the amine, and the neutral compound).

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