Hygroscopicity and Moisture Interactions

Study Notes

Hygroscopicity

The ability of a substance to attract and hold water molecules from the surrounding environment.
The degree to which a substance is hygroscopic is called hygroscopicity.
Hygroscopicity is important in many applications, especially those involving moisture.
Examples:
- Mixing a primary amine with lactose keeps the primary amine stable even when stored at 90°C for 12 weeks.
- Deliquescence and efflorescence, which occur when the solid dissolves and saturates a thin film of water on its surface or when the crystal loses water of crystallization.
Deliquescence is where a solid dissolves and saturates a thin film of water on its surface.
- This process is dictated by temperature and relative humidity.
Efflorescence is the opposite of deliquescence, which occurs when the crystal loses water of crystallization below a critical water vapor pressure.
- Caffeine hydrate lost its water of crystallization even at 61% RH.

Relative Humidity (RH)

The ratio of the partial pressure of water vapor (ew) to the equilibrium vapor pressure of water (ew*) at the same temperature.
Normally expressed as a percentage.
Depends on the temperature and the system of interest.

Vapor Pressure

The pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system.
Can be calculated using the Antoine equation or the August equation.
- Antoine equation: 𝐥𝐨𝐠𝟏𝟎 𝐩 = 𝐀 − 𝐁 / (𝐂 + 𝐓)
- August equation: 𝐥𝐨𝐠𝟏𝟎 𝐩 = 𝐀 − 𝐁 / 𝐓

Hygroscopicity Classification

Hygroscopicity is an important parameter in solid state properties.
Moisture sorption isotherm is a graph that shows the relationship between the moisture content of a substance and the relative humidity of the surrounding environment.

Lipophilicity

Partition Coefficient : Ratio of the concentration of the compound in the two phases of a mixture of two immiscible solvents at equilibrium.
- Octanol-water partition coefficient: Drug conc.in octanol / Drug conc.in water
  - Log P
  - =0 equal amount
  - 0 more lipid soluble

Description

Explore the concept of hygroscopicity, the ability of substances to attract and hold water molecules. This quiz covers critical processes such as deliquescence and efflorescence, and their importance in various applications related to moisture. Test your understanding of how these processes operate under different temperature and humidity conditions.

Hygroscopicity and Moisture Interactions

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Questions and Answers

What property describes the ability of a substance to attract and retain water?

Which term is used to describe a solid that dissolves in a thin film of water on its surface?

What happens during efflorescence?

Relative humidity (RH) is defined as which of the following?

What is the main determining factor for relative humidity?

Which equation relates vapor pressure to temperature?

What is the log P in lipophilicity related to?

What can significantly affect the storage and stability of materials?

Which process describes the adsorption of moisture leading to a solution formation?

What is hygroscopicity the measure of?