(1)C and CuO are black powder. In the process of heating with alcohol lamp, the powder in the test tube will turn red gradually because the copper is reduced.

(2) In the experiment, the purpose of alcohol lamp and net cover is to increase the heating temperature;

(3) The phenomenon in the test tube is that the clear limewater becomes turbid, because the carbon dioxide generated in the experiment reacts with calcium hydroxide to generate calcium carbonate precipitation and water, and the chemical equation of the reaction is CO2+Ca (OH) 2 = CaCO3 ↓+H2O.

So the answer is: (1) black powder turns red; ? (2) increase the temperature; ? ③CO2+Ca(OH)2 = CaCO3↓+H2O。