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# Ammonium Ion- [NH4]+

## What is Ammonium Ion?

“Ammonium is a polyatomic cation with a chemical formula

$$\begin{array}{l}NH_{4}^{+}\end{array}$$
.

A cation is an electron-deficient species that carries a positive charge. A polyatomic ion, also known as a molecular ion, is a covalently bonded set of two or more atoms or a metal complex that can be thought of as a single unit and has a net charge that is greater than zero.

In the case of ammonium, four hydrogen atoms are bonded to one central nitrogen atom, with a total charge of +1.

## Formation of Ammonium Ion

“When a neutral ammonia compound NH3 is protonated or takes on an additional positively charged hydrogen atom, an ammonium ion is formed.”

NH3 + H+

$$\begin{array}{l}NH_{4}^{+}\end{array}$$

In ammonia, nitrogen is a central atom with 5 electrons in its valence shell, 3 of which are shared with 3-H atoms, and 1 lone pair of electrons complete the valence shell configuration.

It is an electron-rich species (nucleophile) because it has one lone pair electron (unshared electron pair) and can donate this electron pair to another atom (electrophile). As a result, ammonia is a donor, and when the Ammonia atom donates its lone pair to the proton ammonium ion is formed.

## Structure and Bonding

Being polar covalent bonds, all four N–H bonds are equivalent. The ion is isoelectronic with methane and borohydride and has a tetrahedral structure.

## Properties of Ammonium Ion

Name of Molecule

Ammonium ion

Chemical formula

[NH4]+

Molar mass

18.039 g/mol

Conjugate base

Ammonia(NH3)

Nature

Weak acid

Acidity (pKa)

9.25

1. Ammonium salts are all white and soluble in water.

2. Chemically, the ammonium ion behaves similarly to the ions of alkali metals, particularly the potassium ion, which is nearly the same size.

3. Since it degrades in water to form ammonia and a hydrogen ion, the ammonium ion acts as a weak acid in aqueous solutions.

[NH4]+(aq) ⇋ NH3(aq) + H+(aq)

## Ammonium Salts

• Ammonium salts are ionic compounds with the formula (R)4N+A, where R represents hydrogen, alkyl, or aryl group and A represents an anion.
• When R is alkyl or aryl, the salts are known as quaternary ammonium salts. The quaternary ammonium cations are permanently charged, regardless of solution pH. The majority of ammonium salts are water-soluble and strongly dissociated. Cleaning agents, food additives, diuretics, surfactants, antistatic agents, and disinfectants are all made from ammonium salts. They have been shown to have antimicrobial properties. Quaternary ammonium salts maintain cellular osmotic pressure.
• Quaternary ammonium compounds with long alkyl chains, such as benzalkonium chloride, cetylpyridinium chloride, dofanium chloride, benzethonium chloride, methyl benzethonium chloride, cetalkonium chloride, and didecyldimethylammonium chloride, have antibacterial, fungicidal, and antiviral activity. Since anionic detergents deactivate these quaternary ammonium compounds, they should not be used in hard water. They are commonly used as sanitizers. One of the most common applications of quaternary ammonium salts in organic synthesis is as phase transfer catalysts (PTCs), which catalyse the reaction between ionic and organic reactants. Chlormequat chloride acts as a plant growth regulator by inhibiting gibberellin production.

## Applications

• Ammonium ions are a byproduct of animal metabolism. It is excreted directly into the water by fish and aquatic invertebrates. It is converted to urea in mammals, sharks, and amphibians during the urea cycle because urea is less toxic and can be stored more efficiently.
• Metabolic ammonium is converted into uric acid in birds, reptiles, and terrestrial snails, which is solid and can thus be excreted with minimal water loss.
• Ammonium is an important nitrogen source for many plant species, particularly those that grow in hypoxic soils. However, it is toxic to the majority of crop species and is rarely used as the sole nitrogen source.
• The ammonium ion [NH4]+ in the body is essential for maintaining acid-base balance.

## How to Detect Ammonium Ion?

Ammonium ions in a solution can be identified by adding a dilute sodium hydroxide solution and gently heating it. Ammonium ions will be converted to ammonia gas if they are present. Ammonia has a distinct choking odour. It also blues damp red litmus paper and damp universal indicator paper.

## Frequently Asked Questions on Ammonium Ion- [NH4]+

### Why is ammonium an ion?

When an ammonia molecule, NH3, reacts with a proton, H+ cation, the unshared or lone pair of electrons in the N-atom form a coordinate or dative bond with the H+, forming an ion, which is known as ammonium ion.

### What is the formal charge on ammonium ion?

The formal charge on ammonium ion is +1.

### Which test is a confirmatory test for ammonium ion?

If the solution releases a gas with a characteristic smell when an alkali hydroxide is added to it and heated, it will confirm the presence of ammonium ions. Ammonium ions on reaction with alkali hydroxide form ammonia gas.

### Where are ammonium ions found?

Dilute ammonia solution and any ammonium salt, such as ammonium chloride, contain ammonium ions.

### Is ammonium ion acidic or basic?

An acid is something that when dissolved in an aqueous solution, produces protons. When ammonium ion is dissolved in an aqueous solution, it splits into two ions NH3 and H+. Therefore, the ammonium ion is a weak acid.