Question

Assign oxidation numbers to all the atoms in each of the following. a. ${\mathrm{HNO}}_3$ e. ${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6$ i. ${\mathrm{Na}}_2{\mathrm{C}}_2{\mathrm{O}}_4$ b. ${\mathrm{CuCl}}_2$ f. Ag j. ${\mathrm{CO}}_2$ c. ${\mathrm{O}}_2$ g. ${\mathrm{PbSO}}_4$ k. ${\left({\mathrm{NH}}_4\right)}_2\mathrm{Ce}{\left({\mathrm{SO}}_4\right)}_3$ d. ${\mathrm{H}}_2{\mathrm{O}}_2$ h. ${\mathrm{PbO}}_2$ 1\. ${\mathrm{Cr}}_2{\mathrm{O}}_3$

Short answer

a. H: +1, N: +5, O: -2 e. C: 0, H: +1, O: -2 i. Na: +1, C: +3, O: -2 b. Cu: +2, Cl: -1 f. Ag: 0 j. C: +4, O: -2 c. O: 0 g. Pb: +2, S: +6, O: -2 k. N: -3, H: +1, Ce: +3, S: +6, O: -2 d. H: +1, O: -1 h. Pb: +4, O: -2 1. Cr: +3, O: -2

Step-by-step solution

a. HNO3

(+1) + (x) + 3(-2) = 0 (Since the total charge of the compound is 0) x = +5 Oxidation numbers: H: +1, N: +5, O: -2

e. C6H12O6

6(x) + 12(+1) + 6(-2) = 0 x = 0 Oxidation numbers: C: 0, H: +1, O: -2

i. Na2C2O4

2(+1) + 2(x) + 4(-2) = 0 x = +3 Oxidation numbers: Na: +1, C: +3, O: -2

b. CuCl2

(x) + 2(-1) = 0 x = +2 Oxidation numbers: Cu: +2, Cl: -1

f. Ag

This is a free element, so its oxidation number is 0.

j. CO2

(x) + 2(-2) = 0 x = +4 Oxidation numbers: C: +4, O: -2

c. O2

This is a free element, so its oxidation number is 0.

g. PbSO4

(x) + (+6) + 4(-2) = 0 x = +2 Oxidation numbers: Pb: +2, S: +6, O: -2

k. (NH4)2Ce(SO4)3

2(+1) * 2 + (x) + 3(+6) + 12(-2) = 0 x = +3 Oxidation numbers: N: -3, H: +1, Ce: +3, S: +6, O: -2

d. H2O2

2(+1) + 2(-1) = 0 Oxidation numbers: H: +1, O: -1

h. PbO2

(x) + 2(-2) = 0 x = +4 Oxidation numbers: Pb: +4, O: -2

1. Cr2O3

2(x) + 3(-2) = 0 x = +3 Oxidation numbers: Cr: +3, O: -2

Key concepts

Redox Reactions

Redox reactions, short for reduction-oxidation reactions, are processes where electrons are transferred between substances. These reactions involve two simultaneous changes: oxidation, where a substance loses electrons, and reduction, where a substance gains electrons.

In a redox reaction, the substance that gives away electrons is known as the reducing agent, while the one that takes electrons is the oxidizing agent. By tracking these electron transfers, you can determine which elements are oxidized and which are reduced. This is often clarified using oxidation numbers, a key concept in balancing redox reactions and understanding electron flow.

• **Oxidation**: Increase in oxidation number
• **Reduction**: Decrease in oxidation number
• **Reducing Agent**: Donates electrons
• **Oxidizing Agent**: Accepts electrons

These reactions are significant in various applications, such as metabolism in biological systems, energy production in batteries, and many industrial processes.

Oxidation States

Oxidation states, or oxidation numbers, are useful for understanding the electron balance in chemical reactions. They indicate the degree of oxidation of an atom in a compound.

Assigning oxidation numbers helps identify the changes occurring during redox reactions and involves specific rules:

• The oxidation number of any free element is zero. Examples: O₂, Ag.
• For ions, the oxidation number equals the charge of the ion. Example: Na⁺ is +1.
• Oxygen usually has an oxidation number of -2, except in peroxides where it's -1.
• Hydrogen is generally +1, but in hydrides, it's -1.

By following these rules, one can calculate the oxidation state of each element in a compound, helping to determine the nature of redox reactions.

Chemical Compounds

Chemical compounds are substances composed of two or more different elements bonded together. The properties of each compound are determined by the types and ratios of atoms involved.

To better understand the distribution of electrons in compounds, oxidation numbers are employed, revealing how electrons are shared or transferred among elements. For example:

• **HNO₃**: This compound has nitrogen with an oxidation state of +5.
• **C₆H₁₂O₆**: Carbon in this organic compound has a balanced oxidation state of 0.
• **Na₂C₂O₄**: Carbon here carries an oxidation state of +3.

Understanding these properties is essential in predicting the behavior of compounds during chemical reactions. Each compound's unique oxidation state configuration allows for the interpretation of their reactivity and function in various chemical processes.