hard chemistry plz detail

Copper carbonate is precipitated by combining aqueous solutions of copper(II) and sodium carbonate. Copper basic carbonate precipitates from the solution:
2 CuSO4 + 2 Na2CO3 + H2O → Cu2(OH)2CO3 + 2 Na2SO4 + CO2

Then the concentration of Cu2+ is tremendously lowered that Cu metal tends to lose electrons to replenish the Cu2+ ions in solution. The overall emf will be much reduced (less and less positive).