If NaOH is added to the copper sulfate solution, if it does not oscillate, concentrated sodium hydroxide will appear locally and precipitation reaction will occur:

Copper sulfate+sodium hydroxide = copper hydroxide+sodium sulfate

But in some places where the concentration of sodium hydroxide is low, another relatively light-colored precipitate is basic copper sulfate:

2 cuso 4+2 NaOH = Cu2(OH)2so 4+na2so 4

Basic copper sulfate is easy to decompose, and black copper oxide will appear if heated;

Cu2(OH)2 SO4 (thermal) = CuO+CuSO4+H2O