an acid compound found in plants and vegetables such as rhubarb, has a mass percent composition of 26.7% c, 2.24% h, and 71.1% o. it can interfere with respiration and cause kidney or bladder stones. if a large quantity of rhubarb leaves is ingested, this acid can be toxic. the lethal dose (ld50) in rats for this acid is 375 mg/kg. rhubarb leaves contain about 0.5% by mass of the acid. what is the empirical formula of the acid?