Mixtures and Solutions

Mixtures and Solutions

Middle School

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Learning Objectives

• Explain the difference between pure substances and mixtures.

• Describe homogeneous and heterogeneous mixtures and tell them apart.

• Identify and classify different examples of mixtures.

• Understand that solutions are a special kind of homogeneous mixture.

Key Vocabulary

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Mixture

A physical combination of two or more substances that are not chemically bonded together.

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Pure Substance

A substance with definite physical and chemical properties, made of only one type of particle.

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Homogeneous Mixture

A mixture with a uniform composition that appears the same throughout all of its parts.

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Heterogeneous Mixture

A mixture with a non-uniform composition where the different components can be easily seen.

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Solution

A specific type of homogeneous mixture where one substance dissolves into another substance completely.

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Pure Substances vs. Mixtures

Pure Substances

• Pure substances consist of only one type of particle, either an element or a compound.

• They possess definite physical and chemical properties that are always the same for that substance.

• The particles are chemically bonded and cannot be separated by any simple physical methods.

Mixtures

• Mixtures are a physical combination of two or more substances that are not chemically bonded.

• Each substance in a mixture keeps its own unique identity and original chemical and physical properties.

• The different components of a mixture can often be separated by using simple physical changes.

Multiple Choice

What is the main difference between a pure substance and a mixture?

• Pure substances can be separated by physical methods, while mixtures cannot.

• Pure substances are always solids, while mixtures are always liquids.

• The particles in a pure substance are chemically bonded, while they are not in a mixture.

• Mixtures have definite properties that are always the same, while pure substances do not.

Multiple Choice

How do the properties of the substances in a mixture compare to the properties of a pure substance?

• In a mixture, each substance keeps its own properties; in a pure substance, the properties are new and definite.

• In a pure substance, each element keeps its own properties; in a mixture, the properties are always the same.

• The properties of substances in a mixture are always the same, while a pure substance has changing properties.

• The properties of all substances change completely when they form a mixture or a pure substance.

Multiple Choice

A student has a liquid that is heated. The liquid boils, and a white, solid powder is left behind. What can the student conclude about the original liquid?

• It was a mixture because the substances were chemically bonded together.

• It was a pure substance because heating it caused a chemical change.

• It was a mixture because its components were separated by a physical change.

• It was a pure substance because it consisted of only one type of particle.

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Types of Mixtures

Homogeneous Mixture

• ​This mixture has a uniform composition, meaning it looks the same all the way through.

• ​​The different parts that make up the mixture are not visible to the naked eye.

• ​Examples include chocolate milk, dishwasher soap, and water with food coloring.

Heterogeneous Mixture

• ​This mixture does not have a uniform composition, so it looks different throughout.

• ​​You can easily see the different components or layers that make up the mixture.

• ​Some examples are a salad, a mix of sand and sugar, and a bowl of M&Ms.

Multiple Choice

What is the key characteristic of a homogeneous mixture?

• The components are layered and separate easily

• The different parts are large enough to see

• It has a uniform composition throughout

• It is always made of a solid and a liquid

Multiple Choice

Why is a salad considered a heterogeneous mixture?

• Because it has a uniform look all the way through

• Because all the ingredients are the same color

• Because you can easily see the different ingredients

• Because it tastes good with dressing

Multiple Choice

If you stir a spoonful of sugar into a glass of water until you can no longer see the sugar, what have you created and why?

• A homogeneous mixture, because the water is now sweet.

• A heterogeneous mixture, because it contains a solid and a liquid.

• A homogeneous mixture, because it looks the same throughout.

• A heterogeneous mixture, because you can still separate the sugar.

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Common Misconceptions About Mixtures

Misconception	Correction
All mixtures look the same throughout.	Only homogeneous mixtures have a uniform look. Heterogeneous mixtures do not.
Mixing things always creates a new substance.	In a mixture, substances keep their original properties.
Solutions are not a type of mixture.	Solutions are a special type of homogeneous mixture.

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Summary

• Mixtures are physical combinations of substances that are not chemically bonded.

• Substances within a mixture retain their original properties.

• Homogeneous mixtures are uniform, while heterogeneous mixtures have visible parts.

• Mixtures are not pure substances and can be separated by physical means.

Poll

On a scale of 1-4, how confident are you about distinguishing between different types of mixtures?

• 1

• 2

• 3

• 4