Question

Write a balanced equation for the ionization of each of the following amines in water: a. methylamine b. dimethylamine c. aniline

Short answer

Balanced ionization equations: a. CH3NH2 + H2O → CH3NH3+ + OH- b. (CH3)2NH + H2O → (CH3)2NH2+ + OH- c. C6H5NH2 + H2O → C6H5NH3+ + OH-

Step-by-step solution

- Understand Ionization of Amines in Water

When amines ionize in water, they accept a proton (H+) from water, leading to the formation of an ammonium ion (protonated amine) and hydroxide ion (OH-). The general reaction can be written as: Amine + H2O → AmineH+ + OH-

- Write Ionization Equation for Methylamine

The chemical formula for methylamine is CH3NH2. When it ionizes in water: CH3NH2 (aq) + H2O (l) → CH3NH3+ (aq) + OH- (aq)

- Write Ionization Equation for Dimethylamine

The chemical formula for dimethylamine is (CH3)2NH. When it ionizes in water: (CH3)2NH (aq) + H2O (l) → (CH3)2NH2+ (aq) + OH- (aq)

- Write Ionization Equation for Aniline

The chemical formula for aniline is C6H5NH2. When it ionizes in water: C6H5NH2 (aq) + H2O (l) → C6H5NH3+ (aq) + OH- (aq)

Key concepts

Ionization in Water

Ionization in water refers to the process where a molecule interacts with water, causing it to break up into ions. In the context of amines, when they dissolve in water, they interact with water molecules and accept a proton (H+). This results in the formation of two new ions: an ammonium ion (which is a protonated form of the amine) and a hydroxide ion (OH-). For example, when methylamine (CH3NH2) ionizes in water, it forms methylammonium ion (CH3NH3+) and a hydroxide ion:
CH3NH2 (aq) + H2O (l) → CH3NH3+ (aq) + OH- (aq).
Understanding this concept is crucial, as it helps us comprehend the behavior of amines in aqueous solutions.

Amines

Amines are organic compounds derived from ammonia (NH3) where one or more hydrogen atoms are replaced by carbon-containing groups. They are categorized into three types based on how many hydrogen atoms are replaced:

• Primary amines: One hydrogen replaced (e.g., methylamine CH3NH2)
• Secondary amines: Two hydrogens replaced (e.g., dimethylamine (CH3)2NH)
• Tertiary amines: Three hydrogens replaced

Amines can act as bases due to the presence of a lone pair of electrons on the nitrogen atom, which can accept protons (H+). This is fundamental to their behavior in water, contributing to their ionization.

Balanced Chemical Equations

A balanced chemical equation ensures that the number of atoms for each element is the same on both sides of the equation. For the ionization of amines in water, here are the balanced equations:
1. For methylamine: CH3NH2 (aq) + H2O (l) → CH3NH3+ (aq) + OH- (aq)
2. For dimethylamine: (CH3)2NH (aq) + H2O (l) → (CH3)2NH2+ (aq) + OH- (aq)
3. For aniline: C6H5NH2 (aq) + H2O (l) → C6H5NH3+ (aq) + OH- (aq)
The balancing process involves ensuring the same number of each type of atom on both sides, reflecting the conservation of mass. This is achieved here by having one molecule of water producing one hydroxide ion and one protonated amine molecule, making the equations straightforward.

Protonation

Protonation is the process where a molecule gains a proton (H+). In the case of amines in water, protonation leads to the formation of an ammonium ion. For example, when methylamine (CH3NH2) is protonated, it becomes methylammonium ion (CH3NH3+). This protonation is crucial for ionization as it transforms the neutral amine into a positively charged ammonium ion. The general form of this reaction is:
Amine + H2O → AmineH+ + OH-
Understanding protonation helps us grasp why certain molecules behave as bases and accept protons when dissolved in water.