To effectively demonstrate the transformation of ethanol into acetaldehyde, a simple, low-cost, and eco-friendly reaction demonstration was designed, in which a Y-shaped tube served as the reactor, condenser, and detector with the help of specific reagents. The ethanol was added via a transparent elephant nose spray bottle fixed to the top of the stopper and reacted with the thin layer of commercially available copper(II) oxide, leading to the formation of a red copper mirror in the left arm of the Y-shaped tube. The product of the oxidation could be directly detected by the color change of the Schiff reagent. The vapor of the product was condensed by the mixture of silver oxide and ammoniacal-silver solution in the right arm of a Y-shaped tube and reacted with them, resulting in the formation of bright silver mirror. The transformation process from ethanol to acetaldehyde is carried out in an experimental setup, which is easy to assemble and simple to operate. The demonstration consumes small amounts of chemicals without releasing toxic fumes. 94% of the students who took part in this demonstration highly rated this demonstration.