Chapter 11, Problem 11.7P

For the purpose of estimating hazards from toxic vapors or gases of high molecular weight, it is sometimes incorrectly assumed that settling of the vapor is determined by the specific gravity of the pure vapor, which is defined as

Molecular weight of the pure vapor
"Molecular weight" of air

instead of the correct specific gravity given by

" Molecular weight" of air and vapor mixture
"Molecular weight" of air

(a) If the vapor pressure of benzene (benzol), ${\text{C}}_{\text{6}}{\text{H}}_{\text{6}}$ , is 160 mm Hg at 20ºC, calculate the correct specific gravity of a saturated air mixture of benzene vapors and compare it to the specific gravity of the pure vapor.
(b) If the chemical PEL for benzene is 10 ppm by volume, calculate the specific gravity of an air—benzene mixture of this concentration.
(c) What is the maximum specific activity of ${}^{\text{14}}\text{C}$ -tagged benzene in order that one-half the radiological DAC for ${}^{\text{14}}\text{C}$ ( $\text{DAC = 1}\times {\text{10}}^{\text{-6}}{\text{µCi/cm}}^{\text{3}}$ ) not be exceeded by a benzene concentration of 10 ppm?