Week 1: Chemistry Quiz

Well, out of 12 potential questions, I got 3 wrong answers. Not great considering it’s 25% of the material covered in the lesson. This chemical change versus physical change and homogeneous versus non is more difficult to understand in practice, than it seemed at first. I understand now how burning wood is a chemical change -not- physical and dissolving sugar is physical -not chemcial.

But, I still don’t understand how coffee is a homogeneous substance, like water though. According to coffee-tea.co.uk, “There are many compounds in coffee that are often thought to have implications upon human health; these include Caffeine, micronutrients, LDL cholesterols and chlorogenic acid.” So, I don’t really understand how that is homogeneous (dictionary definition: unvarying, alike, similar, identical), yet impure? I understand how Salt is impure (because besides NaCl it can also contain trace amounts of minerals, depending on the source where it is mined) and I think that also makes it non-homogeneous. I’m just having trouble wrapping my head around the coffee question…