During the electrolysis of an aqueous solution of copper (II) nitrate, a metal was released at the cathode. The metal was heated with copper (II) oxide, and a red compound was formed. This compound was treated with the required amount of concentrated sulfuric acid while heating, and the evolution of a pungent gas was observed. When sodium sulfide was added to the resulting solution, a black precipitate formed. Write the equations for the four reactions described.
2Cu (NO3) 2 + 2H2O = 2Cu + O2 + 4HNO3 (electrolysis)
Cu + CuO -> Cu2O
Cu2O + 3H2SO4 -> 2CuSO4 + SO2 ↑ + 3H2O
CuSO4 + Na2S = CuS ↓ + Na2SO4
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