Electrolysis and Electrochemical Cells

• Chapter 13 explores electrochemistry

Electrochemistry Objectives

• Electrolysis involves the conduction of electricity through molten or dissolved ionic compounds (electrolytes), resulting in chemical changes like decomposition at the electrodes.
• Electrolysis is the evidence of ions existing in a lattice when solid but become mobile when molten or in solution.
• The mobility of ions and the resulting electrode products explain the electrolysis of molten sodium chloride using inert electrodes.
• Likely products of the electrolysis of a molten binary ionic compound can be predicted using inert electrodes.
• The idea of selective discharge is based on:
• Cations, is determined by the reactivity series
• Anions, involves halides, hydroxides, and sulfates like in aqueous copper(II) sulfate and dilute sodium chloride (electrolysis of water)
• Concentration effects, like in the electrolysis of concentrated and diluted aqueous sodium chloride. (Inert electrodes are used in all cases above)
• Likely products of the electrolysis of an aqueous electrolyte can be predicted using relevant information.
• Ionic equations for the reactions at the electrodes during electrolysis can be constructed, given relevant information.
• Electrolysis of aqueous copper(II) sulfate with copper electrodes describes the process of purifying copper.
• Electroplating of metals like copper plating are described, along with applications.
• Production of electrical energy is described, using simple cells with two electrodes in an electrolyte, linked to the reactivity series and redox reactions via electron transfer.
• Hydrogen from water or hydrocarbons can be used as a potential fuel, reacting with oxygen to generate electricity directly in a hydrogen fuel cell.

What is Electrolysis?

• Electrolysis involves using electric current to chemically separate a compound into its components and the flow of electricity through water will cause the water to breakdown into hydrogen and oxygen.
• Electrolysis uses electricity to breakdown or decompose a compound, typically an ionic compound, in a molten or aqueous state.
• Electrolysis process happens in an electrolytic cell and converts electrical energy into chemical energy.

Parts of an Electrolytic Cell

• Electrolysis requires a power supply or a power source, like a battery that drives the movement of charges around a circuit.
• Electrodes are connected to opposite ends of the power supply.
• An electrolyte is required, in which the electrodes are immersed.
• The battery acts as an electron pump, moving electrons from the anode to the cathode, and electrons enter the battery from the anode and are pumped out to the cathode.
• An electrolyte is an electrically conductive substance in the molten or aqueous state, conducts electricity with the use of mobile ions
• Electrolytes act as mobile charge carriers to conduct electricity.
• Examples of electrolytes include dilute sulfuric acid, molten sodium chloride, and copper(II) sulfate solution
• Electrodes contain delocalized mobile electrons to conduct electricity.
• The anode is the positive electrode connected to the positive terminal of the power source.
• The cathode is the negative electrode connected to the negative terminal of the power source.
• Examples of electrodes include metal plates and carbon (graphite) rods.

Types of Electrodes

• Electrodes must be electrical conductors that conduct electricity via the movement of delocalized mobile electrons found in their structures.
• Inert electrodes do not undergo chemical changes and don't take part in the electrolysis reaction, includes graphite and platinum.
• Reactive electrodes consist of metal anodes and undergo oxidation during electrolysis, like copper and silver.

Electrolysis

• In electrolysis charges are carried through the circuit using electrons and through the electrolyte using ions.
• In the external circuit, electrons move from the negative terminal to the positive terminal of the power supply.
• Within the electrolyte, the movement of ions inside the electrolyte completes the circuit.
• Anions are attracted to the positively-charged anode and lose electrons to become oxidized.
• Cations are attracted to the negatively-charged cathode and gain electrons from the cathode and become reduced.
• Atoms or molecules form when anions and cations are oxidized and reduced, and the process is called the discharging.
• An ionic compound must be dissolved in water (aqueous state) or melted (molten state) before it can be an electrolyte and conduct electricity.
• Ionic compounds are electrolytic conductors.
• Electrolytes undergo redox reactions at the electrodes to form new substances.
• In solid state, ions' fixed positions and immobilization prevent electrical conduction.
• In the molten and aqueous state, mobile ions enable the electrolyte to electricity

Electrical vs Electrolytic Conductors

• Electrical conductors, like metals and graphite, conduct electricity using delocalized mobile electrons from one end to the other, and the substance stay chemically unchanged.
• Electrolytic conductors (electrolytes) conduct electricity using mobile ions, causing substances to breakdown and create new products.

Molten Binary Ionic Compounds

• A molten binary ionic compound is typically a salt containing only one cation and one anion in the liquid state.
• Examples of molten binary ionic compounds include ions present, sodium chloride, NaC/(I), magnesium bromide, MgBr2(I), aluminium oxide, Al2O3(1), and iron(III) nitride, FeN.
• When molten sodium chloride (NaCl) is electrolyzed, sodium ions gain electrons and are reduced to form sodium atoms while chloride ions lose electrons and are oxidized to form chlorine molecules.
• Grey globules of sodium are found at as the cathode and yellow-green chlorine gas is found at the anode
• Overall equation: 2NaCl(I) → 2Na(I) + Cl2(g)
• Total number of electrons leaving the electrolyte via the anode is always equivalent to the number of electrons entering the electrolyte through the cathode.
• Electrolysis determines the overall equation and demonstrates equal mole ration for products.

Electrolysis Equation Steps

• Step 1: Involve writing the half-equations.
• Step 2: Balance the number of electrons gained or lost.
• Step 3: Combine the half equations from step 2.
• Step 4: Eliminate same electrons on both sides of the equation.
• Step 5: Write the overall equation
• The ratio of Na to CI2 produces is 2: 1.
• Contamination of products occur from the electrodes taking part in electrolysis.Therefore Inert electrodes are commonly used as they are usually made with unreactive substances.

Inert Electrodes

• The advantages of graphite:
  • High melting point
  • Will not melt if used in the electrolysis of molten binary ionic compounds
• Disadvantages of Graphite:
  • graphite will react with oxygen gases under high temperatures to produce carbon dioxide.
  • Graphite anodes must be replaced periodically.
• Advantage of platinum:
  • Does not take part in the electrolysis reaction
• Disadvantages of platinum:
  • lowers melting point compared to graphite
  • Might melt when used in the electrolysis of molten binary ionic compounds
  • Mostly used in the electrolysis of aqueous electrolytes.

Electrolysis of Molten Lead(II) Bromide

• At the cathode, lead ions gain electrons to form a lead the lead atoms form grey glubules
• At the anode, Bromide ions lose electrons and chlorine molecules are from the anode to form as red-brown bromine gas.

Aqueous Solutions

• Aqueous solutions result when a solute dissolves in water.
• Water has hydrogen ions (H⁺) and hydroxide ions (OH⁻) from the reversible dissociation of it’s molecules given H2O(I) = H⁺(aq) + OH⁻(aq)
• With an aqueous ionic substance, an electrolyte will contain two types of cations and anions, exemplified that in aqueous solutions, sodium chloride, NaCl(aq) splits into from dissolved substance of ions, and from water ions.

Selective Cation Discharge

• Metals can be ordered by their electrochemical reactivity.
• The metal, that is more electrochemically stable becomes harder to convert to the ion state.
• Copper 2+(Cu2+) and Ag+(silver) are in a solution if Ag+ion are being used, silver will be more used for the cathode because it is more selective.
• Metals that are above hydrogen in the reactivity series, discharge in a practical sense as the concentration of H+ ions is in a higher amount than the concentration of OH- ions.

Selective Anion Discharge

• The electrochemical series ranks anions by electrochemical reactivity, and the lower the position of the anion in dilute solutions, the more likely it will be selectively discharged.
• OH will discharge more selectively in a Chlorine solution.
• In OH half equations for ionic discharge is: 4OH(aq) → 02(g) + 2H2O(l) + 4e⁻

Solutions on Anions

• Selective discharge depends on the solution’s level of concentration. As the concentration increases, it increases with Cl⁻, Br⁻, I⁻ ions it can sometimes override the electrochemical series. Like NaCl if it’s concentrated and electrolysed the ions present is chlorine ions.
• 2Cl⁻(aq) → Cl2(g) + 2e⁻ half electrolyte for ionic discharge.

Electrolysis of products for Aqueous Solutions

• Apart from the products obtained from the anode and cathode in electrolytes, it is important to consider ions after electrolysis to make up electrolyte product.

Key Electrolysis Steps

• Step 1: Check the present ions within the electrolyte.
• Step 2: check for determination that there will be a half-equation will occur that will write the anions discharged from the anode.
• Step 3: check for the cation that discharges from the cathodes that half a equations.
• Step 4: check and write out the overall reactions.
• Step 5: identify both cation and anions that exist to electrolyte products.
• Electrolysis is done when aqueous sodium chloride (NaCl) has been diluted through electrolyte that contains H+ and Na ions .
• Anode has chlorine gas as a ion(CI), and a hydroxide ion(OH) that causes hydrogen to be released from cathode ions to go to H2(g) .
• Hydrogen being lower than sodium due to reactivity levels increases the hydrogen when discharging them to have selective ways. And the other electrolyte is colourless hydrogen gas
• OH that has chloride ions from the anionic electrochemical increases selectively discharge colourless oxygen gas, increasing the solutions level and sodium level
• Sodium chlorides concentration is 2:1.

Solutions in Overall Equations

• Step 1: In half equations, hydrogen increases to the half ion.
• Step 2: electrons are gained or will lose as the half ion from hydrogen increases, sodium has more equations with both cathode and anode at 4OH(aq) → 02(g) + 2H2O(1) + 4e⁻ .
• step 3: Combine half equations with OH level.
• Step 4: eliminate electrons by cancelling sides of the equation using 4H+(aq) + 4e⁻ + 4OH(aq) → 2H2(g) + O2(g) + 2H2O(l) + 4e - .
• Step 5: Write both the anionic and cation from the electrolytes reaction levels.

Solutions of Concentrations for Sodium Chloride.

• Electrolysis in water has equation diagram for its equivalent electrolytes.
• Chloride levels for solutions is selective and can be increased via concentrated levels with H+ ions

Electrolysis of Concentrated Sodium Chloride

• In electrolyte concentrations, it is shown concentrations that are high influence electrolyte and is discharge and colour high concentrations of hydrogen gas and is selective with yellow gas

Combining Two Halves Eqations

• 2H+(aq) + 2Cl⁻(aq) → H2(g) + Cl2(g)
• Solutions become alkaline and release H+ ions, sodium levels form in hydraxides from the alkaline solutions. When drops are added, ions in indicators add from violet green and cathode can show concentrations.

Electrolysis for Equations(cathode and anode).

• Electrolytes can state ions via the levels of H⁺s.
• Dilution for sulphuric acids can state H+ and OH levels.

Industrial Electrolysis

• The electricity utilized in daily lives is carried by wires that have electrons.
• Copper, because of its positive electrons for conductivity levels and good pricing, helps wires stay intact. Electrolysis utilizes copper in purification.
• Reactive electrodes allow electrolyte processes to participate. Industries use electrodes mostly with electrolytes.
• Anodes and cathodes are useful due to the reactive metals used to form metal cathodes that cathode that react to it.
• Copper reacts with electrolysis during reactions as they increase with metal that dissolves.
• With copper electrodes, ions discharge electrolyte and are not active to use SO for reactions.
• Copper will dissolve to form ion and increase in mass with selectivity after the hydrogen
• Electrolytes that are used or deposited onto the cathodes is dissolved to increase concentration on the blue of the electrolyte

Electrolysis Applications

• metal purification is when a raw impure can cause anode slimes to form a copper sulfate level electrolyte
• Electroplating: electroplate allows coat for object plating to occur and plating and be in constant motion through aqueous solution.
• Can coat a copper metal as the cathode increases in weight. Electrolysis of corrosion occurs as a factor to use for graphite that occurs when they electrolytes.
• Graphite makes electroplating very corrosion resistant.

Simple Cells

• Similar to that of electrolytic cells and it has aqueous solutions to act as electrodes.
• A simple cell contains electrical activity from chemical energy.
• Structure of a simple cell requires:
  • Two metals with electrodes
  • Electrolyte: electrolyte like oxidation causes anode activity and reduce cathode.

Metal Battery Activity

• Acts and cathodes caused gain in electrons to have electrolyte produce circuits to work and gain reduction.
• The electrodes that spontaneously release electrons where and anodes produce electrical activity.

Electrical Cells Electrolytes

• In simple cells electrolytes allow chemicals to flow more freely and supply more more external batters or high levels
• Metal can gain more electrodical to produce more greater and the more voltage can produce.
• Copper on the cathode and the anodes generate more increase to have more current.

Hydrogen with Simple Cells

• Is used to increase power and electrolyte and oxidized.
• Only generates to not increase on climate change to create more heat or energy and electrolysis.
• Electrolyte is produced by high electricity.
• With graphite electrodes on concentration and produce it is safe. more expensive hydrogen to produce as byproduct

Explore electrolysis, electrolytic cells, and their applications. Questions cover the role of electrolysis, factors affecting cation discharge, and purposes of electroplating. Investigate fuel cells and voltage production in batteries.