In order to determine the rate of photosynthesis (the conversion by plants of carbon dioxide and water into glucose and oxygen), the oxygen gas emitted by an aquatic plant is collected over water at a temperature of 293 K and a total pressure of 754.4 mmHg. Over a specific time-period, a total of 1.20 L of gas is collected. The partial pressure of water at 293 K is 17.55 mmHg. What mass of oxygen gas (in grams) forms?