The binary system nitroethane/decahydronaphthalene (DEC) shows partial miscibility, with the two-phase region lying between x=0.08 and x=0.84, where x is the mole fraction of nitroethane. The binary system liquid carbon dioxide/DEC is also partially miscible, with its two-phase region lying between y=0.36 and y=0.80, where y is the mole fraction of DEC. Nitroethane and liquid carbon dioxide are miscible in all proportions. The addition of liquid carbon dioxide to mixtures of nitroethane and DEC increases the range of miscibility, and the plait point is reached when z, the mole fraction of CO₂, is 0.18 and x=0.53. The addition of nitroethane to mixtures of carbon dioxide and DEC also results in another plait point at x=0.08 and y=0.52.

(a) Sketch the phase diagram for the ternary system,

(b) For some binary mixtures of nitroethane and liquid carbon dioxide the addition of arbitrary amounts of DEC will not cause phase separation. Find the range of concentration for such binary mixtures.