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Difference Between Double Salt and Complex Salt for JEE Main 2024

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Last updated date: 20th Jun 2024
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What is Double Salt and Complex Salt: Introduction

To differentiate between double salt and complex salt: Double salts are crystalline substances formed by the combination of two different salts through the process of crystallisation. These salts are easily dissociated into their constituent ions when dissolved in water. They possess distinct properties and can exhibit different colours, textures, and solubilities compared to their individual salt components. On the other hand, complex salts are formed when a coordination complex, which consists of a central metal ion surrounded by ligands, combines with one or more simple ions. Complex salts have intricate structures and often exhibit unique chemical and physical properties, such as high stability and catalytic activity. The study of double salt and complex salt plays a crucial role in understanding the behaviour of ions and the formation of various chemical compounds. Read further for more detail.

What is Double Salt?

A double salt in chemistry refers to a crystalline compound formed by the combination of two distinct salts through the process of crystallisation. Unlike a simple mixture of two salts, double salts have a specific stoichiometric ratio between their constituent ions. When dissolved in water, double salts dissociate into their constituent ions, exhibiting different properties compared to the individual salts. These properties include altered solubilities, distinct colours, and unique crystalline structures. Double salts are commonly formed when two salts with similar crystal structures and compatible ion sizes crystallize together, resulting in a compound with enhanced stability and distinctive characteristics. The features of double salt are: 


  • Stoichiometric Ratio: Double salts have a specific stoichiometric ratio between the constituent ions. This ratio remains constant regardless of the conditions, indicating a fixed composition.

  • Unique Properties: Double salts exhibit properties that are different from the individual salts that form them. These properties may include altered solubilities, distinct colors, and unique crystalline structures.

  • Crystal Structure: Double salts often have a distinct crystal structure compared to individual salts. This structure arises from the arrangement of the ions within the crystal lattice, resulting in a unique three-dimensional pattern.

  • Enhanced Stability: Double salts are generally more stable than simple mixtures of salts. The formation of strong ionic bonds between the constituent ions contributes to their increased stability.

  • Specific Formations: Double salts are typically formed when two salts with similar crystal structures and compatible ion sizes crystallize together. The conditions under which they form, such as temperature and concentration, can influence their composition and properties.

  • Dissociation: When dissolved in water, double salts readily dissociate into their constituent ions. This dissociation allows for the ions to be separated and interact with other substances in solution.


What is Complex Salt?

A complex salt, also known as a coordination compound, refers to a chemical compound formed by the combination of a central metal ion with one or more ligands. Ligands are molecules or ions that bond to the metal ion through coordinate covalent bonds. The complex salt possesses a unique structure where the ligands surround the metal ion, forming a coordination sphere. These compounds exhibit distinct chemical and physical properties compared to simple salts. Complex salts play a vital role in various chemical reactions, including catalysis, electron transfer processes, and the coordination of metal ions in biological systems. The features of complex salt are: 


  • Coordination Sphere: Complex salts have a central metal ion that is surrounded by ligands forming a coordination sphere. The ligands bond to the metal ion through coordinate covalent bonds, creating a stable complex.

  • Ligand Exchange: Complex salts often exhibit ligand exchange reactions, where the ligands surrounding the metal ion can be replaced by other ligands. 

  • Color Variation: Complex salts often display vibrant colors due to the presence of transition metal ions in their structures. The absorption and reflection of light by these metal ions result in the observed colors.

  • Stability: Complex salts generally exhibit higher stability compared to simple salts. The coordination bonds between the metal ion and the ligands are typically stronger than the ionic bonds in simple salts.

  • Chemical Reactivity: Complex salts can undergo various chemical reactions due to the presence of the central metal ion. These reactions can involve ligand substitution, redox processes, and coordination isomerism, among others.

  • Catalytic Activity: Many complex salts exhibit catalytic activity, where they can facilitate chemical reactions by providing a favorable environment for the reaction to occur. The metal ion in the complex salt can act as a catalyst, influencing the reaction kinetics.


Differentiate Between Double Salt and Complex Salt

S.No

Category 

Double Salt 

Complex Salt

1.

Composition

Combination of two different salts

Combination of a central metal ion and ligands

2.

Stoichiometry

Fixed stoichiometric ratio between constituent ions

Variable stoichiometry due to ligand exchange

3.

Dissociation

Dissociates into constituent ions when dissolved

Retains its coordination structure in solution

4.

Properties

Altered solubilities, distinct colours, unique structure

Enhanced stability, specific chemical and physical properties

5. 

Crystal Structure

Distinct crystal structure compared to individual salts

Coordination sphere around the central metal ion

6.

Formation

Crystallisation of two salts with compatible structures

Interaction of a metal ion with ligands


These are some of the key difference between double salt and complex salt in the terms of composition, stoichiometry, dissociation, crystal structure, etc.


Summary 

A double salt is a compound formed by the combination of two different salts through the process of crystallisation. It contains two or more distinct cations or anions that are held together in the crystal lattice structure. A complex salt, on the other hand, is a compound formed by the coordination of a central metal ion with one or more ligands. The ligands are typically molecules or ions that have lone pairs of electrons, allowing them to form coordinate bonds with the metal ion. Double salts exhibit altered properties, while complex salts possess enhanced stability and unique chemical characteristics.

FAQs on Difference Between Double Salt and Complex Salt for JEE Main 2024

1. How is a double salt formed?


A double salt is formed through the process of crystallisation when two different salts with similar crystal structures combine. When a solution containing the two salts is evaporated, the ions from both salts come together and arrange themselves in a specific stoichiometric ratio within the crystal lattice. The resulting compound is a crystalline substance with distinct properties. The formation of a double salt requires compatible ion sizes and crystal structures of the constituent salts, allowing for their combination into a single crystalline structure.

2. What are ligands in complex salts?

Ligands in complex salts are molecules or ions that bind to a central metal ion through coordinate covalent bonds. They surround the metal ion, forming a coordination complex or coordination sphere. Ligands typically possess one or more lone pairs of electrons that they donate to the metal ion, forming a stable coordination bond. The nature of the ligands determines the properties and reactivity of the complex salt. Ligands can be simple molecules like water or ammonia, or more complex molecules with multiple donor atoms, such as ethylenediamine or cyanide ions.

3. What properties make double salts unique?

Double salts possess several unique properties that set them apart from simple mixtures of salts. One of their distinctive features is their specific stoichiometric ratio, where the constituent ions combine in fixed proportions within the crystal lattice. This results in a compound with distinct physical and chemical properties, including altered solubilities, unique colors, and different crystalline structures compared to individual salts. Furthermore, double salts readily dissociate into their constituent ions when dissolved in water, exhibiting behavior different from simple mixtures.

4. Do complex salts have specific stoichiometric ratios?

Complex salts do not have specific stoichiometric ratios like double salts. The composition of a complex salt can vary depending on the metal ion and ligands involved. The coordination number of the metal ion and the number and type of ligands determine the overall stoichiometry of the complex. Ligand exchange reactions can further alter the composition of a complex salt, allowing for the substitution of one or more ligands.

5. Can a double salt dissociate into its constituent ions?

Yes, a double salt can dissociate into its constituent ions when dissolved in water or another suitable solvent. Double salts, like other ionic compounds, are held together by ionic bonds between the positive and negative ions. When placed in a solvent, the solvent molecules surround the ions and disrupt the ionic bonds, causing the double salt to dissociate into its component ions. This dissociation allows the ions to move freely in the solution and enables various chemical and physical processes involving the individual ions.