[Rutherford]

The aqueous solution of a salt underwent hydrolysis, in the apparatus represented in the picture. Phenolphthalein is added. At the beginning, the solution was colorless, but in the end, the solution in the right prong became violet, and the solution in the left prong became brown. When a sample from the left prong gets dried, purple vapors are obtained. The product in the right prong consist of 28.6% of oxygen. What salt was used?

I suppose that the purple vapors represent iodine, and that the purple solution got that color because of phenolphthalein. Why is the other solution brown? How to use the oxygen mass share data?

[Borek]

I₃^- is brown.

[Rutherford]

Then the I₂ produced by hydrolysis reacted with I^- to from I₃^-. Thanks very much. Somehow I figured out the other part, so I don't need help here anymore. If someone is interested in the answer, it is KI.