Difference Between Double Salt and Complex Salt

Main Difference – Double Salt vs Complex Salt

In chemistry, a salt is an ionic compound composed of a cation and an anion. A cation is a positively charged chemical species, and an anion is a negatively charged chemical species. Therefore, a salt is a neutral compound. When cations and anions interact with each other, they are combined in such a way that the overall charge of the salt becomes zero. The cations and anions bond together through ionic bonds. Double salts and complex salts are two types of salts that are found in chemistry. The main difference between double salt and complex salt is that a double salt is a combination of two salt compounds whereas a complex salt is a molecular structure that is composed of one or more complex ions.

Key Areas Covered

1. What is a Double Salt
      – Definition, Properties, and Examples
2. What is a Complex Salt
      – Definition, Properties, and Examples
3. What is the Difference Between Double Salt and Complex Salt
      – Comparison of Key Differences

Key Terms: Anion, Cation, Complex Salt, Double Salt, Ionic Compound, Salt

What is a Double Salt

A double salt is a compound prepared by a combination of two different salt compounds. Therefore, a double salt is composed of more than one anion and cation. A double salt is prepared by dissolving the salt compounds in the same liquid followed by crystallization in a regular pattern.

Figure 1: Ammonium Iron (ll) Sulfate is a Double Salt

When dissolved in water, a double salt is dissociated completely into all the ions. An aqueous solution of a double salt is composed of cations and anions which were in the initial two salt compounds. Therefore, this dissociation produces simple ions in the aqueous solution.

A double salt can easily be analyzed by dissolving it in water due to its complete dissociation in water. However, when preparing a double salt, the components (two salts) should be mixed in an equimolar ratio. In other words, the same amount of moles should be mixed. Otherwise a uniform, regular lattice cannot be obtained.

Some examples of double salts are alums, Tutton’s salt, potassium sodium tartrate, bromlite, etc. The properties of the double salt crystals are different from the properties of the initial salts used in the preparation of the double salt.

What is a Complex Salt

A complex salt is a compound composed of a central metal atom having coordination bonds with ligands around it. This also called a coordination compound. This compound is called a complex salt because the structure is complex and there are cations and anions bonded to each other.

Figure 2: Dimethylglyoxime is a Complex Salt

A complex salt is not completely dissociated into its ions when added to water. Instead, they remain as complex structures. This complex formation is helpful in the chelation of metal ions. Here, the metal ions are bonded to chemical species called ligands through coordination bonds, resulting in the metal ion unavailable for any other chemical reaction that takes place in a reaction mixture. This is important in chemical reactions where interferences coming from certain metal ions should be removed.

However, a complex salt cannot be analyzed by dissolving it in water since complex salt does not give simple ions. A complex salt is prepared by mixing two different salts in a stoichiometric ratio. Then the correct amount of ligands will bind with the metal ion.

Difference Between Double Salt and Complex Salt

Definition

Double Salt: A double salt is a compound prepared by the combination of two different salt compounds.

Complex Salt: A complex salt is a compound composed of a central metal atom having coordination bonds with ligands around it.

Dissociation

Double Salt: Double salts completely dissociate into its ions in water.

Complex Salt: Complex salts do not completely dissociate into its ions in water.

Resulting Ions

Double Salt: Double salts give simple ions when added to water.

Complex Salt: Complex salts do not give simple ions.

Analysis

Double Salt: Double salts can easily be analyzed by determining the ions present in the aqueous solution.

Complex Salt: Complex salts cannot be easily analyzed by determining the ions in the aqueous solution.

Conclusion

A salt is essentially composed of an anion and a cation. Therefore, double salts and complex salts also contain cations and anions. Although both of them are called salts, they differ from each other according to their preparation method and the chemical behavior. But the main difference between a double salt and a complex salt is that a double salt is a combination of two salt compounds whereas a complex salt is a molecular structure that is composed of one or more complex ions.

References:

1. “Double salt and complex salt.” Chemical Forums, Available here. Accessed 5 Sept. 2017.
2. “Double salt.” Wikipedia, Wikimedia Foundation, 26 Aug. 2017, Available here. Accessed 5 Sept. 2017.

Image Courtesy:

1. “Mohr’s salt 02” By Giulio1996Cordignano – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “Dimethylglyoxime” By Klaus Hoffmeier – Own work (Public Domain) via Commons Wikimedia