[dolphinsea14]

I need help with the reasoning of the last part in Preparatory problem 28
Depending on the reaction conditions, the product can be either compound A or
compound B, both of which contain only gold, selenium, and oxygen. Two different
200 mg samples of finely powdered metallic gold were mixed with 350 mg of pure
selenic acid and heated in an autoclave under different conditions, leading to the
production of either 401.4 mg of A or 337.0 mg of B (assuming 100% yield). After
filtering the precipitated A or B, the remaining solution was poured into an
aqueous solution containing excess KI. In both cases (A or B), 20.3 mL of 0.10 M
Na2S2O3
 solution was needed to titrate the released iodine.
(n) Identify compounds A and B, and write balanced chemical equations for their
production.
This is the solution given A: Au2(SeO32(SeO4)
 2 Au + 4 H2SeO4 → Au2(SeO3)2(SeO4) + H2SeO3 + 3H2O
B: Au2(SeO3)2O
2 Au + 3 H2SeO4 → Au2(SeO3)2O + H2SeO3 + 2H2O. No more data. how did they determine the formulas of A and B?

[Borek]

I would start finding out what reacts with iodide.

Even without this information you know how much gold is in each sample, and you now the rest is a mixture of Se/O, that's already enough to predict some possible empirical formulas. Stoichiometric information from the reaction with iodide will narrow these down.