Help Session on Standard MNRG.4

This standard states:

I am able to categorize a sample of matter as one of the following:

  • Heterogeneous mixture
  • Homogeneous mixture
  • Compound
  • Element

To show the difference, I started out with some quick visual definitions:

element

Elements have their own spot on the periodic table.

An element is the purest form of matter.  Anything that has it’s own spot on the periodic table of the elements is an element.

If two or more elements combine in a chemical reaction, they will form a new type of pure substance that has a distinct ratio of amounts one element to another.

Just because two elements are mixed together doesn’t mean that a compound has formed.  There must be a chemical reaction that produces something completely new.

compound image

Compounds form in chemical reactions between elements.

When two or more substances are placed together and don’t react chemically, the result is what we call a mixture.  Sometimes, it’s obvious that what we have is a mixture, because we can see it by eye.  Mixtures like this are called heterogeneous mixtures (“hetero-” = different):

hetero_mixture_image

Heterogeneous mixtures appear to be mixtures by eye.

Sometimes, the particles in the mixture are so small that we can’t really tell they are mixtures, unless we know for sure.  These mixtures are called solutions or homogeneous mixtures (“homo-” = same).  Homogeneous mixtures are easy to confuse with pure substances, just by looking at them:

homo_mixture_image

Homogeneous mixtures look like pure substances by eye.

Next, we looked at real life examples of these classes of matter.

copper image

Copper is an example of an element because it is on the periodic table.

water_image

Pure (distilled) water is an example of a compound because H2O is a definite ratio of elements.

bean_salad_image

This bean salad is a heterogeneous mixture because you can easily see with your eye that it contains more than one type of substance.

KoolAid_ image

This Kool-Aid is a homogeneous mixture because it is made of more than one substance, but I can’t tell that just by looking at it.

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