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

Match each of the following chemical compounds to its characteristic behavior when exposed to moist atmospheric air.

  • Na2CO3⋅10H2O\text{Na}_2\text{CO}_3\cdot 10\text{H}_2\text{O}Loses its water of crystallization to the atmosphere to form a powdery residue.
  • CaCl2\text{CaCl}_2Absorbs water vapor from the atmosphere and dissolves in it to form a solution.
  • CaO\text{CaO}Absorbs moisture from the air without dissolving or forming a solution.

Answer

Na2CO3⋅10H2O\text{Na}_2\text{CO}_3\cdot 10\text{H}_2\text{O} matches with losing water of crystallization to form a powdery residue (efflorescence); CaCl2\text{CaCl}_2 matches with absorbing moisture to form a solution (deliquescence); CaO\text{CaO} matches with absorbing moisture without dissolving (hygroscopy).
Each compound exhibits a specific behavior upon exposure to air: hydrated sodium carbonate loses water of crystallization (efflorescence), calcium chloride absorbs moisture and dissolves (deliquescence), and calcium oxide absorbs moisture without dissolving (hygroscopy).

Step-by-Step Solution

1
Identify the atmospheric phenomenon characteristic of hydrated sodium carbonate (Na2CO3⋅10H2O\text{Na}_2\text{CO}_3\cdot 10\text{H}_2\text{O}).
It undergoes efflorescence, losing water molecules to the surrounding dry air.
Hydrated salts with higher vapor pressure than the atmospheric water vapor pressure tend to lose hydration water.
2
Identify the atmospheric behavior of anhydrous calcium chloride (CaCl2\text{CaCl}_2).
It undergoes deliquescence, absorbing atmospheric moisture until it completely dissolves in the absorbed water.
Deliquescent compounds have an extremely high affinity for water and lower saturated solution vapor pressure than ambient air.
3
Identify the behavior of quicklime (CaO\text{CaO}).
It undergoes hygroscopy, absorbing atmospheric moisture without dissolving into a liquid solution.
Hygroscopic substances absorb moisture into their structure without forming a liquid solution.

Key Concept

Differentiation between efflorescence, deliquescence, and hygroscopy.
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Topics

Water of Crystallization, Deliquescence, Efflorescence, and Hygroscopy

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