Antimony pentachloride is a very acidic substance, and dissolves in water slightly to give a strongly acidic solution consisting mainly of hydrochloric acid (with some dissolved antimony (V)).
Antimony pentachloride is a very acidic substance, and fumes in moist air. It reacts with water vigorously to give a strongly acidic solution consisting mainly of hydrochloric acid (with some dissolved antimony (V)).