Ch.16 Amines

McMurry - Fundamentals of General, Organic, and Biological Chemistry 8th Edition

McMurry8th EditionFundamentals of General, Organic, and Biological ChemistryISBN: 9780134015187Not the one you use?Change textbook

McMurry 8th Edition

Ch.16 Amines

Problem 43

Chapter 16, Problem 43

Many hair conditioners contain an ammonium salt such as the following to help prevent 'fly-away' hair. These ions will react with neither acid nor base. Provide a reason why.

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Identify the structure of the ammonium salt in the hair conditioner. Ammonium salts are compounds containing a positively charged ammonium ion (NH₄⁺) or a derivative where one or more hydrogens are replaced by organic groups.

Understand the chemical behavior of ammonium salts. These salts are typically formed from the reaction of an amine (a weak base) with an acid, resulting in a stable ionic compound.

Explain why the ammonium ion does not react with acids. The ammonium ion (or its derivatives) is already in its protonated form, meaning it has accepted a proton (H⁺). Since acids donate protons, the ammonium ion cannot accept another proton and thus does not react with acids.

Explain why the ammonium ion does not react with bases. Bases accept protons, but the ammonium ion is already positively charged and stable. It does not readily lose a proton to react with a base under normal conditions.

Conclude that the stability of the ammonium ion in its ionic form makes it unreactive with both acids and bases, which is why it is suitable for use in hair conditioners to prevent 'fly-away' hair without undergoing chemical changes.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Ammonium Salts

Ammonium salts are ionic compounds formed from the reaction of ammonia with an acid. They typically consist of a positively charged ammonium ion (NH4+) and a negatively charged anion. In hair conditioners, these salts help to smooth hair by neutralizing static electricity, which can cause 'fly-away' hair.

Ionic Compounds and Solubility

Ionic compounds, like ammonium salts, are generally soluble in water due to the strong electrostatic forces between the ions. However, their solubility does not imply reactivity with acids or bases. The stability of the ammonium ion in these salts means they do not readily participate in acid-base reactions, which is why they remain neutral in such environments.

pH Neutrality

pH neutrality refers to a solution that is neither acidic nor basic, typically having a pH of around 7. Ammonium salts in hair conditioners do not alter the pH of the hair or scalp significantly, allowing them to condition without causing irritation or unwanted chemical reactions. This neutrality is essential for maintaining healthy hair and scalp conditions.

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Related Practice

Textbook Question

How do amines differ from analogous alcohols in (a) odor, (b) basicity, and (c) boiling point?

Textbook Question

Draw the structures of the ammonium ions formed when the amines in Problem 16.30 are treated with acid.

a. N-Methylpentylamine

b. N-Ethylcyclobutylamine

c. p-Propylaniline

Textbook Question

Which is the stronger base, trimethylamine or ammonia? In which direction will the following reaction proceed?

Textbook Question

Choline has the following structure. Do you think that this substance reacts with aqueous hydrochloric acid? If so, what is the product? If not, why not?

Textbook Question

Complete the following equations (hint: remember that a nitrogen with three groups bound to it has a lone pair and one with four does not):

Textbook Question

Complete the following equations. (Hint: Remember that a nitrogen with three groups bound to it has a lone pair and one with four does not)

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