chemistry 20.1

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Chemistry 20.1

© Copyright Pearson Prentice Hall

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The Meaning of Oxidation and Reduction

Salt on icy roads can make driving safer, but the salt that clings to the metallic parts of cars can cause them to corrode or rust relatively quickly. This corrosion is one example of a chemical reaction called oxidation-reduction. You will learn about oxidation-reduction reactions.

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> What Are Oxidation and Reduction?

What Are Oxidation and Reduction?

How is the gain or loss of oxygen in a chemical reaction linked to oxidation and reduction?

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The substance gaining oxygen is oxidized, while the substance losing oxygen is reduced.

These reactions are called oxidation-reduction reactions and are also known as redox reactions.

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Oxygen and Redox

A Bunsen burner oxidizes the methane in natural gas to carbon dioxide and water.

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Carbon is oxidized when charcoal burns.

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Iron is oxidized when it rusts.

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Electron Shift in Redox Reactions

How is the gain or loss of electrons linked to oxidation and reduction?

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Losing electrons is oxidation. Gaining electrons is reduction.

• Oxidation is now defined to mean complete or partial loss of electrons or gain of oxygen.

• Reduction is now defined to mean complete or partial gain of electrons or loss of oxygen.

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Redox Reactions That Form Ions

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The substance that loses electrons is called the reducing agent. The substance that accepts electrons is called the oxidizing agent.

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Practice Problems for Conceptual Problem 20.1

Problem Solving 20.1 Solve Problem 1 with the help of an interactive guided tutorial.

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Redox With Covalent Compounds

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> Corrosion

Corrosion

What happens to iron when it corrodes?

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> Corrosion

Iron, a common construction metal often used in the form of the alloy steel, corrodes by being oxidized to ions of iron by oxygen.

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> Corrosion

Resistance to Corrosion

Aluminum resists corrosion because it forms a protective coating of aluminum oxide.

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> Corrosion

Controlling Corrosion

Painting a surface protects it from corrosion. Chromium metal also serves as a protective coating.

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> Corrosion

Zinc blocks attached to the steel hull of this ship oxidize instead of the iron, preventing corrosion.

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Section Quiz

-or-Continue to: Launch:

Assess students’ understanding of the concepts in Section

20.1 Section Quiz.

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20.1 Section Quiz.

1. Choose the correct words for the spaces. During oxidation, an element _______ electrons. During reduction, an element ________ electrons.

a. gains, loses

b. loses, gains

c. gains, donates

d. gains, accepts


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20.1 Section Quiz.

2. Choose the correct words for the spaces. During reduction, a substance may _______ oxygen or ________ hydrogen.

a. gain, lose

b. lose, gain

c. gain, gain

d. lose, lose


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20.1 Section Quiz..

3. The element that donates electrons in a redox reaction is called the reducing agent. This means the reducing agent is always

a. the more active element.

b. the less active element.

c. oxidized.

d. reduced.


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20.1 Section Quiz.

4. Which substance is the reducing agent in the following chemical reaction?

Fe2O3 + 3CO 2Fe + 3CO2

a. Fe2O3

b. CO

c. Fe

d. CO2


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20.1 Section Quiz.

5. The following equations describe the corrosion of iron to iron hydroxides in moist conditions.

2Fe(s) + O2(g) + 2H2O(l) 2Fe(OH)2(s)

4Fe(OH)2(s) + O2(g) + 2H2O(l) 4Fe(OH)3(s)

What substances in the equations are being oxidized?

a. Fe(s) and Fe(OH)2(s)

b. the O2(g) in both reactions

c. the O2(g) and H2O(l) in both reactions

d. Fe(OH)2(s) and Fe(OH)3(s)

END OF SHOW

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