Xiao Xin brought a piece of yellow metal to show off to his classmates that he had found gold. Bao Xiao said that he saw a copper-zinc alloy on the Internet, which looked like gold.

Phenomenon and Conclusion (1) Gold does not react with oxygen at high temperature, and the yellow metal turns black in the experiment, which shows that copper reacts with oxygen to produce black copper oxide, so Xiao Xin's guess is wrong, and the black substance is CuO；;

(2) When the yellow metal is put into dilute hydrochloric acid, the reaction between zinc and dilute hydrochloric acid will generate zinc chloride and hydrogen, so the phenomenon observed by Bao Xiao in the experiment is that bubbles are formed on the surface of the yellow metal, and the chemical equation is: Zn+2HCl ═ ZnCl2+H2 ↑;

Reflection and Application When yellow metal is put into silver nitrate solution, copper and zinc in copper-zinc alloy can replace silver in silver nitrate solution, so white material precipitates on the surface of yellow metal, which proves that yellow metal is copper-zinc alloy.

So the answer is: (1) is incorrect, CuO；;

(2) bubbles are formed on the surface of yellow metal, Zn+2HCl ═ ZnCl2+H2 ↑;

(3) Cut off a small piece of yellow metal and put it into silver nitrate solution. The phenomenon observed in the experiment is the precipitation of white material on the surface of yellow metal, which proves that yellow metal is copper-zinc alloy.