Classification of Matter

In Chem we were going through the Chemistry program to check what we remember and what we don't remember. We were meant to quiz each other in pairs, but I had another idea (i.e. writing it up on a blog). Here I go...

This post will be a quickie because the first heading on my program only has two dot points underneath it which kind of overlap anyway.

So... pure substances and mixtures. What's the difference?

Well, a pure substance is made up of entirely one thing- whether it be one element, or one compound. An example would be pure gold, which is made up entirely of the atom Au. Another example would be a salt crystal which is made up entirely of NaCl. A mixture is made up of multiple pure substances. An example would be a salt solution because that has both NaCl and H₂O.

Pure substances and mixtures can be broken down further. Pure substances, as alluded to before, can be broken up into elements and compounds. Elements only have one type of atom (e.g. Fe, Au, Ag, C) while compounds have multiple different types of atoms (e.g. CO, NaCl). Meanwhile, mixtures can be broken down into homogeneous and heterogeneous mixtures. (By the way, the only way I was able to spell those two words correctly is because Google Chrome has spell check.)

Both kinds of mixtures are made up of multiple pure substances mixed together. The difference between homogeneous and heterogeneous mixtures, however, is whether or not the proportion between pure substances changes throughout the mixture. In a homogeneous mixture (homo = same), the proportion between pure substances is the same throughout the whole mixture. An example would be salt water- the ratio between salt and water is the same no matter which part of the mixture you're looking at. In a heterogeneous mixture, on the other hand, the proportion between pure substances might change throughout the mixture. An example would be a choc-chip biscuit. The ratio between chocolate chips and biscuit dough differs depending on which part of the biscuit you're looking at.

Generally, if you can see the parts which make up a mixture, it's probably a heterogeneous mixture. If you can't, it's probably a homogeneous mixture.