Question

Difficulty: MediumWater of Crystallization, Deliquescence, Efflorescence, and Hygroscopy

Match each hydration phenomenon or property on the left with its corresponding vapor pressure behavior or physical description on the right.

  • DeliquescenceOccurs when the saturated solution's vapor pressure is lower than ambient water vapor pressure, leading to absorption of water until the solid dissolves into a solution.
  • EfflorescenceOccurs when the hydrated crystal's vapor pressure exceeds ambient water vapor pressure, resulting in the loss of hydration water to form a powdery residue.
  • HygroscopyThe absorption of atmospheric moisture by a substance without liquefying or forming a solution.
  • Water of CrystallizationDefinite stoichiometric quantity of water molecules chemically bound within the solid crystal lattice of a salt.

Answer

Deliquescence matches with the condition where the saturated solution's vapor pressure is lower than ambient water vapor pressure, causing complete dissolution; Efflorescence matches with the condition where the crystal's vapor pressure exceeds ambient water vapor pressure, causing loss of hydration water; Hygroscopy matches with the absorption of moisture without dissolving; Water of Crystallization matches with the definite stoichiometric water molecules bound in the crystal lattice.
Each phenomenon is correctly paired based on its vapor pressure relationship and physical characteristics: Deliquescence requires the vapor pressure of the saturated solution to be lower than ambient water vapor pressure, causing liquefaction. Efflorescence requires the crystal's vapor pressure to exceed ambient water vapor pressure, leading to water loss. Hygroscopy involves moisture absorption without dissolving, and water of crystallization represents the fixed stoichiometric water bound in the crystal lattice.

Step-by-Step Solution

1
Analyze the thermodynamic driving force for deliquescence.
A substance deliquesces when it absorbs water from the air until it dissolves. This occurs because the saturated solution formed has a vapor pressure lower than the partial pressure of water vapor in the atmosphere.
Water spontaneously condenses into a system with lower vapor pressure.
2
Analyze the thermodynamic driving force for efflorescence.
A hydrated salt effloresces when its internal hydration vapor pressure is greater than the atmospheric water vapor pressure, causing water molecules to escape into the atmosphere.
Water leaves the crystal lattice when the internal vapor pressure is higher than ambient humidity.
3
Distinguish hygroscopy from deliquescence.
Hygroscopic substances absorb moisture from the atmosphere, but unlike deliquescent substances, they do not dissolve to form liquid solutions.
Hygroscopic materials absorb moisture into their bulk or surface without forming a solution.
4
Define water of crystallization.
Water of crystallization refers to water molecules chemically trapped in a fixed mole ratio inside the crystal lattice of salts.
It determines the specific hydrated chemical formula of the salt.

Key Concept

Atmospheric behavior of hydrated and anhydrous salts based on vapor pressure relationships.
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