Here's why:

* Pure Copper: Copper itself is an element, meaning it's made up of only one type of atom.

* Copper Pipe: Copper pipes are made by processing and shaping copper metal. However, they often contain small amounts of other elements like tin, zinc, and manganese. These elements are added to improve the copper's properties, like strength and resistance to corrosion.

Since the copper pipe contains more than one type of substance, it's considered a mixture rather than a pure compound.