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Questions and Answers
In a redox reaction, the substance that loses electrons is called the ______.
In a redox reaction, the substance that loses electrons is called the ______.
reducing agent
Oxidation always occurs at the ______.
Oxidation always occurs at the ______.
anode
The ______ is the electrode where reduction occurs in an electrochemical cell.
The ______ is the electrode where reduction occurs in an electrochemical cell.
cathode
Reduction occurs at the ______.
Reduction occurs at the ______.
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In a voltaic cell, chemical energy is converted into ______ energy.
In a voltaic cell, chemical energy is converted into ______ energy.
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In a voltaic cell, the flow of electrons is from the ______ to the cathode.
In a voltaic cell, the flow of electrons is from the ______ to the cathode.
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The electrode where oxidation takes place is called the ______.
The electrode where oxidation takes place is called the ______.
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The salt bridge allows for the flow of ______ ions between half-cells.
The salt bridge allows for the flow of ______ ions between half-cells.
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The build-up of hydrogen bubbles on the anode can increase the ______ of the cell.
The build-up of hydrogen bubbles on the anode can increase the ______ of the cell.
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Primary cells are also known as ______ cells.
Primary cells are also known as ______ cells.
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Secondary batteries can reverse the chemical reaction that generates ______ by applying an electric current.
Secondary batteries can reverse the chemical reaction that generates ______ by applying an electric current.
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In an electrolytic cell, electrical energy is converted into ______ energy.
In an electrolytic cell, electrical energy is converted into ______ energy.
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In a primary cell, the reactions are ______ and cannot be reversed once all materials are used.
In a primary cell, the reactions are ______ and cannot be reversed once all materials are used.
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Reactive metals from group 1 and 2 can act as ______ agents in redox reactions.
Reactive metals from group 1 and 2 can act as ______ agents in redox reactions.
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The electrochemical cell that allows reactions to be reversed is called a ______ cell.
The electrochemical cell that allows reactions to be reversed is called a ______ cell.
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The reaction in a lead-acid battery is a type of ______ reaction.
The reaction in a lead-acid battery is a type of ______ reaction.
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Electrolytic cells convert electrical energy into chemical energy through a process called ______.
Electrolytic cells convert electrical energy into chemical energy through a process called ______.
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In an electrolytic cell, electrons flow from the negative terminal to the ______.
In an electrolytic cell, electrons flow from the negative terminal to the ______.
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The electrode that undergoes reduction in an electrolytic cell is called the ______.
The electrode that undergoes reduction in an electrolytic cell is called the ______.
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A standard hydrogen electrode (SHE) has a potential defined as ______.
A standard hydrogen electrode (SHE) has a potential defined as ______.
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In voltaic cells, the flow of electrons occurs from the ______ to the cathode.
In voltaic cells, the flow of electrons occurs from the ______ to the cathode.
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The ease of oxidation and reduction of a species is measured by its standard ______ potential.
The ease of oxidation and reduction of a species is measured by its standard ______ potential.
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The electrolyte in an electrolytic cell contains free-moving ______ and anions.
The electrolyte in an electrolytic cell contains free-moving ______ and anions.
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In the reactivity series, species more negative than hydrogen will have a greater ease in ______.
In the reactivity series, species more negative than hydrogen will have a greater ease in ______.
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Study Notes
Oxidation and Reduction
- Oxidation and reduction can be defined in several ways, including by oxygen gain/loss, hydrogen loss/gain, or electron transfer.
- Oxidation is the combination of a substance with oxygen.
- Reduction is the removal of oxygen from a substance.
- Oxidation is the loss of electrons.
- Reduction is the gain of electrons.
- The oxidation state represents the charge an atom would have if the compound were composed of ions.
- If a compound is oxidized, its oxidation state increases. This causes another species to reduce, making it a reducing agent.
- If a compound is reduced, its oxidation state decreases. This causes another species to oxidize, making it an oxidizing agent.
Half-equations
- Redox reactions can be separated into oxidation and reduction half-equations.
- This helps balance redox reactions.
- Steps for balancing redox reactions:
- Identify oxidized and reduced species.
- Separate into oxidation and reduction half-equations.
- Balance the equations, ensuring the number of electrons is equal.
- Add balanced half-equations and cancel electrons.
- In acidic solutions, add H₂O to balance oxygen and H⁺ to balance hydrogen.
- In neutral or basic solutions, add OH⁻ to balance oxygen and H₂O to balance hydrogen.
- Example: 2Na + Cl₂ → 2NaCl. The half-equations are Na → Na⁺ + e⁻ and Cl₂ + 2e⁻ → 2Cl⁻.
Relative Ease of Oxidation/Reduction
- Halogens can act as oxidizing agents. Reactivity increases going up the group
- Group 1 metals can act as reducing agents. Reactivity increases going down the group.
Redox reactions of acids and metals
- Reactive metals, such as those in Groups 1 and 2, readily oxidize with strong acids, producing a salt and hydrogen gas.
Electrochemical Cells
- Electrochemical cells interconvert electrical and chemical energy.
- Types of electrochemical cells include primary (voltaic), secondary (rechargeable), and fuel cells.
- Chemical energy is converted to electrical energy in these cells.
Electrolytic Cells
- Electrolytic cells convert electrical energy into chemical energy.
- Oxidation and reduction are not spontaneous in these cells and require an external electrical source. (electrolysis)
- Electrolytic cells consist of a single container filled with an electrolyte (ionic salt solution) and electrodes placed within the electrolyte.
- A DC electric current is applied to the electrodes.
Case Studies
- Lead-acid batteries: These batteries utilize a chemical reaction involving lead, lead(IV) oxide, and sulfuric acid. The reaction releases energy on discharge and can be reversed (recharged) using electricity.
- Lithium-ion batteries: These batteries include lithium atoms embedded in a graphite electrode and a lithium-cobalt oxide cathode. They utilize a reversible chemical reaction that can be recharged.
Fuel Cells
- Fuel cells convert chemical energy (fuel and oxygen) directly into electrical energy and water.
- Various fuels like hydrogen, methanol, and ethanol are used.
Oxidation and Reduction of Organic Compounds
- Various reactions involving organic components.
Standard Electrode Potentials
- It defines the ease of oxidation/reduction of substances under standard conditions.
- A standard hydrogen electrode (SHE) has a potential of 0V.
- Species with more negative reduction potentials are more easily oxidized.
- Standard cell potential (E°cell) equals the potential of the cathode minus the potential of the anode.
- A positive E°cell indicates a spontaneous reaction.
Gibbs Energy and Standard Cell Potential
- Gibbs free energy change (∆G°) is related to the standard cell potential through the equation ∆G° = -nFE°cell (where n is the number of electrons transferred and F is Faraday's constant.)
- Positive E°cell leads to negative ∆G°, a spontaneous reaction.
Electrolysis of Aqueous Solutions
- Electrolysis involves a non-spontaneous redox reaction powered by an external electrical power source.
- In aqueous solutions, water itself can be oxidized or reduced depending on the potential of the cation/anion.
- Water may be the species oxidized or reduced ahead of the ion involved. Oxidation/reduction of water will take place at the electrode.
Electroplating
- Electroplating is a process where material is transferred from one electrode (anode) to another (cathode) by electrolysis.
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Description
Test your understanding of oxidation and reduction in chemistry. This quiz covers definitions, characteristics, and the balancing of redox reactions through half-equations. Challenge yourself to demonstrate your knowledge of these fundamental concepts.
