2.1.5 Redox

Question 1

What is an oxidation number?

Answer 1

The number of electrons an atom uses to bond with any other atom

Question 2

What is the oxidation number of an uncombined element such as C, H, O₂?

Answer 2

0, because it is an uncombined element

Question 3

What is the oxidation number of combined oxygen such as in H₂O?

Answer 3

-2

Question 4

What is the oxidation number of oxygen in peroxides?

Answer 4

-1

Question 5

What is the oxidation number of combined hydrogen such as in NH₃ or H₂S?

Answer 5

1

Question 6

What is the oxidation number of hydrogen in metal hydrides such as LiH?

Answer 6

-1

Question 7

What is the oxidation number of a simple ion?

Answer 7

Charge on the ion. E.g., Na⁺ → +1; Cl⁻ → -1

Question 8

What is the oxidation number of combined fluorine such as in NaF, CaF₂?

Answer 8

-1

Question 9

When an element has more than one stable oxidation number, how is it indicated?

Answer 9

It is written as a Roman numeral

Question 10

What is the oxidation number of Fe in iron (III) chloride?

Answer 10

3

Question 11

What are oxyanions?

Answer 11

Negative ions that have an element along with oxygen

Question 12

What is the oxidation number of S in SO₄²⁻?

Answer 12

+6. Explanation: Combined oxygen has an oxidation number of -2. Calculation: 4 × -2 = -8. Compound charge: -2. Sum of oxidation numbers must equal -2. So, -2 - (-8) = +6

Question 13

Define oxidation in terms of electron transfer and oxidation number.

Answer 13

Oxidation is: • Loss of electrons • An increase in oxidation number

Question 14

Define reduction in terms of electron transfer and oxidation number.

Answer 14

Reduction is: • Gain of electrons • A decrease in oxidation number

Question 15

What is a redox reaction?

Answer 15

A reaction in which both oxidation and reduction take place

Question 16

What is the oxidation number of a metal?

Answer 16

0, because it is an uncombined element