We have seen that arsenic can exist in many different chemical species. Suppose the only method you have available at your lab for determining arsenic content is the colorimetric method seen in the previous problem: AsO2- + Red-K9 ---> AsO2-Red-K9-.
Unfortunately, your samples also contain arsenate besides the arsenite that can be quantified with this analytical method.
Luckily enough you have L-cysteine available, a compound that can reduce the arsenate to arsenite according to the following reaction: AsO4-3 + 2 L-cysteine ---> AsO2- + L-cystine.
What is the concentration of arsenic (in mg/L) in this sample? (please, give your answer with three significant figures.)