A 0.5L vessel is charged with pure calcium oxalate. The vessel is evacuated to remove all substances except CaC204. The tmeperature s increased to 1200 K, so that all CaC204 decomposes to form CaO according to the reactions: The density of the gas mixture at 1200K was 0.70501 g/L. What was the mass of the calcium oxalate initially placed in the vessl? Assume that the volume of CaO in the end is negligible?