① In order to remove the gas in the syringe, it is necessary to push the plug to inject water into the needle, so the answer is: push the plug to inject water into the needle;
(2) Nitric acid has strong oxidizability, which can oxidize copper to generate copper nitrate, and the solution is blue to generate colorless gas NO, and the ionic equation of the reaction is 3cu+8h+2no3-= 3cu2+2no ↑+4h2o.
So, the answer is: colorless; 3Cu+8h++ 2 NO3-= 3c U2 ++ 2NO ↑+ 4H2O；
(3) Verification of NO can be achieved by using it to be easily oxidized by oxygen to generate reddish-brown nitrogen dioxide. The method is to pump air into the syringe, and the gas changes from colorless to reddish brown.
So the answer is: when air is pumped into the syringe, the gas changes from colorless to reddish brown;
(2)① Because there is too much nitric acid in the reaction, the mass of copper is equal, that is, the concentration of copper nitrate generated is the same.
So the answer is: disagree; The same mass of copper reacts with the same volume of excess nitric acid to produce the same copper ion concentration;
(2) Nitric acid is unstable. Under the condition of heating, it will also decompose to generate nitrogen dioxide, which will react with oxygen to generate nitric acid. The reaction equation is 4NO2+O2+2H2O = 4NO3.
So the answer is: excessive nitric acid decomposition will produce reddish-brown NO2；; 4 NO2+O2+2H2O = 4 HNO 3；
Scheme 1 and scheme 3 both cause environmental pollution, and scheme 2 is the best, so the answer is scheme 2.