Topic 3: Chemical Reactions - Subtopic 4: Electrolysis
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What is electrolysis?
Where an electric current is passed through a molten ionic compound and the compound breaks down
True or False: Electrolysis does not occur with solutions
False, process occurs for aqueous solutions of ionic compounds
What are liquids and solutions that can conduct electricity known as?
Electrolytes
What compounds cannot conduct electricity?
• Covalent Compounds • Cannot undergo electrolysis
What is an electrode?
A rod of metal or graphite through which an electric current flows into or out of an electrolyte
What is an electrolyte?
Ionic compound in molten or dissolved solution that conducts electricity
What is an anode?
Positive electrode of electrolysis cell
What is a cathode?
Negative electrode of electrolysis cell
What is an anion?
Negatively charged ions attracted to anode
What is an cation?
Positively charged ions attracted to cathode
Why can’t ionic compounds conduct electricity?
Have no free ions that can move and carry charge
What is an electrolytic cell?
Name given to set-up used in electrolysis
Where do electrons move during electrolysis?
Power supply to cathode
What does an aqueous solution always contain?
Ions from dissolved ionic compound and hydrogen and hydroxide ions (produced by water in solution)
What occurs at the anode during electrolysis of an aqueous solution?
• Negatively charged OH⁻ and non-metal ions are attracted to anode • If there are halide ions present, halide ion is discharged, loses electrons and form halogen • If no halide ions are present, OH⁻ is discharged at anode, loses electrons and forms oxygen. • In both cases, other ion remains in solution
What occurs at the cathode during electrolysis of an aqueous solution?
• Positively charged H⁺ and metal ions are attracted to cathode • If metal is above hydrogen in reactivity series, hydrogen is produced causing effervescence at cathode • If metal is below hydrogen in reactivity series, ion of that metal is discharged and accumulates at cathode • In both cases, other ion remains in solution
What are inert electrodes?
• Don’t take part in process • Made from unreactive metals • Provide surface for reactions to happen on
What are non-inert electrodes?
Electrodes are used which will take part in electrolysis reaction for electroplating and purifying copper
What is a simple cell?
Source of electrical energy
What is the simplest design of a cell?
• Two electrodes made from metals of different reactivity immersed in an electrolyte • Connected to an external voltmeter by wire, creating a complete circuit
What is a common example for electrodes for a simple cell?
• Zinc (more reactive metal and forms ions more easily, readily releasing electrons) • Copper
What does the electrons give the more reactive electrode?
• Negative charge • Sets up charge difference between electrodes • Electrons flow around circuit to copper electrode which is now the more positive electrode
What does the difference in the ability of the electrodes to release electrons cause?
• Voltage to be produced • Greater difference in reactivity, greater voltage produced • Electrolyte also affects voltage as different ions react with electrodes in different ways
Until when do cells produce a voltage?
• Produce voltage until a reactant is used up