50 points! A slurry of barium sulfate is ingested just before an X-ray of the gastrointestinal tract is taken because the precipitate is opaque to x-rays and thus defines the contours of the tract. The Ba- ion is toxic, but the compound is nearly insoluble. If 4Gº at 37°C (body temperature) is 59.1 kJ/mol for the process

BaSO4(s) = Ba²+(aq) + SO4²- (ag)

what is [Ba²+] in mol/L in the intestinal tract? Assume the only source of sulfate ions is the ingested slurry.