Chapter 2

Matter and Change

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2.1 Properties of Matter

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2.2 Mixtures

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2.3 Elements and Compounds

2.4 Chemical Reactions

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Coffee is often brewed by mixing hot water with ground coffee beans.

CHEMISTRY & YOU

Why aren't there coffee grounds in a cup of coffee?

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Classifying Mixtures

Describing Matter

How can mixtures be classified?

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Describing Matter

• A salad bar provides a range of items, such as lettuce, tomatoes, cheese, and green peppers.
• Customers choose which items to use in their salads and how much of each item to use.
• So, each salad mixture has different types and amounts of components.

• A mixture is a physical blend of two or more components.

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Describing Matter

Most samples of matter are mixtures.

• Some mixtures are easier to recognize than others.
• You can easily recognize chicken noodle soup as a mixture of chicken, noodles, and broth.

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Describing Matter

Recognizing air as a mixture of gases is more difficult.

• But the fact that air can be drier or more humid shows that the amount of one component of air—water vapor—can vary.

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Describing Matter

Based on the distribution of their components, mixtures can be classified as heterogeneous mixtures or homogeneous mixtures.

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Describing Matter

Heterogeneous Mixtures

In chicken noodle soup, the ingredients in the soup are not evenly distributed throughout the mixture.

• There is likely to be different amounts of chicken and noodles in each spoonful.

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Describing Matter

A mixture in which the composition is not uniform throughout is a heterogeneous mixture.

Heterogeneous Mixtures

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Describing Matter

Homogeneous Mixtures

The substances in the olive oil are evenly distributed throughout the mixture.

• So, olive oil doesn’t look like a mixture.

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Describing Matter

Homogeneous Mixtures

The same is true for vinegar.

• Vinegar is a mixture of water and acetic acid, which dissolves in the water.

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Describing Matter

Homogeneous Mixtures

Olive oil and vinegar are homogeneous mixtures.

• A homogeneous mixture is a mixture in which the composition is uniform throughout.

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Describing Matter

Homogeneous Mixtures

Olive oil and vinegar are homogeneous mixtures.

• A homogeneous mixture is a mixture in which the composition is uniform throughout.

• Another name for a homogeneous mixture is a solution.

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Describing Matter

Homogeneous Mixtures

Many solutions are liquids.

• But some are gases, like air.
• And some are solids, like stainless steel, which is a mixture of iron, chromium, and nickel.

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Describing Matter

Homogeneous Mixtures

The term phase is used to describe any part of a sample with uniform composition and properties.

• By definition, a homogeneous mixture consists of a single phase.

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Describing Matter

• When oil and vinegar are mixed, they form a heterogeneous mixture with two layers, or phases.
• The oil phase floats on the water, or vinegar, phase.

A heterogeneous mixture consists of two or more phases.

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At the beach, you realize that both ocean water and sand are mixtures. Which is a homogeneous mixture (or solution)? Which is a heterogeneous mixture?

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At the beach, you realize that both ocean water and sand are mixtures. Which is a homogeneous mixture (or solution)? Which is a heterogeneous mixture?

Salt water is a homogeneous mixture, or solution. Sand is a heterogeneous mixture.

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Separating Mixtures

Separating Mixtures

How can mixtures be separated?

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Separating Mixtures

If you have a salad containing an ingredient you don't like, you can remove it with a fork.

• Many mixtures are not as easy to separate.

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Separating Mixtures

• To separate a mixture of olive oil and vinegar, for example, you could decant, or pour off, the oil layer.
• Or, you might cool the mixture until the oil turned solid.

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Separating Mixtures

• To separate a mixture of olive oil and vinegar, for example, you could decant, or pour off, the oil layer.
• Or, you might cool the mixture until the oil turned solid.

• Pouring off the oil layer takes advantage of the fact that oil floats on water.
• Cooling until the oil layer turns solid takes advantage of a difference in the temperatures at which the olive oil and vinegar freeze.

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Separating Mixtures

Differences in physical properties can be used to separate mixtures.

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Filtration

Separating Mixtures

The coffee filter at right can separate ground coffee beans from brewed coffee.

• The liquid brewed coffee passes through the paper filter, but the solid coffee grounds cannot pass through the filter.

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Filtration

Separating Mixtures

Filter paper used in a laboratory is similar to coffee filters.

• Filter paper is often placed in a funnel.
• Then the mixture is poured into the funnel.
• Solid particles that cannot pass through the filter remain in the funnel.
• The rest of the particles pass through.

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Filtration

Separating Mixtures

The process that separates a solid from a liquid in a heterogeneous mixture is called filtration.

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CHEMISTRY & YOU

Brewed coffee is a mixture of ground coffee beans and water. What process is used to separate ground coffee beans from brewed coffee?

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CHEMISTRY & YOU

Brewed coffee is a mixture of ground coffee beans and water. What process is used to separate ground coffee beans from brewed coffee?

Filtration is used to separate ground coffee beans from brewed coffee.

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Distillation

Separating Mixtures

Tap water is a homogeneous mixture of water and substances that are dissolved in the water.

• One way to separate water from the other components in tap water is through a process called distillation.

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Distillation

Separating Mixtures

During a distillation, a liquid is boiled to produce a vapor that is then condensed into a liquid.

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Distillation

Separating Mixtures

The figure below shows an apparatus used to perform a small-scale distillation.

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Distillation

Separating Mixtures

As water in the distillation flask is heated, water vapor forms, rises in the flask, and passes into a glass tube in the condenser.

• The tube is surrounded by cold water, which cools the vapor to a temperature at which it turns back into a liquid.

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Distillation

Separating Mixtures

As water in the distillation flask is heated, water vapor forms, rises in the flask, and passes into a glass tube in the condenser.

• The tube is surrounded by cold water, which cools the vapor to a temperature at which it turns back into a liquid.

• The liquid water is collected in a second flask.

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Distillation

Separating Mixtures

The solid substances that were dissolved in the water remain in the distillation flask.

• This is because their boiling points are much higher than the boiling point of water.

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Sample Problem 2.1

Separating a Heterogeneous Mixture

How could a mixture of aluminum nails and iron nails be separated?

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In order to identify how to separate aluminum and iron nails, the properties of both aluminum and iron must be known.

Sample Problem 2.1

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Sample Problem 2.1

List the properties of each substance in the mixture.

Aluminum

• metal
• gray color
• doesn’t dissolve in water
• not attracted to magnet

Iron

• metal
• gray color
• doesn’t dissolve in water
• attracted to magnet

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Sample Problem 2.1

Identify a property that can be used to separate different substances from each other.

• The ability to be attracted by a magnet is a property that iron and aluminum do not share.
• You could use a magnet to remove the iron nails from a mixture of iron and aluminum.

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Which physical property does filtration rely on to separate mixtures? Which does distillation rely on?

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Which physical property does filtration rely on to separate mixtures? Which does distillation rely on?

Filtration relies on the size of a particle, or molecule, of a substance. Distillation relies on the boiling point of the substance.

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Key Concepts

Mixtures can be classified as heterogeneous mixtures or as homogeneous mixtures, based on the distribution of their components.

Differences in physical properties can be used to separate mixtures.

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Glossary Terms

• mixture: a physical blend of two or more substances that are not chemically combined
• heterogeneous mixture: a mixture that is not uniform in composition; components are not evenly distributed throughout the mixture
• homogeneous mixture: a mixture that is uniform in composition; components are evenly distributed and not easily distinguished
• solution: a homogeneous mixture; consists of solutes dissolved in a solvent

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Glossary Terms

• phase: any part of a sample with uniform composition and properties
• filtration: a process that separates a solid from the liquid in a heterogeneous mixture
• distillation: a process used to separate components of a mixture using differences in boiling points

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END OF 2.2

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