4B4 Oxidation and Reduction Flashcards
Describe components of oxidation and reduction reactions.
Define:
oxidation number
The charge an atom would have if the compound was made up of ions.
Oxidation numbers indicate the degree of oxidation or reduction of an atom.
What is the oxidation number of a free element?
Zero
Free elements like oxygen, nitrogen, and sulphur have an oxidation number of zero.
Fill in the blank:
The sum of oxidation numbers in a neutral compound is _____.
Zero
The sum equals the net charge of the compound.
Which rule determines the oxidation number of Group IA elements?
Group IA elements always have an oxidation number of +1.
This rule applies unless combined with a more electronegative element.
List three uses of oxidation numbers.
- Naming compounds.
- Balancing equations.
- Determining valency.
Oxidation numbers are critical in redox chemistry.
How are oxidation numbers calculated in a binary ionic compound?
- Identify the elements in the compound.
- Identify their charge by looking at the periodic table.
- Pay attention to the ratio of elements.
- Solve for any unknown charges.
For example, the compound FeCl₃ is contains 3 chlorine, each with a charge of -1 for a total value of -3. Therefore, the iron (Fe) must equal to +3 since there is no overall charge on this compound.
Calculate the oxidation number of chlorine in ClO₃⁻.
5
Cl + 3 (-2) = −1
Solving gives Cl = +5
True or False:
The oxidation number of a monatomic ion equals the charge of the ion.
True
For example, Na⁺ has an oxidation number of +1 and S²⁻ has an oxidation number of -2.
What is the oxidation number of fluorine in compounds?
-1
Fluorine is always -1 because it is the most electronegative element.
Define:
redox reaction
A reaction involving the transfer of electrons where one species is oxidized and another is reduced.
Oxidation and reduction always occur together in redox reactions.
What is an oxidizing agent?
A compound that easily gains electrons, decreases its oxidation state, and gets reduced.
Oxidizing agents accept electrons, becoming more negative, and are reduced in the process.
What is a reducing agent?
A compound that easily loses electrons, increases its oxidation state, and gets oxidized.
Reducing agents donate electrons, becoming more positive, and are oxidized in the process.
How can you identify an oxidizing agent in a reaction?
Look for a compound whose oxidation state decreases during the reaction.
Oxidizing agents lower their oxidation state as they gain electrons.
True or False:
Hydrogen gas can act as both an oxidizing and a reducing agent.
True
The role of hydrogen gas depends on the context of the reaction.
Which element is oxidized in the reaction Zn → Zn²⁺ + 2e⁻?
Zinc
(Zn)
Zinc’s oxidation number increases from 0 to +2.
Which element is reduced in the reaction 2Fe³⁺ + 3Mg → 2Fe⁺ + 3Mg²⁺?
Iron
(Fe)
Fe³⁺ is reduced to Fe by gaining electrons; Its oxidation number decreases from 3 to o.
Which element acts as the oxidizing agent in the reaction: Fe²⁺ + Se⁴⁺ → Fe³⁺ + Se³⁺?
Selenium
(Se⁴⁺)
Selenium’s oxidation state decreases from +4 to +3, making it the oxidizing agent.
How can half-reactions be used to represent redox processes?
By isolating either oxidation or reduction processes in a reaction.
Half-reactions focus on either electron gain (reduction) or electron loss (oxidation) without showing the full reaction.
List two ways to recognize a redox reaction.
- Changes in oxidation states.
- Simultaneous occurrence of reduction and oxidation.
Redox reactions are identified by analyzing the oxidation state changes of reactants and products.
Fill in the blank:
During a displacement reaction, the element that is displaced is _______.
reduced
In displacement reactions, the displaced element gains electrons and is reduced.
Fill in the blank:
Combustion reactions use _______ to oxidize organic compounds.
oxygen
Combustion reactions involve oxygen as the oxidizing agent to break down organic compounds.
What is electrochemistry?
The study of the transformation of chemical energy into electrical energy and vice versa.
Electrochemistry involves redox reactions and is vital for technologies like batteries and fuel cells.
Define:
an electrochemical cell
A device that converts chemical energy into electrical energy through a redox reaction.
Electrochemical cells are the basis of batteries and involve electron flow through a circuit.
What are the two main parts of an electrochemical cell?
- Electrodes
- An electrolyte
Electrodes are conductors where reactions occur, and the electrolyte conducts ions.
Which electrode is positive in an electrochemical cell?
The cathode.
The cathode is where reduction occurs, and electrons are gained.
Fill in the blank:
The ______ is the negative electrode where oxidation occurs.
anode
The anode loses electrons and is the source of electron flow in the circuit.
What is the function of the electrolyte in an electrochemical cell?
- To conduct ions.
- To prevent charge buildup on the electrodes.
The electrolyte completes the internal circuit by allowing ion flow between compartments.
How are electrons transferred in an electrochemical cell?
From the anode to the cathode through a wire.
Electrons flow from the anode (oxidation site) to the cathode (reduction site).
Electrons flow due to the redox reaction, generating an electrical current.
List two materials commonly used as electrodes in electrochemical cells.
- Zinc (anode)
- Copper (cathode)
These metals are common due to their distinct electrochemical properties.
Which component prevents charge buildup in the electrolyte solutions?
The salt bridge or porous barrier.
It allows ions to move between compartments to balance the charge.
Fill in the blank:
A lemon in a homemade battery acts as the ________.
electrolyte
The lemon juice contains ions that conduct electricity.
What are the electrodes in a homemade lemon battery?
A copper penny (cathode) and a galvanized nail (anode).
These electrodes are connected by a wire to complete the circuit.
What happens if the electrodes in a lemon battery touch?
The circuit short-circuits, and no useful current is produced.
Proper separation is essential for the battery to function.
How can you increase the voltage of a homemade lemon battery?
Connect multiple lemons in series.
Connecting lemons in series adds their voltages together.
Connecting cells in series combines their voltages to power devices requiring more energy.
What are the two types of electrochemical cells?
- Galvanic (Voltaic) cells
- Electrolytic cells
Galvanic cells generate electricity through a spontaneous redox reaction, while electrolytic cells use external energy to drive reactions.
Which electrode is negatively charged in a Galvanic cell?
The anode.
In Galvanic cells, the anode is negative because it releases electrons.
Which electrode is positively charged in an electrolytic cell?
The anode.
In electrolytic cells, the anode is positive because it attracts anions.
What is cell notation, and how is it used?
A shorthand to represent the reactions in an electrochemical cell, with the anode on the left and cathode on the right.
For example, Zn(s) | Zn²⁺ (aq) || Cu²⁺ (aq) | Cu(s) represents the half-reactions of Zinc and Copper.
What is the relationship between E°cell, E°cathode, and E°anode?
E°cell = E°cathode − E°anode
The electrochemical potential of the cell is the difference in reduction potentials of the cathode and anode.
Reduction potentials can be found in standard tables, and the anode potential must be reversed for oxidation.
How do the charges of the anode and cathode differ in Galvanic and electrolytic cells?
- Galvanic cells: The anode is negative and the cathode is positive.
- Electrolytic cells: The anode is positive and the cathode is negative.
The roles are reversed because of the nature of the energy source driving the reactions.
What is the general equation for the anode reaction?
X(s) → X⁺(aq) + e⁻
This represents the loss of electrons during oxidation.
What is the general equation for the cathode reaction?
Y⁺(aq) + e⁻ → Y(s)
This represents the gain of electrons during reduction.
