This is an IChO problem, and I think that it deserves more attention because it is really challenging, so I opened this topic:
The substance X has been prepared by the following procedures. Copper(II) sulfate pentahydrate (ca 10 g) was dissolved in a mixture of distilled water (80 cm3) and concentrated sulfuric acid (4 cm3). The solution was boiled with analytical-grade metallic tin (10 g) until the solution became colorless and the deposited copper was covered with a grey coating of tin.
The resultant solution was filtered and treated with an ammonia-water solution until the complete precipitation of a product. It was filtered off and washed with water until no odor of ammonia was detectable. The precipitate obtained was added to the nitric acid solution gradually in small portions, with stirring, until the solution was saturated. The suspension was boiled for 2 min, filtered into a warm, insulated flask and allowed to cool slowly. The 1.05 g of crystalline product X was obtained.
Under heating X rapidly decomposes with the mass loss of 17.49%. The residue formed is a binary compound identical with the common mineral of tin. The volatile decomposition products passed over 1.00 g of anhydrous copper(II) sulfate increase its mass by 6.9%.
Attempt:
When the salt was dissolved I ended with Cu2+ ions. When tin was added the color disappeared , meaning that Cu2+ reduced to Cu+. Some copper even reduced to metal Cu and it deposited with a little tin. The rest of the tin was oxidized. The next part I don't understand. Why is ammonia added and then removed with water? Why was nitric acid added-to oxidize Sn2+ to Sn4+ maybe?