1. The problem statement, all variables and given/known data A tank contains 25.0 kg of O2 gas at a gauge pressure of 9.10 atm. If the oxygen is replaced by fluorine, how many kilograms of the latter will be needed to produce a gauge pressure of 4.00 atm? 2. Relevant equations PV=nRT 3. The attempt at a solution For the O2 we know P, can find n (m=nM), and R is a constant. Still leaves one equation with two unknowns? Am I to assume some temperature, find the volume of the container, and then use that same temperature to calculate the mass of flourine. Is that valid?