Problem 32 - A Complete Resource Book in Chemistry for JEE Main

Question

Mark the correct statement: (a) methylamine is slightly acidic (b) methylamine is less basic than ammonia (c) methylamine is a stronger base than ammonia (d) methylamine forms salts with alkalies

Step-by-Step Solution

Answer

The correct statement is (c) methylamine is a stronger base than ammonia.

Step 1: Understand the Basic Properties of Methylamine

Methylamine (CH₃NH₂) is an organic compound that belongs to a class of amines. It is similar in structure to ammonia ( NH₃), with a methyl group replacing one hydrogen atom. Amines, like methylamine, are generally characterized by their basic properties due to the presence of a lone pair of electrons on the nitrogen atom that can accept a proton.

Step 2: Compare Methylamine and Ammonia Basicity

Methylamine is considered a stronger base than ammonia. The presence of the methyl group ( CH₃) donates electrons to the nitrogen through the inductive effect, making the lone pair on the nitrogen more available to accept protons compared to when it is in ammonia. This electron-donating effect of the methyl group increases the basicity of methylamine compared to ammonia.

Step 3: Identify Basic Reactions with Acids Forming Salts

Methylamine, being a base, can react with acids to form salts, not alkalies. Amines typically form salts when they accept a proton from an acid. Methylamine, being a stronger base, will readily form salts when it encounters strong acids.

Step 4: Evaluate Each Option

(a) Methylamine is slightly acidic - This is incorrect. Amines are basic, not acidic. (b) Methylamine is less basic than ammonia - This is incorrect; methylamine is more basic. (c) Methylamine is a stronger base than ammonia - This is correct due to the electron-donating effect of the methyl group. (d) Methylamine forms salts with alkalies - This is incorrect; it forms salts with acids.

Step 5: Select the Correct Statement

Based on our analysis, the correct statement is (c) methylamine is a stronger base than ammonia, because of the increased availability of the lone pair of electrons for protonation compared to ammonia.

Key Concepts

Methylamine Properties

Methylamine, with the chemical formula CH₃NH₂, is a simple aliphatic amine that is closely related to ammonia (NH₃). It differs by having a methyl group (-CH₃) substitute one hydrogen atom in the ammonia molecule. This slight change in structure introduces crucial differences.

Methylamine is a colorless gas with a fishy, ammoniacal odor. It is highly soluble in water, which makes it a useful intermediary in organic synthesis and industrial applications.

As an amine, methylamine exhibits basic properties due to the lone pair of electrons on the nitrogen atom, which can readily accept a hydrogen ion (proton). This willingness to accept protons is what characterizes it as a base rather than an acid.

Basicity Comparison

Let's dive into why methylamine is a stronger base compared to ammonia. Basicity in chemistry often revolves around the ability of a molecule to donate a pair of electrons and accept protons.

In methylamine, the methyl group (-CH₃) acts through an inductive effect to push electrons toward the nitrogen atom. This increases the electron density around the nitrogen, making its lone pair of electrons more available to engage in protonation.

Conversely, ammonia lacks such an electron-donating group, resulting in less availability of the nitrogen's lone pair for bonding with protons. This makes methylamine a stronger base than ammonia, as its lone pairs more effectively contribute to its basic characteristics.

Amine Reactions with Acids

A key reaction to understand when studying amines is their interaction with acids. Amines are bases, thus they neutralize acids, resulting in the formation of salts.

When methylamine reacts with an acid, it accepts a proton to form a positively charged ammonium ion. The general reaction is:

NH₂CH₃ + H⁺ → NH₃⁺CH₃

This process results in the creation of a compound known as methylammonium salt. It's important to note that amines, including methylamine, do not form salts with bases; this is due to the fact that bases do not donate protons like acids do.

Lone Pair Electron Availability

The availability and behavior of the lone pair electrons on the nitrogen atom in amines like methylamine is central to understanding their chemical properties.

The nitrogen atom in an amine has one lone pair of electrons, which it can use to bond with protons from acids. In methylamine, this lone pair is more reactive due to the electron-donating methyl group next to it. This increases the electron density on the nitrogen, enhancing its capability to attract protons.

This heightened availability of lone pair electrons is what makes methylamine a more potent base compared to simple nitrogen compounds like ammonia. The ability of a molecule to donate its lone pair is fundamental to its role in chemical reactions, especially those involving acids and bases.