On exposure to the atmosphere, a hydrated salt loses its water of crystallization to become anhydrous. This phenomenon is referred to as

Analysis

The question asks for the specific term used to describe the process where a hydrated salt loses its water of crystallization when exposed to the atmosphere, resulting in the salt becoming anhydrous (or forming a lower hydrate).

Concept Explanation

In chemistry, the interaction between salts and atmospheric water vapor (or lack thereof) is categorized into three main phenomena:

1. Efflorescence: This occurs when a hydrated salt has a higher water vapor pressure than the surrounding atmosphere. Consequently, the salt loses its water of crystallization to the air and becomes a powder or anhydrous.
2. Deliquescence: This is the opposite of efflorescence. It occurs when a substance absorbs so much moisture from the atmosphere that it eventually dissolves in the absorbed water to form a solution.
3. Hygroscopy: This refers to substances that absorb moisture from the atmosphere without necessarily dissolving in it. They are often used as drying agents (desiccants).
4. Hydrolysis: This is a chemical reaction where water is used to break down the bonds of a particular substance. It is not related to the physical loss of water of crystallization.

Step-by-Step Solution

• Step 1: Identify the key action in the question: "loses its water of crystallization."
• Step 2: Evaluate the options based on the definitions above.
• Step 3: Since the salt is losing water to the atmosphere, it matches the definition of efflorescence.

Exam Tip

To remember the difference, think of "E" for Efflorescence = Exiting (water is exiting the salt). Think of "D" for Deliquescence = Dissolving (the salt is dissolving into a liquid).