Final answer:
Anhydrous CaCl2 is not used to dry NH3 because it can react with NH3 and form a complex, which traps NH3 and prevents it from being completely dried.
Step-by-step explanation:
Anhydrous CaCl2 is not used to dry NH3 because it can react with NH3 and form a complex, which is a white solid called NH4Cl. This reaction can be represented by the equation:
CaCl2 + 2NH3 → NH4Cl + Ca(NH3)2
This reaction shows that CaCl2 can trap NH3 and prevent it from being completely dried. Therefore, other drying agents like solid KOH or solid NaOH are used instead to dry NH3. These drying agents can react with water and not NH3, allowing NH3 to be completely dried.