Question

Is it redundant to say that a pure substance is homogeneous, or can it not be both at the same time, (since homogeneous implies that we're talking about a mixture)?

Answer 1

Chemically, a pure substance is the one that cannot be separated into its constituents by physical methods. So, a pure substance can either be an element or a compound.

In general sense, elements and compounds have fixed and uniform composition throughout the bulk. But under special conditions they may act like heterogeneous substances like water at 20 °C is a homogeneous liquid but at 0 °C it is in equilibrium with ice i.e., partially frozen and now it will act like a "heterogeneous substance".

So in general you can skip the word "homogeneous" while describing our substances, but depending upon the context this word may not be redundant.