Efflorescence

Efflorescence

Definition

•   The spontaneous dehydration of a compound is called

Efflorescence.

•   The loss of water of crystallization by a hydrated (crystalline substance with water of crystallization )to form anhydrous salts or hydrated with less molecules of water of crystallization is called Efflorescence.

The large no of chemical compound exists in hydrated or anhydrous form. In hydrated form the water molecule attached to the compound are called the water of crystallization. The surrounding atmosphere also has vapours and definite vapour pressure, due to water in atmosphere. If the vapour pressure of the hydrated substance is greater than the surrounding atmosphere, than the hydrated substance loses water molecule to become less hydrous and to make an equilibrium between the hydrated substance and the atmosphere.

Efflorescence, spontaneous loss of water by a hydrated salt, which occurs when the aqueous vapor pressure of materials is greater than the partial pressure of the water vapour in the air. For example, because the vapour pressures of washing soda (Na₂CO₃·10H₂O) normally exceed than that of the water vapour in the these salts effloresce (i.e., lose all or part of their water of hydration), and their surfaces assume a powdery appearance.

In simple words efflorescence is the loss of  water of crystallization from the hydrated  substances into the atmosphere so that an  equilibrium is formed b/w the hydrated  substance and the surrounding atmosphere.

Examples

•                                                                                                                                                                                Examples of Efflorescent substances are;

•                                                                                                                                                                                1. Borax Na2B4O7.H2O (Hydrated substance)

•                                                                                                                                                                                2. Na2SO4.10H2O

•                                                                                                                                                                                3. Na2CO3.10H2O

•                                                                                                                                                                                4. Z4SO4.7H2O and MgSO4.7H2O

•5. Na2CO3.10H2O loses 9 water molecules first and then  becomes completely anhydrous as follows;

•                                                                                                                                                                                Spontaneous

•                                                                                                                                                                                Na2CO3.10H2O ----------------------> Na2CO3 .H2O

•                                                                                                                                                                                Efflorescence /||\

•                                                                                                                                                                                ||

•                                                                                                                                                                                ||

•                                                                                                                                                                                Na2CO3 (Anhydrous)

•                                                                                                                                                                                Since the vapor pressure of the hydrated substance is greater then the atmospheric vapor pressure, so there is a spontaneous loss of water of crystallization till the equilibrium is obtained. After the equilibrium formation no more loss of water molecules occur.

Pharmaceutical Application of Efflorescence

•   Hydrated drug on weight basis is less potent but when it is converted by Efflorescence to its corresponding lower hydrates or anhydrous form than its potency can be increased.

•   Anhydrous form is easy to handle during manufacturing process.

Prevention of Efflorescence

•   Efflorescence or loss of water of crystallization can be prevented by the following ways:

•   By closing the container immediately after use

•   By filling the container completely so that no space for air storage is available above the liquid in the container.

•   By placing a dehydrating agent (silica gel) to absorb water and store in cool place because greater is the temperature, greater is the release of water of crystallization.