Answer:
When you drop hydrochloric acid (HCl) solution into a test tube containing copper(II) oxide (CuO) powder, a chemical reaction occurs. This reaction is known as an acid-base reaction and involves the exchange of ions between the HCl solution and the CuO powder. Here's what happens:
1. CuO (copper(II) oxide) is a basic oxide, meaning it has the ability to react with acids.
2. HCl is an acid, which dissociates in water to produce hydrogen ions (H+) and chloride ions (Cl-).
3. When you add HCl solution to the test tube containing CuO powder, the following reaction takes place: CuO + 2HCl -> CuCl2 + H2O.
4. In this reaction, the CuO reacts with HCl to form copper(II) chloride (CuCl2) and water (H2O).
5. The copper(II) chloride formed may dissolve in the excess HCl solution, resulting in a greenish-blue solution.
It's important to handle chemicals with caution and perform this experiment in a controlled environment, following appropriate safety protocols.