Which gas, when combined with moisture, forms hydrochloric acid that can burn and blister the mucous membranes of the nose, the linings of the lungs, and the tissue of the mouth and throat?

Which gas, when combined with moisture, forms hydrochloric acid that can burn and blister the mucous membranes of the nose, the linings of the lungs, and the tissue of the mouth and throat?

• A. Chlorine gas
• B. Ammonia
• C. Hydrogen chloride gas
• D. Phosgene

Answer: (C)

The key idea is that some gases become highly corrosive once they meet moisture in the respiratory tract and tissues, because they form acids there. Hydrogen chloride gas dissolves directly in moisture to produce hydrochloric acid, a strong corrosive that can burn and blister the mucous membranes of the nose, lungs, mouth, and throat. That immediate formation of hydrochloric acid in moist tissue explains the characteristic burns and blistering you’d expect from exposure to this gas. Chlorine gas can also lead to similar injury by forming hydrochloric and hypochlorous acids in moisture, but the description centers on the direct formation of hydrochloric acid in moist tissues, which hydrogen chloride gas does most straightforwardly. Ammonia would form ammonium hydroxide, a base, not hydrochloric acid. Phosgene also hydrolyzes to form hydrochloric acid, but its primary hazard is as a choking agent with pulmonary effects, so the direct acid formation described here points to hydrogen chloride gas.

The key idea is that some gases become highly corrosive once they meet moisture in the respiratory tract and tissues, because they form acids there. Hydrogen chloride gas dissolves directly in moisture to produce hydrochloric acid, a strong corrosive that can burn and blister the mucous membranes of the nose, lungs, mouth, and throat. That immediate formation of hydrochloric acid in moist tissue explains the characteristic burns and blistering you’d expect from exposure to this gas.

Chlorine gas can also lead to similar injury by forming hydrochloric and hypochlorous acids in moisture, but the description centers on the direct formation of hydrochloric acid in moist tissues, which hydrogen chloride gas does most straightforwardly. Ammonia would form ammonium hydroxide, a base, not hydrochloric acid. Phosgene also hydrolyzes to form hydrochloric acid, but its primary hazard is as a choking agent with pulmonary effects, so the direct acid formation described here points to hydrogen chloride gas.