1. The problem statement, all variables and given/known data I was asked to find the vapour pressure and saturated liquid molar density of propane at 263.15K using a generalised compressibility chart. (not allowed to use NIST or steam tables either, the chart i was given does not have reduced volume lines) 2. Relevant equations Tr=T/Tc Pr=P/Pc z=Pv/nRT 3. The attempt at a solution The reduced temperature is 0.712. I calculated the critical point compressibility to be 0.276 but that probably has nothing to do with what i was asked to find. Compressibility is a function of reduced temperature and pressure....... Tried using the chart with reduced temperature line at 0.7, followed the line to where it meets the line ends, got a reduced pressure of about 0.1, compressibility of about 0.88. But using the z=Pv/nRT equation above i got a density of 198 mol m^3 which is the saturated vapour density, not the saturated liquid density i was asked to find. I was also told that "you look at the figure for the compressibility factor Z=Pv/(RT) as a function of P/Pc you will find that it is a unique universal curve where Z is not need to given in reduced units" which i do not understand sadly.