Grade 11 Chemistry - Chapter 4
Demonstration: Zinc Rod in Copper(II) Solution
In this experiment, a zinc rod is placed in an aqueous copper(II) solution. This setup demonstrates a displacement reaction.
Demonstration: Copper Strip in Zinc Solution
Similar to the previous demonstration, this experiment involves placing a copper strip in an aqueous zinc solution.
Displacement Reactions of Halogens and Halides
Displacement reactions involving halogens and halides are intriguing chemical processes.
Equations of the Displacement Reactions of Halogens
The equations for displacement reactions of halogens can be represented as follows:
Half Reaction
A half reaction is a chemical reaction that shows the gain or loss of electrons.
Oxidation
Oxidation is a half reaction in which electrons are lost, often accompanied by the gain of oxygen.
Reduction
Reduction is a half reaction in which electrons are gained, or there is a loss of oxygen.
An Oxidation-Reduction Reaction
An oxidation-reduction reaction, also known as a redox reaction, is the combination of two half reactions—oxidation and reduction.
Reducing Agent
A reducing agent is a species that undergoes oxidation, causing another substance to be reduced.
Oxidizing Agent
An oxidizing agent is a species that undergoes reduction, causing another substance to be oxidized.
Drawing an Electrochemical Cell
An electrochemical cell can be depicted by illustrating its key components, including two half cells, a salt bridge, metal rods, and connections with wires and a voltmeter.
Components of an Electrochemical Cell
An electrochemical cell consists of two half cells, each containing a metal rod immersed in its solution. The two half cells are internally connected by a salt bridge and externally connected by metal wires and a voltmeter.
Salt Bridge
A salt bridge is a glass tube containing an aqueous soluble electrolyte that does not interfere with the reaction.
Anode
The anode is the electrode at which oxidation occurs. It is the negative terminal of the cell.
Cathode
The cathode is the electrode at which reduction occurs. It is the positive terminal of the cell.
Electron Flow
Electrons flow in the wires from the anode to the cathode.
Current Flow
Current flows in the wires from the cathode to the anode.
Ions Flow in the Salt Bridge
Ions flow in the salt bridge to maintain electrical neutrality. Cations (positive ions) travel towards the cathode, while anions (negative ions) move towards the anode.
Voltage Drop in an Electrochemical Cell
In an electrochemical cell, the voltage eventually drops to zero after a long time, especially if the reactions reach equilibrium.
Cu-Ag Cell Reactions
In a copper-silver (Cu-Ag) cell, specific reactions occur at the anode and cathode.
Performing Calculations with Electrochemical Cells
Electrochemical cells allow for various calculations involving voltage, current, and energy changes.
Grade 11 Chemistry - Chapter 4
Cu-Ag Cell Reactions
In a copper-silver (Cu-Ag) cell, specific reactions occur at the anode and cathode.
🟣 Anode Reaction: The anode typically involves the oxidation of copper (Cu) metal.
🟠 Cathode Reaction: The cathode often involves the reduction of silver (Ag) ions.
Performing Calculations with Electrochemical Cells
Electrochemical cells allow for various calculations involving voltage, current, and energy changes.
📈 Mathematics: These calculations help understand the energy transformations in redox reactions and can be essential in practical applications.
Redox Reactions Identification
Redox reactions can be identified by specific characteristics, one of which is an increase in the number of oxygen atoms.
⚖️ Oxidation Number: Analyzing changes in oxidation numbers can aid in recognizing redox reactions.
Predicting Spontaneous Reactions
Spontaneous reactions can be predicted by using a list of equations arranged in decreasing tendency to lose electrons.
🧪 Trends: Understanding the reactivity trends of substances can help identify spontaneous reactions.
Using a Voltmeter for Measurement
A voltmeter is used to measure the energy released by a cell, represented by the product of charge (Q) and voltage (V).
📝 Equation: The equation W = Q × V relates the work done (energy) to the charge and voltage.
Standard Hydrogen Electrode (SHE)
A standard hydrogen electrode is a reference electrode consisting of a rod of mossy platinum with gaseous hydrogen being bubbled onto it. It is immersed in a 1M acid solution.
🌡️ Standard Conditions: SHE is used as a reference under specific standard conditions for electrochemical measurements.
Standard Conditions
Standard conditions for electrochemical measurements ensure consistency. These conditions include:
- All aqueous solutions having a concentration of 1.0M.
- All gases having a pressure of 1.00 atm.
- A temperature of 25°C.
Standard Electromotive Force (E°net)
Standard electromotive force of a cell, E°net, represents the energy released throughout the circuit when a coulomb of electrons passes through any one point in the main circuit.
⚡ Definition: It is the voltage of the cell when each electrode is placed in 1M solution of its ions, at 25°C, and 1 atmosphere.
Representation of Electrochemical Cells
An electrochemical cell can be represented using line notation, which simplifies the description of the cell's components and reactions.
📏 Clarity: Line notation makes it easy to convey complex electrochemical setups concisely.
E°net for Combined Reactions
If a reaction is the sum of two other reactions, then its E°net is the sum of their E°net values.
📏 Mathematics: This principle helps determine the overall E°net for complex redox reactions.
Standard Half-Cell Potential (E°)
The standard half-cell potential, denoted as E°, represents the electromotive force E° of the cell formed between this half cell and a standard hydrogen half cell.
📏 Reference: E° values are essential for calculating cell potentials and predicting the spontaneity of reactions.
Predicting Effects on E° of the Cell
The effect of a change on E° of the cell can be predicted using Le Chatelier's principle (LCP).
⚖️ Shift in Equilibrium: LCP helps anticipate how changes in concentration, temperature, or pressure affect E° values.
E°cell Calculation
E°cell is calculated by adding the E° values for the oxidation and reduction half-reactions.
📏 Summation: This calculation provides the overall cell potential and indicates the spontaneity of the cell reaction.
Spontaneity of Reactions
If E°cell is greater than 0, the reaction is spontaneous. If E°cell is less than 0, the reverse reaction is spontaneous. If E°cell equals 0, the reaction is at equilibrium.
⚡ Energetic Considerations: E°cell values offer insights into the spontaneity of redox reactions.
E°net and Reaction Rates
While E°net allows us to predict the spontaneity of reactions, it does not provide information about their rates of reaction.
🕒 Kinetics: Reaction rates depend on factors such as activation energy and concentration.
Factors Preventing Reactions
Sometimes, even if E°net of a cell is greater than 0, reactions may not take place due to:
- High activation energy requirements.
- Non-standard conditions affecting reaction feasibility.
Grade 11 Chemistry - Chapter 4
Electrolysis
Electrolysis is the process whereby an electric current is used to force a non-spontaneous reaction to take place.
⚡ Anode and Cathode: In electrolysis, the anode is the positive terminal at which oxidation takes place, and the cathode is the negative terminal at which reduction takes place.
Electrolysis of Molten Salts
In electrolysis of a molten salt, the metal is produced at the cathode, and the non-metallic element at the anode.
🧪 Examples: Many metals such as sodium, calcium, and aluminum are extracted from their ores by electrolysis of their molten salts.
Identifying Products of Electrolysis
Identify the products of the electrolysis of molten and aqueous salts.
🧪 Analysis: The products depend on the specific salt and conditions of electrolysis.
Electroplating
Electroplating is the process of using electricity to cover an object with a thin layer of metal.
🧪 Electrodes: In electroplating, Cu/Ag are called reacting electrodes, and C/Pt are considered inert electrodes.
Applying Electrolysis: Purification of Copper
Electrolysis is applied in the purification of copper.
🔗 Process: It is used to refine impure copper to obtain high-purity copper.
Faraday's Laws
Faraday's laws provide mathematical relationships in electrolysis:
📏 First Law: 𝑚 = 𝐼𝑡 × 𝑀, where 𝑚 is the mass of substance liberated at an electrode, 𝐼 is the current in amperes, 𝑡 is the time in seconds, and 𝑀 is the molar mass.
📏 Second Law: 𝑉𝑅𝑇𝑃/𝑉𝑆𝑇𝑃 = 𝐹 × 𝑛, where 𝑉 is the volume of gas at room temperature and pressure (RTP), 𝑉𝑆𝑇𝑃 is the volume of gas at standard temperature and pressure (STP), 𝑅 is the gas constant, 𝑇 is the temperature in Kelvin, 𝑃 is the pressure, 𝐹 is Faraday's constant, and 𝑛 is the number of moles of electrons per mole of gas.
Faraday's Laws and the Faraday
Faraday's laws are essential in understanding the relationship between charge and the number of moles of electrons.
📊 Faraday: A Faraday represents a mole of electrons, which is equal to 𝐼𝑡.
Batteries: Dry Cell
Batteries, like dry cells, are devices that convert chemical energy into electrical energy.
🔋 Types: Dry cells are commonly used in portable devices and contain a paste electrolyte.
Batteries: Fuel Cell
Fuel cells are electrochemical devices that produce electricity through a chemical reaction involving a fuel and an oxidant.
🔋 Usage: Fuel cells have applications in powering vehicles and generating electricity.
