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Mixtures - Concept

Teacher/Instructor Jacqueline Spivey
Jacqueline Spivey

Ph.D.,U.C.Santa Cruz
Teaching at a top-ranked high school in SF

She teaches general and chemistry at a top-ranked high school in San Francisco. Prior to that, she lead and published a number of research studies and lectured at SF State University.

Mixtures are composed of pure substances and elements, but unlike compounds these substances retain their own chemical identities and properties. Mixtures can be homogeneous or heterogeneous. Homogeneous mixtures are the same throughout and are called solutions. Heterogeneous mixtures don t have uniform composition.

So this segment let's go ahead and discuss mixtures. So let's recap a little bit about how we classify and describe matter remembering that matter is anything that occupies space. So we're going to describe it based on the physical state or its composition so again the physical state are the things that you probably have encountered before, discussing whether something is a solid, a liquid or a gas.

But the composition is whether or not it's made up of elements or compounds or whether or not it's a mixture. So just to recap a little bit a compound is formed by having two or more elements. And remember elements are those guys that we find on the periodic table, they cannot be broken down any further. So most of the matter that we encounter consist of mixtures of different substances where each substance in a mixture retains its own chemical identity and therefore its own properties. So unlike pure substances the composition of mixtures can vary.

And so this is a good point to say that it will take you sometime to understand how to differentiate between things probably being different types of mixtures, so you should be patient with yourself. So the substances making up a mixture we call components of the mixture. So for instance I had a latte for breakfast and it was composed of milk, espresso and sugar. So mixtures can be separated into pure substances be they elements or compounds for example air is a mixture and it's composed of the element oxygen and nitrogen the compound water, the compound carbon dioxide, the element argon and many others.

Mixtures can further be classified as homogeneous or heterogeneous and so you should take these two words and apply them to this concept the same way that you've been applying them to others. So if something is homogenous that means it is the same throughout and it doesn't vary in composition from one region to another. And so a homogeneous mixture is what we refer to as a solution. So a heterogeneous mixture contains reagents that have different properties from each other. So that means is not uniform in nature, if you poured say sand into water you're going to mix it up for a couple of minutes there'll be some sand squiring around then they will both become separated from each other, so therefore it would be a heterogeneous mixture.