Distinguish between efflorescent and hygroscopic substances.
Here is an article on hygroscopy.
http://en.wikipedia.org/wiki/Hygroscopy
Here is an article on efflorescence.
http://en.wikipedia.org/wiki/Efflorescence
Efflorescent and hygroscopic substances are both related to the ability of a substance to interact with moisture and change its physical properties. However, they have different characteristics:
1. Efflorescent substances: These substances tend to lose moisture when exposed to air, leading to the formation of powdery deposits on the surface. The process is called efflorescence. It occurs when a hydrated substance, such as a salt, has more water molecules in its crystal lattice than it can maintain when exposed to lower humidity. As a result, the excess water evaporates, leaving behind a white or grayish powder on the surface.
To identify if a substance is efflorescent:
- Take a sample of the substance.
- Place it in a dry environment with low humidity.
- Observe if any powdery deposits form on the surface over time.
2. Hygroscopic substances: These substances have a high affinity for moisture and tend to absorb it from the surrounding environment. They can attract and hold water molecules, even in humid conditions. This property is useful in applications where it is necessary to keep a substance dry or to maintain a certain level of moisture in a system.
To identify if a substance is hygroscopic:
- Take a sample of the substance.
- Expose it to a humid environment or add a small amount of water vapor to the sample.
- Observe if the substance absorbs or retains moisture, causing it to become damp or even dissolve.
In summary, efflorescent substances lose moisture and form powdery deposits in a dry environment, while hygroscopic substances attract and absorb moisture from the surrounding environment.