# If pizzas are an example of a heterogeneous mixture, then what kind of heterogeneous mixture are they?

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There are two primary types of mixtures which include homogeneous and heterogeneous mixtures.

Homogeneous Mixtures – These are mixtures which are uniform in appearance. The concentration of the dissolved substance(s) is constant throughout the mixture. Suppose that you dissolved a teaspoon of sugar within a warm glass of water and stirred its contents until no more solid sugar was observed. Once the sugar solution appears clear and colorless, we have created an example of a homogeneous mixture. The concentration of sugar within this solution would be constant throughout.

Heterogeneous Mixtures – These are mixtures which are not uniform in appearance. The concentration of substance(s) within such a mixtures is not constant throughout the mixture. Each constituent substance is not distributed evenly. Suppose that you emptied a bag of assorted nuts, candy, and popcorn into a basket. Upon stirring of this basket, one would observe an example of a heterogeneous mixtures. The concentration of nuts, candy, and popcorn would not be expected to be constant throughout.

What about pizza?

Let us assume that we are dealing with a pizza containing the following constituents:

• Round circular bread dough
• Tomato sauce on top
• Mozzarella
• Peperoni
• Sausage
• Red and green pepper slices
• Anchovies

When the pizza maker places on top of the tomato sauce the mozzarella, peperoni, sausage, red and green peppers, and anchovies, there is usually no specific pattern that he uses to place these constituents onto the pizza. We can assume that their placement is random. Thus, the final product that is obtained is a heterogeneous mixture. The concentration of each constituent is not constant throughout the pizza.

What type of heterogeneous mixture is pizza?

This is a puzzling question since the usual types of heterogeneous mixtures that one encounters include suspensions and colloids.

Heterogeneous Suspension Mixtures – These are heterogeneous mixtures which are not uniform where component constituents may settle out of solution if left undisturbed. There is a tendency for separate layers to form if the mixture is left undisturbed. An example would include attempting to mix water and sand. Once the mixing stops, sand will settle at the bottom of the container.

Heterogeneous Colloidal Mixture – These are heterogeneous mixtures which may appear to be uniform where component substances are suspended in solution rather than fully dissolved. The primary difference between suspensions and colloidal mixtures is that the component substances will not settle out of solution within colloidal mixtures. It is not possible to filter out component substances within colloidal mixtures. An example would include milk.

The question that was posed suggests that we must choose one of these designations for the pizza. By process of elimination, it is safe to say that pizza is not a heterogeneous colloidal mixture. It would certainly be possible to filter (remove) constituents like peperoni out of this mixture. To that end, can pizza be treated as a heterogeneous suspension mixture? If one treats the dough as the container, the tomato sauce as the solvent, and the mozzarella, peperoni, sausage, red and green pepper slices, and anchovies as the mixture components, one could make the argument that these components will never actually dissolve into the tomato sauce and thus will always settle on top of the solvent tomato sauce. Thus, one may conclude that pizza can be treated as a heterogeneous colloidal mixture.

After all of this pizza talk, I need to have a slice of pizza.

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