The dark red powder is copper metal. At the strongly acidic conditions of your experiment you certainly don't get any oxide. This also explains why
nothing happened when you added hydrochloric acid to the red powder. The metal does not react with hydrochloric acid (at least not quickly, it does
react slowly in the presence of O2 besides the hydrochloric acid).
In the final step the metal is oxidized by the peroxide in the percarbonate and the acid. Probably you added some excess percarbonate and that gives a
blue precipitate with copper(II), of which a part is converted to copper peroxide (which is dark brown) if you have excess percarbonate added, so that
the liquid is alkaline.
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