In each of these reactions assign oxidation numbers to all...

In each of these reactions assign oxidation numbers to all species, and tell which substance is oxidized and which is reduced. Tell which is the oxidizing agent and which is the reducing agent. (a) $\mathrm{Fe}(\mathrm{s})+\mathrm{Br}_{2}(\ell) \longrightarrow \mathrm{FeBr}_{2}(\mathrm{~s})$ (b) $8 \mathrm{HI}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \stackrel{\longrightarrow}$ $\mathrm{H}_{2} \mathrm{~S}(\mathrm{aq})+4 \mathrm{I}_{2}(\mathrm{~s})+4 \mathrm{H}_{2} \mathrm{O}(\ell)$ (c) $\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq})+2 \mathrm{Fe}^{2+}(\mathrm{aq})+2 \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq}) \stackrel{2}{2 \mathrm{Fe}^{3+}(\mathrm{aq})}+4 \mathrm{H}_{2} \mathrm{O}(\ell)$

In each of these reactions assign oxidation numbers to all species, and tell which substance is oxidized and which is reduced. Tell which is the oxidizing agent and which is the reducing agent.
(a) $\mathrm{Fe}(\mathrm{s})+\mathrm{Br}_{2}(\ell) \longrightarrow \mathrm{FeBr}_{2}(\mathrm{~s})$
(b) $8 \mathrm{HI}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{SO}_{4}(\mathrm{aq}) \stackrel{\longrightarrow}$
$\mathrm{H}_{2} \mathrm{~S}(\mathrm{aq})+4 \mathrm{I}_{2}(\mathrm{~s})+4 \mathrm{H}_{2} \mathrm{O}(\ell)$
(c) $\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{aq})+2 \mathrm{Fe}^{2+}(\mathrm{aq})+2 \mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq}) \stackrel{2}{2 \mathrm{Fe}^{3+}(\mathrm{aq})}+4 \mathrm{H}_{2} \mathrm{O}(\ell)$

Key Concepts

Reduction

Reduction is the gain of electrons by a species, resulting in a decrease in its oxidation number. This process involves an increase in electron density and is crucial for balancing redox reactions, as it pairs with the oxidation process.

Reducing Agent

A reducing agent is a substance that causes another species to be reduced by donating electrons. As it loses electrons, the reducing agent undergoes oxidation, and its oxidation number increases. This concept is essential when analyzing the flow of electrons in redox reactions.

Oxidizing Agent

An oxidizing agent is a substance that facilitates oxidation by accepting electrons from another species. In the process, the oxidizing agent itself is reduced, which means its oxidation number decreases as it gains electrons.

Oxidation

Oxidation is defined as the process in which a species loses electrons, leading to an increase in its oxidation number. This change reflects the atom’s or ion’s decrease in electron density and is a fundamental concept in understanding electron transfer reactions.

Oxidation Numbers

Oxidation numbers are numerical values assigned to atoms in a compound or ion that help in tracking the electron transfer processes in redox reactions. They provide a systematic way to determine which atoms have undergone oxidation (increase in oxidation number) and which have undergone reduction (decrease in oxidation number). These values are assigned based on a set of rules that consider electronegativity, molecular structure, and known oxidation states of common elements.

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