402 DIY Science: Illustrated Guide to Home Chemistry Experiments
RQEWEvI UESTIOnS
q 1 : The mean lethal dose of arsenic in humans is variously estimated at between 1 mg/kg (0.001 g per 1,000 g) and 3 mg/kg.
You know that the Marsh Test can detect arsenic in amounts as small as 1 μg (0.000001 g). A murder has taken place, and arsenic
poisoning is suspected. You are tasked with using the Marsh Test to determine whether arsenic was the murder weapon. The victim
weighed 100 kg, and you have only a 10 g sample of the victim’s stomach contents to work with. If arsenic was used to kill this victim,
is the Marsh Test sensitive enough to detect the arsenic? If so, and assuming that the victim died from a dose of only 1 mg/kg, how
much smaller could your sample be and still yield usable results? If not, how much larger a sample would you require?
q: 2 Regulations restricting the use of CCA are becoming more common because of concerns that the CCA may leach out of the
treated wood and into the surrounding soil. Tests have detected arsenic levels as high as 14 ppm in soil that is in contact with CCA-
treated landscape timbers. If the Marsh Test can detect arsenic in amounts as small as 1 μg, how large a soil sample would you need to
use the Marsh Test successfully?