Question

Explain why P₂O₅ and CaO cannot be used for drying of hydrogen chloride gas.

Answer 1

Both are basic/reactive compounds that chemically react with the acidic HCl gas to form new salts instead of just drying it.

With CaO:

\[\ce{CaO + 2HCl -> CaCl2 + H2O}\]

With P₂O₅:

\[\ce{P2O5 + 3HCl -> POCl3 + 3HPO3}\]