The System

A 10-liter expandable container is half-filled with water.  The space above the water is filled with water vapor and any gaseous compounds.  If any gaseous compounds are present, they are assumed to be ideal gases and the total pressure is 1 atm.  The compounds are assumed to exist in only one phase:  solids and gases are not soluble in either mercury or water, and aqueous compounds are neither volatile nor soluble in mercury.