Amine Reactions: Study with Video Lessons, Practice Problems & Examples

In acid-base reactions, amines act as weak bases, accepting protons (H⁺) from acids, resulting in the formation of ammonium ions. For example, methylamine reacts with hydrochloric acid, transforming into methylammonium ion. This process illustrates the Brønsted-Lowry definition, where the acid donates a proton, and the amine becomes positively charged by forming four bonds with nitrogen. Understanding these transformations is crucial for grasping the behavior of amines in various chemical contexts.

Acid-Base Reaction Concept 1

This video, we're going to take a look at amine reactions through the prism of acid-base reactions. Now under this type of reaction, an acid reacts with an amine, which represents a weak base. Now recall, when a base accepts an H+, it transforms into a conjugate acid. This conjugate acid of an amine is called the Ammonium ion. Now, here we're going to say for the Ammonium ion, we modify the ending of amine, which is the neutral form of our amine, to ammonium ion. So if we take a look here at this generic amine reaction, we have Methylamine as our starting amine, it's reacting with hydrochloric acid which is an acid. We know following the Brønsted definition that the acid donates an H+ to the base. So when it accepts that H+, it's now accepting an H+, so now nitrogen is making 4 bonds, so it's going to be positively charged. And we're going to say when a nitrogen is positively charged by making 4 bonds, that's when the moniker of Ammonium ion comes into play. So we're going from methylamine to methyl ammonium ion. Okay, so this would be the name of our newly created ammonium ion product.

Acid-Base Reaction Example 1

Predict the products formed from the following reaction between nitric acid and ammonia. Right. So nitric acid is our acid, ammonia is our neutral amine, so it's a weak base. Here, we're using the Bronsted-Lowry definition. We know that the acid donates an H⁺. So when that acid donates an H⁺, it forms a conjugate base, so it's going to form the nitrate ion, and then ammonia gains an H⁺ to become NH₄⁺, so it becomes the ammonium ion. In addition to this, notice that there is a solid arrow going forward because we have a strong species mixing with a weak species. Nitric acid is a strong acid, mixing with ammonia which is a weak base. When a strong species, acid or base is involved, we have complete formation of our products, so we have a solid arrow going forward. Okay? But in this particular example here, we're going to say our Nitrate ion and Ammonium ions are our products created between the reaction of nitric acid and ammonia.

Determine the ammonium ion formed in the following reaction between diethylamine and hydrobromic acid.

• A.
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• D.

Here’s what students ask on this topic:

What is the role of amines in acid-base reactions?

Amines act as weak bases in acid-base reactions. They accept protons (H⁺) from acids, resulting in the formation of ammonium ions. For example, when methylamine (CH₃NH₂) reacts with hydrochloric acid (HCl), it accepts a proton to form methylammonium ion (CH₃NH₃⁺). This process follows the Brønsted-Lowry definition, where the acid donates a proton, and the amine becomes positively charged by forming four bonds with nitrogen. Understanding this behavior is crucial for grasping the chemical properties and reactions of amines.

How does methylamine react with hydrochloric acid?

Methylamine (CH₃NH₂) reacts with hydrochloric acid (HCl) in an acid-base reaction. The hydrochloric acid donates a proton (H⁺) to the methylamine, which acts as a weak base. This results in the formation of methylammonium ion (CH₃NH₃⁺) and chloride ion (Cl^-). The reaction can be represented as:

${\mathrm{CH}3}_{\mathrm{NH}}+{H\mathrm{Cl}}_{}\to {\mathrm{CH}3}_{\mathrm{NH}}+{\mathrm{Cl}}_{}-$

What is an ammonium ion and how is it formed?

An ammonium ion is a positively charged ion (NH₄⁺) formed when an amine accepts a proton (H⁺) from an acid. In the context of methylamine (CH₃NH₂), when it reacts with hydrochloric acid (HCl), it accepts a proton to form the methylammonium ion (CH₃NH₃⁺). This process involves the nitrogen atom in the amine forming four bonds, resulting in a positive charge. The general reaction can be represented as:

${R\mathrm{NH}2}_{+}$

Why do amines form ammonium ions when reacting with acids?

Amines form ammonium ions when reacting with acids because they act as bases, accepting protons (H⁺) from the acids. This protonation increases the number of bonds nitrogen forms, resulting in a positively charged ammonium ion. For instance, when methylamine (CH₃NH₂) reacts with hydrochloric acid (HCl), it accepts a proton to form methylammonium ion (CH₃NH₃⁺). This transformation is essential for understanding the behavior of amines in various chemical reactions and contexts.

What is the Brønsted-Lowry definition of acids and bases?

The Brønsted-Lowry definition of acids and bases describes acids as proton donors and bases as proton acceptors. In this framework, an acid donates a proton (H⁺) to a base. For example, in the reaction between hydrochloric acid (HCl) and methylamine (CH₃NH₂), HCl donates a proton to CH₃NH₂, forming the methylammonium ion (CH₃NH₃⁺) and chloride ion (Cl^-). This definition helps in understanding the behavior of substances in acid-base reactions.