Conc. Sulphuric acid+ copper ->observations??

The black solid is copper(II) oxide, CuO.

Cu reacts with concentrated sulphuric acid to give copper(II) sulphate.
Cu + 2H2SO4 → CuSO4 + 2H2O + SO2

This is a combination of two reactions: Firstly, copper reacts with concentrated sulphuric acid to give copper(II) oxide, and the reaction is redox. Secondly, copper(II) oxide reacts with concentrated sulphuric acid, and this reaction is neutralization.
(1) Cu + H2SO4­ → CuO + H2O + SO2
(2) CuO + H2SO4 → CuSO4 + H2O

The second reaction is neutralization, and the sulphuric acid needs water to undergo the neutralization. Since the sulphuric acid used is usually very concentrated (even 98%), there is insufficient amount of water to convert all the copper(II) oxide to copper(II) sulphate. Therefore, some copper(II) oxide is left unreacted and appears as a black solid.
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