Oxidation Numbers

1. In chemistry, any element in the free state (not combined with another element) has an oxidation number of ___?

0

2

1

-1

In the free state, the oxidation number of an element is always 0 because there is no transfer of electrons involved.

Explanation

In the free state, the oxidation number of an element is always 0 because there is no transfer of electrons involved.

2. The oxidation number of any monatomic ion equals ________________.

Half of the charge of the ion.

Double the charge of the ion.

The charge of the ion

The atomic number of the ion.

The oxidation number of a monatomic ion is determined by the charge of the ion itself, which indicates the number of electrons gained or lost. It is directly correlated with the charge and not impacted by other factors like half or double the charge, or the atomic number.

Explanation

The oxidation number of a monatomic ion is determined by the charge of the ion itself, which indicates the number of electrons gained or lost. It is directly correlated with the charge and not impacted by other factors like half or double the charge, or the atomic number.

3. Oxygen in compounds is assigned an oxidation number of ___, except in peroxides in which it has an oxidation number of ___.

1+, 2-

0, 2+

2- 1-

-2, 1+

In most compounds, oxygen has an oxidation number of 2-, but in peroxides, it has an oxidation number of 1-. This is due to the nature of the peroxide ion and its unique structure.

Explanation

In most compounds, oxygen has an oxidation number of 2-, but in peroxides, it has an oxidation number of 1-. This is due to the nature of the peroxide ion and its unique structure.

4. Hydrogen in compounds has an oxidation number of ___, except in metal hydrides in which it has an oxidation number of ___.

2+ 2-

0 0

1+ 1-

3- 3+

In compounds, hydrogen typically has an oxidation number of 1+. However, in metal hydrides, hydrogen has an oxidation number of 1-. The other options provided are incorrect oxidation numbers for hydrogen in compounds and metal hydrides.

Explanation

In compounds, hydrogen typically has an oxidation number of 1+. However, in metal hydrides, hydrogen has an oxidation number of 1-. The other options provided are incorrect oxidation numbers for hydrogen in compounds and metal hydrides.

5. Group 1A (alkali metals) elements always have an oxidation number of ___ in compounds.

2+

0

3-

1+

In compounds, Group 1A elements (alkali metals) tend to lose one electron, resulting in an oxidation number of 1+. Options 2+, 3-, and 0 do not accurately reflect the common oxidation state of alkali metals.

Explanation

In compounds, Group 1A elements (alkali metals) tend to lose one electron, resulting in an oxidation number of 1+. Options 2+, 3-, and 0 do not accurately reflect the common oxidation state of alkali metals.

6. Group 2A (alkali earth metals) elements always have an oxidation number of ___ in compounds.

1+

0

2+

3-

Group 2A elements, also known as alkali earth metals, typically lose two electrons to achieve a stable electron configuration, hence the oxidation number of 2+ in compounds. Option 1+ is incorrect because they must lose two electrons, not just one. Option 3- is incorrect as these elements are typically cations, not anions. Option 0 is incorrect as these elements do not gain electrons to have a 0 oxidation number.

Explanation

Group 2A elements, also known as alkali earth metals, typically lose two electrons to achieve a stable electron configuration, hence the oxidation number of 2+ in compounds. Option 1+ is incorrect because they must lose two electrons, not just one. Option 3- is incorrect as these elements are typically cations, not anions. Option 0 is incorrect as these elements do not gain electrons to have a 0 oxidation number.

7. Boron and aluminum always have an oxidation number of ___ in compounds.

3+

2+

1-

5+

Boron and aluminum commonly exhibit an oxidation number of 3+ in compounds due to their electron configuration and chemical properties.

Explanation

Boron and aluminum commonly exhibit an oxidation number of 3+ in compounds due to their electron configuration and chemical properties.

8. In binary compounds with metals the nonmetallic elements of group 6A (chalcogens) generally have an oxidation number of ___?

2-

-1

0

-2

In binary compounds with metals, nonmetallic elements of group 6A (chalcogens) usually gain two electrons to achieve a stable electron configuration, resulting in an oxidation number of 2-.

Explanation

In binary compounds with metals, nonmetallic elements of group 6A (chalcogens) usually gain two electrons to achieve a stable electron configuration, resulting in an oxidation number of 2-.

9. In binary compounds with metals, what is the oxidation number of the elements of group 7A (halogens)?

-1

1+

1-

7-

In binary compounds with metals, the elements of group 7A (halogens) typically have an oxidation number of -1, indicating that they gain one electron during chemical reactions. This is due to their high electronegativity and tendency to form ionic bonds with metals.

Explanation

In binary compounds with metals, the elements of group 7A (halogens) typically have an oxidation number of -1, indicating that they gain one electron during chemical reactions. This is due to their high electronegativity and tendency to form ionic bonds with metals.

10. The charge of a polyatomic ion is considered its ___ oxidation number. Example: SO42-

Total

Net, SO42- has a net oxidation number of 2-

Covalent

Average

The oxidation number of a polyatomic ion is determined by the net charge on the ion, hence it is referred to as the net oxidation number.

Explanation

The oxidation number of a polyatomic ion is determined by the net charge on the ion, hence it is referred to as the net oxidation number.

11. In assigning oxidation numbers in a compound, the elements closest to which element in the periodic table are always assigned the negative oxidation number? Example: P4O10.

Sodium

Fluorine, In P4O10 oxygen has the negative oxidation number of 2-

Argon

Hydrogen

In compounds, oxygen is typically assigned negative oxidation numbers when paired with more electronegative elements. Fluorine, being the most electronegative element, results in the most negative oxidation numbers.

Explanation

In compounds, oxygen is typically assigned negative oxidation numbers when paired with more electronegative elements. Fluorine, being the most electronegative element, results in the most negative oxidation numbers.

12. For neutral compounds, the sum of the oxidation numbers of all atoms in the compound must equal ___ . Example: Na2S.

1

-1

0, Na2 (2 x 1+) + S (2-) = 0

2

In a neutral compound, the sum of the oxidation numbers of all atoms must always add up to 0 due to the conservation of charge. In the example Na2S, the oxidation number of Na (Group 1 element) is +1, and the oxidation number of S (Group 16 element) is -2. When you add them up, you get 2(+1) + (-2) = 0.

Explanation

In a neutral compound, the sum of the oxidation numbers of all atoms must always add up to 0 due to the conservation of charge. In the example Na2S, the oxidation number of Na (Group 1 element) is +1, and the oxidation number of S (Group 16 element) is -2. When you add them up, you get 2(+1) + (-2) = 0.

13. For polyatomic ions the sum of the oxidation numbers of the elements must equal _______________. Example: CO32-.

The number of elements in the ion

The charge of the ion, O3 (3 x 2-) + C (must be 4+) = 2-

The atomic number of the element with the highest oxidation number

Zero

The sum of oxidation numbers in a polyatomic ion must equal the charge of the ion to maintain electrical neutrality.

Explanation

The sum of oxidation numbers in a polyatomic ion must equal the charge of the ion to maintain electrical neutrality.