To present the difference in oxidizing strength in concentrated and dilute nitric acid reacting with copper, a simple, facile demonstration of these reactions is designed using a waste plastic bottle, plastic droppers, and syringes, which are costless and easily assembled. This new version can be used to demonstrate the difference in oxidizing strength of concentrated and dilute nitric acid successively in a safe way. The experimental phenomena are obvious, and the amounts of used reagents are small, preventing the hazards from hurting the instructors/students or contaminating the atmosphere. It only takes the instructors about 2 min to show the whole experimental process, which can be controlled according to instructors' teaching plan. This demonstration is very visible, convenient, moveable/portable, and easily operated.