1. The problem statement, all variables and given/known data I need to find the volume for 1 kg of diatomic oxygen for a pressure of 150,000 Pa and a temperature of 100K. This is really part of a larger project, and I need to make sure I'm not tripping up on little details. It's that 1 kg of diatomic oxygen that I am a bit unsure about, or just plain having a brain freeze about. R* = 8.314 J/K*mol T = 100 K P = 150,000 Pa n = ?? 2. Relevant equations PV = nRT 3. The attempt at a solution Solving the equation for V; V = nRT/P. No big deal. My problem is making sure I have the correct n in the equation. The mass of diatomic oxygen is 32.0 grams, which is what I was using in my solutions. However, I realize that I have 1 kg of O2, not 1 g of it. Should I really be using 32,000 for my n? Or something else?