Unit 2 Review

Pure Substances and Mixtures

Middle School

Key Vocabulary

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Pure Substance

A material with a fixed chemical composition and properties that cannot be physically separated.

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Mixture

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

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Element

A pure substance made of only one type of atom that cannot be broken down.

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Compound

A pure substance made of two or more elements chemically bonded in a fixed ratio.

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Homogeneous Mixture

A mixture with a uniform composition where the different components are not visible.

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Heterogeneous Mixture

A mixture with a non-uniform composition where you can easily see the different parts.

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Types of Pure Substances

Elements

• An element is a pure substance that consists of only one type of atom.

• Elements cannot be broken down into simpler substances through any chemical reactions.

• Examples of elements include iron (Fe), oxygen (O), and aluminum (Al).

Compounds

• A compound is a pure substance made of two or more elements chemically bonded together.

• The properties of a compound are very different from its constituent elements.

• For example, water (H₂O) is a liquid formed from two gases, hydrogen and oxygen.

Multiple Choice

What is the fundamental difference between an element and a compound?

• Elements are part of mixtures; compounds are not.

• Elements have one type of atom; compounds have two or more elements chemically combined.

• Elements are liquids; compounds are solids.

• Elements can be broken down; compounds cannot.

Multiple Select

Select all of the ELEMENTS from the list below.

• Water

• Aluminum

• Oxygen

• Air

• Copper

Multiple Select

Select all of the ELEMENTS shown below.

Multiple Choice

Which best describes ELEMENTS?

• made of only 1 type of atom

• made of 2 or more types of atoms

Multiple Choice

Which describes COMPOUNDS?

• made of one type of atom

• made of two or more types of atoms

Multiple Select

Select all the COMPOUNDS from the list below.

• Table Salt (NaCl)

• Air

• Oxygen (O₂)

• Carbon Monoxide (CO)

• Baking Soda

Multiple Select

Select all the COMPOUNDS shown below.

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Types of Mixtures

Homogeneous Mixtures

• These mixtures have a uniform composition, so you cannot see the different parts inside of them.

• They look like a single substance and are also known by the name of solutions.

• Some examples of these mixtures include air, saltwater, and metal alloys like brass.

Heterogeneous Mixtures

• These mixtures have a non-uniform composition, and you can easily see the different components.

• The different substances in the mixture remain distinct and are not mixed together evenly.

• Examples include a salad, a mixture of sand and water, or oil and water.

Multiple Choice

What does hetero mean?

• same

• different

• equal

Multiple Choice

What does homo mean?

• same

• different

• equal

Multiple Select

Which of the following are homogeneous mixtures? (Choose all that are correct!)

• cereal with milk

• chocolate chip icecream

• salt water

• pizza

• Soda

Multiple Choice

Which of the following is a heterogeneous mixture?

• salt water

• sugar water

• soda

• beach sand

Multiple Choice

What type of mixture is this?

• heterogeneous

• homogeneous

Multiple Choice

What type of mixture is this?

• heterogeneous

• homogeneous

Multiple Choice

Salad is a...

• homogeneous mixture

• heterogeneous mixture

Multiple Choice

Chicken noodle soup is a...

• homogeneous mixture

• heterogeneous mixture

Multiple Choice

What type of mixture is this?

• heterogeneous

• homogeneous

Physical and Chemical Changes

Middle School

Multiple Choice

Which of the following is the best definition of a physical change?

• A change that alters a substance's form but not its chemical identity.

• A change that creates a completely new substance with different properties.

• A change that can only happen when a substance melts or boils.

• A change that is permanent and cannot be reversed.

Multiple Select

Choose all of the following that are PHYSICAL changes.

Multiple Choice

melting ice cream

• physical change
• chemical change

Multiple Choice

Sugar dissolving in tea

• Physical Change
• Chemical Change

Multiple Choice

Cutting Paper

• Physical Change
• Chemical Change

Multiple Choice

Color is what type of property?

• Physical

• Chemical

Multiple Choice

Physical Properties are

• chemical changes

• are properties that can be observed without changing the matter's identity

• are properties that can be observed that change the matter into new matter with new properties

Multiple Choice

A property of matter that involves pounding a substance into thin sheets.

• solubility

• state

• malleability

• density

Multiple Choice

Mass, relative density, solubility, color, texture, and conductivity, are all examples of what?

• Physical state
• Insulators
• Physical Properties 
• Inferences

Multiple Choice

Is burning wood a chemical or physical change?

• chemical
• physical

Multiple Choice

glass breaking

• physical change
• chemical change

Multiple Choice

Iron rusts.

• Chemical change
• Physical Change

Multiple Choice

a copper penny turning greenish after a few years.

• Chemical Change
• Physical Change

Multiple Choice

which of these example is a physical change?

Multiple Choice

Exploding fireworks is a

• Physical Change

• Chemical Change

• Katy Perry Song