Question

There are several arsenic minerals, two of which are claudetite (As2O3) and orpiment (As2S3). Write a balanced half-cell reaction between these two minerals, in an aqueous solution. Assume that the concentration of all aqueous species are equal to 10^-6. Plot the phase boundary between the two minerals on your Eh-pH diagram. And, comment on their stability fields with respect to the oxidation state of HS- and SO4^2-. Not sure to how to go about solving this. Any help would be appreciated.

Data (?Gr°)

As2O3 = -137.66 kCal/mol

As2S3 = -40.30 kCal/mol

SO4^2- = -177.75 kCal/mol

HS- = 2.93 kCal/mol

H20 = -237.129 kJ/mol

Answer 1

and ASa Beth minerals 4 2- En 2 oxidat on State HS and 2-