Question

Explain the important distinctions between each pair of terms: (a) acid salt and acid anhydride; (b) azide and nitride; (c) white phosphorus and red phosphorus; (d) ionic hydride and metallic hydride.

Short answer

Acid salts are formed by partially replacing the replaceable hydrogen atoms of an acid molecule, while Acid anhydrides are dehydrated acids. Azides contain the group -N3 and Nitrides are compounds of nitrogen with less electronegative elements. White phosphorus is a reactive solid and red phosphorus is a non-toxic solid used where a controlled ignition is required. Ionic hydrides have hydrogen bonded with a more electropositive element so it has a charge of -1, while Metallic hydrides are formed with transition metals where hydrogen present doesn't have charge of -1.

Step-by-step solution

Understand Acid Salt vs Acid Anhydride

An acid salt is a type of salt which is formed by partial replacement of replaceable hydrogen atoms of an acid molecule. On the other hand, Acid anhydrides are compounds that provide an acid when combined with water. They are technically 'dehydrated acids' and can convert back into acids by absorbing water. Acid Anhydrides are generally formed by removing water from an acid.

Understand Azide vs Nitride

Azides are compound containing the group -N3 or individual ions carrying a charge of -1/3. In terms of resonance, azides can be described as a resonance hybrid of two structures. Nitrides on the other hand, are binary compounds of nitrogen with less electronegative elements – elements from the first three groups of the periodic table. For example: Sodium Nitride (Na3N) , Aluminum Nitride (AlN).

Understand White Phosphorus vs Red Phosphorus

White phosphorus and red phosphorus are different forms of phosphorus, known as allotropes. White phosphorus is a waxy, highly reactive solid that is typically stored in water to prevent it from spontaneously combusting in the air. Red phosphorus, on the other hand, is an amorphous non-toxic solid that is used in matches, pyrotechnics, and other applications where a controlled ignition is required.

Understand Ionic Hydride vs Metallic Hydride

Ionic hydrides are compounds in which hydrogen is bonded with a more electropositive element so that it exhibits a charge of -1. Metallic hydrides are formed with transition metals. In these types of hydrides, the hydrogen is present in 'interstitial sites' in the metal lattice and does not have a charge of -1. Instead, they feature delocalised electrons (like metallic bonding).

Key concepts

Acid Salt

Acid salts are interesting compounds in chemistry that form from the partial replacement of hydrogen atoms in an acid by metals. This means that not all the replaceable hydrogen ions in the acid are substituted by metal ions. As a result, acid salts retain some of their acidic properties, hence their name. A classic example is sodium bisulfate ( \( \text{NaHSO}_4 \) ). Here, one of the hydrogen ions in sulfuric acid ( \( \text{H}_2\text{SO}_4 \) ) is replaced by a sodium ion.
Acid salts are important in various fields, such as buffer solutions in laboratories, where they help maintain a constant pH. It’s crucial to differentiate them from acid anhydrides, which are formed by removing water from acids. While acid salts can sometimes release hydrogen ions, acid anhydrides can form acids when they absorb water.
Key Characteristics:

• Formed by partial replacement of hydrogen in acids.
• Can sometimes release hydrogen ions.
• Often used in buffering solutions in chemistry.

Azide

Azides are a fascinating group of compounds that contain a linear arrangement of three nitrogen atoms, forming a functional group known as -N3. They are well-known for being potentially explosive due to their ability to quickly release nitrogen gas when decomposed. The azide ion carries a charge of -1, and these compounds are typically resonance-stabilized, meaning they can exist in different forms that contribute to their overall stability.
Azides are significant in various scientific applications, including pharmaceuticals, the synthesis of other chemicals, and propellants in airbag systems. However, it’s vital to handle them with care because of their explosive nature.
Key Characteristics:

• Contain the -N3 group.
• Resonance-stabilized structures.
• Used in pharmaceuticals and airbag systems.
• Potentially explosive.

Allotropes of Phosphorus

Phosphorus exhibits several allotropes, among which white phosphorus and red phosphorus are the most commonly discussed. These allotropes reflect different structural forms of the same element. White phosphorus is known for being highly reactive and is typically stored underwater to prevent it from igniting spontaneously in air.
In contrast, red phosphorus is much more stable and doesn't ignite easily. It is widely used in matchsticks and pyrotechnics, where controlled ignition is beneficial. The difference between these allotropes arises from their atomic structures: white phosphorus consists of P4 tetrahedra, whereas red phosphorus is more polymeric in nature. Because of these structural differences, white phosphorus is toxic, while red phosphorus is considered less harmful.
Key Characteristics of White Phosphorus:

• Highly reactive.
• Composed of P4 tetrahedra.
• Must be stored underwater.

Key Characteristics of Red Phosphorus:

• Amorphous and stable.
• Used in matches and pyrotechnics.

Understanding these forms helps in appreciating the diverse applications and reactive properties of phosphorus.

Ionic Hydride

Ionic hydrides are compounds formed when hydrogen is bonded with more electropositive elements, typically from Group 1 and Group 2 of the periodic table, such as alkali and alkaline earth metals. In these compounds, hydrogen gains an electron to form a hydride ion with a charge of -1. For example, sodium hydride ( \( \text{NaH} \) ) is an ionic hydride.
These hydrides are significant as reducing agents in chemical reactions and are often used in industrial processes to synthesize other compounds. They differ from metallic hydrides, where hydrogen is absorbed into the metal lattice. In metallic hydrides, like those formed with transition metals, hydrogen does not have a fixed charge, and there is involvement of delocalized electrons leading to metallic bonding characteristics.
Key Characteristics:

• Formed with more electropositive elements.
• Hydrogen gains an electron, forming a hydride ion (-1 charge).
• Used as reducing agents in industry.

Understanding ionic hydrides aids in grasping their utilization in synthesis reactions in the field of chemistry.