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Mixtures and Pure Substances
Heterogeneous or homogeneous?
We found out in the lab that they were all Heterogeneous (even
though some looked homogeneous)
So is everythingheterogeneous?
Isn’t anythinghomogeneous?
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
Heterogeneous materials - can see two parts
Mechanical Mixtures
Matter
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
But what aboutpure things?
Isn’t anythingreally pure?
Or is everything just mixed together so well we can’t see the parts?
Solutions
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.
Heterogeneous materials - can see two parts
Mechanical Mixtures
Matter
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 substancesYou can only see one thing because there is only one kind of particle in
it.