Summary: Analytical Chemistry

Table of Contents
1. What are Redox Reactions?
2. Types of Redox Reactions
3. Oxidation and Reduction
4. Oxidizing and Reducing Agents
5. Reduction Potential
6. How to Identify Oxidizing and Reducing Agents
7. Balancing Redox Reactions
8. Oxidation-State Method
9. Ion-Electron (Half-Reaction) Method
10. Applications of Redox Reactions
11. What Happens in an Acid-Base Reaction?
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What are Redox Reactions?

• A redox reaction is a chemical change in which electrons are transferred between reactants and this is seen as a change in their oxidation states.
• Loss of electrons is called oxidation. Gain of electrons is called reduction.
• Electron-accepting species (which get reduced) are oxidizing agents. Electron-donating species (which get oxidized) are reducing agents.
• Every redox reaction can be split into two half-reactions - an oxidation half and a reduction half - and each half must account for all electrons.

Types of Redox Reactions

• Decomposition reaction - a compound breaks down into simpler substances.
• Combination reaction - two or more substances combine to form one product.
• Displacement reaction - an atom or ion in a compound is replaced by another; includes metal and non-metal displacement.
• Disproportionation reaction - a single species is both oxidized and reduced.

Oxidation and Reduction

• Oxidation: loss of electrons; can also be described as addition of oxygen, removal of hydrogen, or removal of a less electronegative element.
• Reduction: gain of electrons; can also be described as addition of hydrogen, removal of oxygen, or removal of a more electronegative element.
• Oxidation and reduction always occur together in the same chemical change.

Oxidizing and Reducing Agents

• Oxidizing agent: substance that gains electrons and is reduced.
• Reducing agent: substance that loses electrons and is oxidized.
• Some substances can act as both oxidizing and reducing agents depending on context.

Reduction Potential

• Each half-reaction has a standard electrode potential (reduction potential) measured relative to the standard hydrogen electrode.
• A more positive reduction potential means a stronger tendency to be reduced (stronger oxidizing power); a more negative value means weaker oxidizing power.

How to Identify Oxidizing and Reducing Agents

• An element in a high oxidation state in a compound is likely an oxidizing agent.
• An element in a low oxidation state in a compound is likely a reducing agent.
• If a highly electronegative element is in its highest oxidation state the compound tends to be oxidizing; in its lowest state it tends to be reducing.

Balancing Redox Reactions

• Two main methods: oxidation-state method and ion-electron (half-reaction) method. Both ensure electrons lost = electrons gained.

Oxidation-State Method

• Determine change in oxidation numbers for species undergoing oxidation and reduction.
• Use the ratio of electron changes to choose coefficients so total electrons lost = total electrons gained.
• After matching electron transfer, balance remaining atoms and charges.

Ion-Electron (Half-Reaction) Method

• Split the reaction into oxidation and reduction half-reactions.
• Balance atoms other than O and H first.
• In acidic/neutral medium balance O with H₂O and H with H⁺. In alkaline medium use H₂O and OH^-.
• Balance charges by adding electrons, multiply half-reactions so electrons cancel, then add halves and simplify.

Applications of Redox Reactions

• Generate electrical energy in batteries and electrochemical cells.
• Underlie combustion and other high-energy reactions.
• Drive biological conversions such as photosynthesis.
• Used in electrolysis, water treatment, corrosion protection (sacrificial anodes), electroplating and metal extraction.

What Happens in an Acid-Base Reaction?

• An acid-base reaction is a reaction between an acid and a base that results in neutralization; the acid donates a proton and the base accepts a proton to form conjugate species.
• Such reactions are usually carried out at room temperature and without added heat to avoid extra variables.