What Is Deliquescence?

Deliquescence, the process by which a substance absorbs moisture from the atmosphere until it dissolves in the absorbed water and forms a solution. Deliquescence occurs when the vapour pressure of the solution that is formed is less than the partial pressure of water vapour in the air. 

Unlike hygroscopy, however, deliquescence involves absorbing sufficient water to form an aqueous solution. Most deliquescent materials are salts, including calcium chloride, magnesium chloride, zinc chloride, ferric chloride, carnallite, potassium carbonate, potassium phosphate, ferric ammonium citrate, ammonium nitrate, potassium hydroxide, and sodium hydroxide. 

What You Need To Know About Deliquescence

• Deliquescent substances are solids that absorb moisture from the atmosphere until they dissolve in the absorbed water and form solutions.
• Deliquescent substances are called desiccants.
• Deliquescent substances can absorb a high amount of water vapor.
• Deliquescent substances have a very high affinity for water.
• Deliquescent substances form an aqueous solution by absorbing water vapor.

What Is Efflorescence?

Efflorescent substances are solids that can undergo spontaneous loss of water from hydrated salts. Hydrated salts are inorganic salts containing water molecules combined in a definite ratio. These salts can lose these water molecules when kept outside. This process is known as efflorescence.

Efflorescence occurs when the aqueous vapor pressure of the hydrate is greater than the partial pressure of the water vapor in the air. Efflorescent substances include most hydrated salts. Examples include Na₂SO₄, 10H₂O, Na₂CO_3, 10H₂O, and FeSO₄.  A common example of efflorescence is drying of cement.

However, when these water molecules are lost from the hydrated salt, the salt shows a powdery surface due to the loss of water. Eventually, the salt crystals will remain in the container. The phase of water is changed to the gaseous phase.

What You Need To Know About Efflorescence

• Efflorescent substances are solids that can undergo spontaneous loss of water from hydrated salts.
• Efflorescent substances are crystals.
• Efflorescent substances do not absorb water vapor.
• Efflorescent substances have no considerable affinity for water.
• Efflorescent substances do not form a solution.

What Is Hygroscopic?

Hygroscopy is the phenomenon of attracting and holding water molecules via either absorption or adsorption from the surrounding environment, which is usually at normal or room temperature. If water molecules become suspended among the substance’s molecules, adsorbing substances can become physically changed, e.g., changing in volume, boiling point, viscosity or some other physical characteristic or property of the substance.

Hygroscopic substances include cellulose fibers (such as cotton and paper), sugar, caramel, honey, glycerol, ethanol, wood, methanol, sulfuric acid, many fertilizer chemicals, many salts (like calcium chloride, bases like sodium hydroxide etc.), and a wide variety of other substances.

What You Need To Know About Hygroscopic

• Hygroscopic substances are solids that can absorb or adsorb water from its surroundings.
• Hygroscopic substances are called humectants.
• Hygroscopic substances can either absorb or adsorb water vapor.
• Hygroscopic substances have a less affinity for water.
• Hygroscopic substances do not form a solution, but absorb water vapor.

Also Read: Difference Between Imbibition And Diffusion

Efflorescence Vs Deliquescence Vs Hygroscopic Substances In Tabular Form