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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2008-07-21 17:54:38 補充：
為甚麼在課本上未見過這麼評細的解說呢？

其實在香港所有教科書中，都沒有反應 (1)。是自己在重複的實驗中推論的。幾年前在會考曾經在類似的題目，只是問黑色固體是甚麼，亦沒有問方程式（equation）。

香港的教科書，主要目的是賺錢，開拓內容是一個可有而最好無的花錢部份。另一方面，許多學校選書的重點不是內容，而是書商提供給學校的『額外資源』。

因此，香港教科書的內容主要是以抄襲為主，而心思主要花在應酬所謂「教改」的要求上。

銅與濃硫酸的反應是傳統的課程，除非是課程上明確說明而求解釋氧化銅(II)的出現，或者會考曾深入問到反應的情況（或方程式），否則舊課本沒有的，新的課本不可能有。