22.4.1 Oxygen

Question 1

Oxygen

Answer 1

• Oxygen comprises only 21% of air, but accounts for 49.5% of the earth’s crust.
• Stratospheric ozone (O 3 ) absorbs ultraviolet radiation, while ground-level ozone is damaging.
• Most nonmetal oxides are acidic in water, while most metal oxides are basic in water. Amphoteric oxides can react with acids and bases.
• A peroxide is a compound that contains oxygen in the 1– oxidation state.

Question 2

note 1

Answer 2

• Oxygen accounts for only 21% of air. Pure elemental oxygen can be obtained by cooling air to 77 K, then slowly warming the air to distill the various components. Oxygen is a paramagnetic molecule. If liquid oxygen is poured between two magnets, it will be attracted to the magnets.
• Oxygen comprises about 49.5% of the Earth’s crust by mass as oxides, carbonates, and silicates.
• Stratospheric ozone extends from 19 to 48 kilometers in the atmosphere. Although the concentration is low (only 10 parts per million), it serves a critical function of absorbing ultraviolet radiation.
• While stratospheric ozone protects life on earth, ground-level ozone is damaging. Ozone can cause aging of skin, and is a component of smog.

Question 3

note 2

Answer 3

• Most nonmetal oxides are acidic in water. For example,
  carbon dioxide reacts with water to form carbonic acid.
  Similarly, sulfur trioxide reacts with water to form sulfuric
  acid. However, neither carbon monoxide nor dinitrogen
  monoxide form acidic compounds in water.
• Most metal oxides are acidic in water. For example, sodium oxide reacts with water to form sodium hydroxide. While iron(III) oxide does not dissolve in water, it functions as a base in the presence of an acid, forming water and iron(III) ion.
• Oxides formed from elements near the border between metals and nonmetals are often amphoteric oxides, which can react with acids and bases. For example, aluminum oxide acts as an acid in basic solution, but as a base in acidic solution.
• A peroxide is a compound that contains oxygen in the 1– oxidation state.
• Benzoyl peroxide oxidizes and kills bacteria on the surface of the skin.
• Hydrogen peroxide can be used as a bleach. Both sodium perborate and sodium percarbonate work by providing hydrogen peroxide contained in a solid lattice. When these compounds are added to water, they release the hydrogen peroxide.
• Hydrogen peroxide is used to treat cuts. It foams on wounds because of the enzyme catalase, which catalyzes the disproportionation of hydrogen peroxide. In a disproportionation reaction, the same reactant serves as both an oxidizing agent and a reducing agent. Hydrogen peroxide acts as an oxidizing agent, accepting electrons to form water. Hydrogen peroxide also acts as a reducing agent, losing electrons to form oxygen gas.

Question 4

Which chemical structure does not correspond to the name given?

Answer 4

Sulfur trioxide

Question 5

If ozone is so beneficial in the stratosphere, why is an ozonating air purifier not the best choice for cleaning household air?

Answer 5

Ozone is an irritant to the eyes and lungs, and can accelerate aging

Question 6

Arrange the following binary oxides in order of increasing covalent character:

Oxides: SO2, MgO, PbO2, and F2O

Answer 6

MgO < PbO2 < SO2 < F2O

Question 7

The ability to possess either positive or negative oxidation states is a common characteristic of what?

Answer 7

Nonmetals

Question 8

Which of the following is not an application of oxygen compounds?

Answer 8

Oxidation of metal oxides in ores

Question 9

Which of the following compounds is an amphoteric oxide?

Answer 9

Al2O3

Question 10

For the following oxides, oxidation states (or oxidation numbers) have been assigned to all atoms. Which choice shows INCORRECT oxidation states for the given oxide?

Answer 10

Cl2O7 Cl is +5 O is −2

Question 11

Carbon, nitrogen, oxygen, and fluorine are all nonmetals that can form homonuclear diatomic X2 molecules, yet only C, N and O form multiple bonds. It is also interesting that of the C, N, O, and F diatomic molecules, only O2 is paramagnetic; the rest are diamagnetic. Why are O2 molecules paramagnetic?

Answer 11

Oxygen contains unpaired electrons.

Question 12

Which of these types of minerals does not contain oxygen?

Answer 12

Halides

Question 13

Oxygen typically reacts with nonmetals to form oxides that are acidic in water. Which of the following nonmetal oxides does not act as an acid in water?

Answer 13

N2O