The compound semiconductor family Indium-Phosphide-Arsenide InPxAS1-x has the zinc blende crystal structure: FCC with In at 0,0,0 and P/As at 1/4, 1/4, 1/4. The lattice parameter a follows Vegard's Law (Rule of Mixtures), that is, a = amp(X) + aInAs(1-X). An X-ray diffraction measurement (using Cu-Ka, 2 = 1.54A) is performed on an unknown sample of InPxAS1-x. If the first allowed X-ray reflection occurs at an angle of 12.810, calculate the mass density of the unknown sample. Problem data: dimp = 5.8687 A; dinAs = 6.0583 A; Atomic masses (in amu): In = 114.8; P = 30.97; As = 74.92