What is a heterogeneous, homogeneous mixture and or pure substances?

Question

wood??

water??

fluorine??

air??

hydrochloric acid??

marble??

pepsi??

frosted cupcakes??

milk??

and WHY??

Answer 1

A heterogeneous mixture has varied composition meaning your elements/matter is not uniform throughout. Such as HCl acid, marble, pepsi, frosted cupcakes, water. A homogeneous mixture is one that is the same composition throughout. Such as wood, milk. A pure substance is composed of only a single type of atom or molecule, such as Fluorine. Its always 100% pure. To answer Why? for these examples, ask yourself, What is the substance made of?

Answer 2

Here's a start - the link below provides a great explanation of what constitutes each

Question #1: All matter can be separated into two categories by asking the question "Is only one chemical substance present in the sample being considered?"

YES - Pure Substance

NO - Mixture

Question #3: All mixtures can be separated into two categories based on the question "Is the sample of constant composition?"

YES - Homogeneous mixture

NO - Heterogeneous mixture

Constant composition means that all parts of the mixture are the same. For example, dissolve sugar in water and mix it completely. Now take several samples from random areas. They will be the same, therefore this is a homogeneous mixture. Take some sand and some water and mix it up well. Take some samples and MAYBE they are the same. Allow the water to stand undisturbed and then sample it. One portion will be more sand than water and another will be more water than sand. This is heterogeneous.

Homogeneous mixtures do not settle out upon standing undisturbed and they cannot be separated by filtering or centrifuging. There are two broad categories of homogeneous mixtures.

From the second link

There are very few pure substances in nature. Dirt, rocks, sticks, bones, and even air are complex mixtures. In order to fully understand chemical reactions (like the combustion of wood), we need to be able to classify materials according to their purity

Almost everything in nature is heterogeneous, that is, its composition is not uniform. Wood is a good example. If you look at a cross section of a piece of wood, the rings are immediately apparent. These rings are alternating bands of light and dark colored wood which were laid down as the tree grew. This variation in the composition of the wood from one place in the sample to another is what makes it heterogeneous. If you further examine the wood under a microscope you will find that even within a single band the wood is non-uniform, with fibers composed of chains of tiny boxes; the remains of living plant cells. Wood, then, is heterogeneous through and through as is typical for natural substances.

A few natural substances are homogeneous, that is, their composition is uniform. Air is an example of such a substance. If you look at a sample of air, its composition is the same from place to place within the sample.

Answer 3

A pure substance contains only one type of molecule (water [H2O], fluorine [F2], hydrochloric acid [HCl], marble [CaCO3])

An homogeneous mixture looks like it contains only one substance, but actually has more than one type of molecule (air [O2, and N2, etc],

pepsi in a closed bottle [water, CO2, carbonic acid, colouring, and flavouring, etc]

Heterogenous mixtures look like more than one type of molecule is in them (wood,  frosted cupcakes, milk[use a microscope)