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01_02 Classification of Matter by Composition

September 30, 2019


In our last lesson we looked at the classification of matter. We looked at it by state solid liquid and gas. In this lesson we’re going to look at it by what we call composition; ways of dividing up matter that’s different than solid liquid and gas. This is kind of a flowchart and we’ll examine it bit by bit of the way we can classify matter by composition. So we see the top box that says matter everything fits underneath this category of matter. And the question that it has underneath that is does it have variable composition? Well, we’re going to look at the left side of this flowchart and we’re going to examine the components there. A pure substance is the first box we see there, and a pure substance is made up of only one component. So it’s got only one thing throughout the whole substance. That is a pure substance, and it can be further subdivided into either being an element or compound. Let’s look first at an element. In an element it cannot be chemically broken down into any simpler substances. So it is the simplest form of matter and that is an element. We see here a picture of helium, helium is a gas that is in like a Goodyear blimp and it is only one kind of substance throughout the whole thing. A compound however can be broken down and it can be more simplified into two or maybe more of these elements okay. So they are a chemical composition of this that we’re going to talk about it’s a definite proportion. For our element we’ll see a periodic table that will be all the different elements and we’ll examine that really really closely but in an element all the atoms – and we will define atoms – are exactly the same. In a compound we’ve got two or more of these elements that are in these fixed ratios. So we have two or more atoms coming together of different varieties to make our compound. Now on the other side of this flowchart we have if it’s not a pure substance it’s going to have to be a mixture, and mixtures can then be further subcategorized. So what’s a mixture well if you have two or more of any of those components – whether they be elements or compounds – if you have two or more of those put together then it is going to be a mixture, and you can put those together in any type of proportion. So let’s just think of a mixture let’s take some salt and pepper okay I could put them together and if I put salt and pepper together I could put a little salt and I could put a lot of pepper, or I could put a little pepper and a lot of salt. So that could be in any proportion. If I were making sugar water I could put a little sugar in water and stir it up and dissolve that sugar and there’d be a little sugar in the water, or I could put more sugar into the water and stir it up and it’d be a mixture so the composition can vary if it’s a mixture. Now a mixture can either be a homogeneous mixture meaning it’s uniform throughout the whole thing. My example of sugar water would be a homogeneous mixture. If I stirred it up and I took a little sip of that water it would taste exactly the same as if I drank a little bit more a little bit more every sip with tastes the same because it’s uniform throughout. When I look at it I can’t distinguish different regions it looks the same throughout that is homogeneous. The other type of mixture is heterogeneous now a heterogeneous the composition varies throughout it. So if I were to take that salt and pepper example put them together I can visually look at that say hey there’s salt and there’s pepper and there’s salt I can distinguish those different regions in there. It’s visually very evident so the composition is not uniform throughout and that is a heterogeneous mixture. So we see this matter being subdivided into pure substance a mixture and then those are further divided out into other classification schemes. And again if we understand that something fits within one of these categories we can study that category and we can know something about that substance. Now let’s talk out this mixture when you have a mixture mixtures can always be separated out back again from each other by some kind of what we call physical means. So they can be ways of taking this mixture and saying let’s pull the parts away from each other. Now a nice picture that we see there is there’s some sand and some iron filings in that sand. All I have to do is take a magnet and put it over top of there and all the iron filings would be attracted to that magnet and that would separate it out by physical means. There is also an image there of a distillation apparatus and I want you to read about separating mixtures it’s on page eight in your book and it talks about various physical means by which you can separate it, and it will talk about the distillation and what that means and other means by which you can separate it. So take notes over that page of the separating mixtures and bring that to class with you next time.

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