Mixtures and Pure Substances

Heterogeneous or homogeneous? We found out in the lab that they were all Heterogeneous (even though some looked homogeneous)

Isn’t anything homogeneous? So is everything heterogeneous?

Experiment – add kool-aid to water

We added two different materials! Can this mixture be classified as heterogeneous? No, because after we’ve finished mixing it together we can see only one part. It has only one set of properties. We call this homogeneous mixture a solution

A homogeneous mixture or solution is a mixture that appears the same all over -- the different materials are not visible. The parts of a solution will not ‘settle out’ (like fat in milk) Solutions can be solids, liquids, or gases

Some examples of common solutions: Solid solution: Tooth filling: silver + tin + mercury Gas solution: Air: Nitrogen + Oxygen + other gases Liquid solution: Ocean/Seawater: salt + water

A mechanical mixture is a mixture in which the different parts can be seen easily with the unaided eye. When materials are mixed together but we can still see the different parts we call it a mechanical mixture

Homogeneous mixtures (solutions) Matter Heterogeneous materials - can see two parts Mechanical Mixtures Homogeneous materials can see only one thing - one set of properties Homogeneous mixtures (solutions) They’re mixed together so well you only see one thing – it looks pure but it isn’t

Or is everything just mixed together so well we can’t see the parts? Solutions But what about pure things? Isn’t anything really pure?

PURE THINGS Yes, pure things exist too! The properties of various mixtures and substances are explained by the particle theory of matter: - all matter is made up of extremely small particles - each pure substance has its own kind of particle (atoms or molecules), different from the particles of other pure substances.

A pure substance is any material made up of only one kind of extremely small particle (either an atom or a molecule). A pure substance: - is always homogeneous - has the same properties no matter where in the world it is found.

Homogeneous mixtures (solutions) Pure substances Matter Heterogeneous materials - can see two parts Mechanical Mixtures Homogeneous materials can see only one thing - one set of properties Homogeneous mixtures (solutions) They’re mixed together so well you only see one thing – it looks pure but it isn’t Pure substances You can only see one thing because there is only one kind of particle in it.