Estimate the molar volume of Isobutylene at 230  C and 32 bar.  Compare your estimate to what you would obtain with the ideal gas law

The Pitzer method is a common methodology used to improve the accuracy of PVT data estimates obtained from the compressibility chart.  In this method, an acentric factor , ω, is defined as:

is the reduced saturation pressure at a temperature that is 70% of the critical temperature.  The compressibility is then 

are functions of temperature and pressure but are the same for all substances (but ω varies from substance to substance).  Values for ω, Z0 and Z1 are tabulated in Lee-Kesler tables.