Assume you have a mixture of naphthalene and benzoic acid...

Key Concepts

Acid-Base Extraction

Acid-base extraction is a separation technique that leverages the differences in solubility between the protonated (acidic) and deprotonated (basic) forms of a compound. Adjusting the pH of the solution can thus be used to selectively partition one component into a different solvent, facilitating its isolation from a mixture.

Selective Solubility

Selective solubility involves the inherent variation in solubility of substances based on their chemical properties. By modifying environmental conditions such as pH, the solubility of specific components can be altered, making it possible to separate substances effectively based on their differential solubility in different phases.

Acid-Base Chemistry

This concept centers around the principles of proton donation and acceptance, which enables selective reactions such as protonation and deprotonation. By understanding acid-base behavior, one can manipulate the chemical form of a component, significantly altering its reactivity and solubility.

Transcript

00:02 This is the answer to chapter 20, problem number three from the mcmurray organic chemistry textbook.

00:09 This problem is a very common organic laboratory problem.

00:16 So if you're taking an organic chemistry course and it has a laboratory component, this is very often the first or second lab that's conducted in the semester.

00:27 So this problem says, assume you have a mixture of naphthalene and benzoic acid that you want to separate.

00:32 How might you take advantage of the acidity of one component in the mixture to affect a separation? okay, so we have a mixture of these two solids.

00:43 They're both just white powders.

00:46 So when they're mixed together, they're impossible to physically separate.

00:52 So what we're actually going to do is what's known as an acid -based extraction.

00:57 So benzodia acid, obviously, is an acid.

01:00 Naphthalene, you know, when you look at it, it's, totally aromatic.

01:04 It doesn't really have any functionality beyond its aromaticity.

01:08 And so we're going to have to do something that takes advantage of the acidity of benzodiaic acid.

01:17 And so basically, the first thing that we would do would be to dissolve both of these solids into an organic solvent.

01:28 So dissolve into, i don't know, let's say, ether.

01:37 Into et2o, so diethyl ether.

01:41 And then once these two solids are dissolved into the ether, what we're going to do is actually add some aqueous base.

01:51 So let's say aqueous sodium hydroxide.

01:58 So a nice strong base.

02:01 And so that's going to deprotonate the benzoic acid.

02:04 So after the addition of aqueous sodium hydroxide, what we will have will be this.

02:15 So the naphthalene is going to be unaffected.

02:21 So it's going to look exactly the same as it did.

02:26 But the benzoic acid is actually going to be in the form of the benzodiae ion.

02:32 So it will look like this.

02:38 So it's been deprotinated.

02:42 And it will be associated with the positive sodium ion...

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