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# Electrolysis ## The Process of Electrolysis * When an electric current is passed through a molten ionic compound, the compound decomposes or breaks down. * The process also occurs for aqueous solutions of ionic compounds. * Liquids and solutions that are able to conduct electricity are called el...

# Electrolysis ## The Process of Electrolysis * When an electric current is passed through a molten ionic compound, the compound decomposes or breaks down. * The process also occurs for aqueous solutions of ionic compounds. * Liquids and solutions that are able to conduct electricity are called electrolytes. * Covalent compounds cannot conduct electricity hence they do not undergo electrolysis. * An electrolytic cell is the setup used in electrolysis, consisting of: * **Electrode:** A rod of metal or graphite through which an electric current flows into or out of an electrolyte. * **Electrolyte:** An ionic compound in molten or dissolved solution that conducts electricity. * **Anode:** The positive electrode of an electrolysis cell. * **Anion:** Negatively charged ion attracted to anode. * **Cathode:** The negative electrode of an electrolysis cell. * **Cation:** Positively charged ion attracted to the cathode ## The Basic Set-up of an Electrolysis Cell **(Diagram shows a basic setup of an electrolytic cell with a power supply, anode, cathode, and electrolyte solution.)** ## Examiner Tip Use the PANIC mnemonic to remember which electrode is positive and which is negative: Positive (is) Anode, Negative is Cathode. ## Ionic Compounds and Electrical Conductivity * Ionic compounds in the solid state cannot conduct electricity since they have no free ions that can move and carry the charge. * The ions must be able to move, only in molten state or when dissolved in a solution (usually aqueous). * When the cell is turned on and an electric current is passed through an electrolyte, the ions in the solution start to move towards the electrodes. ## Electrical Conductivity of Ionic Compounds **(Diagram illustrates the difference in ionic compound structure in solid and molten/solution states.)** * **Solid State:** Particles in fixed position * **Molten/Solution:** Particles can move around ## Processes During Electrolysis * During electrolysis, electrons move from the power supply towards the cathode. * Electron flow in electrochemistry occurs alphabetically, electrons flow from the anode to the cathode. * Positive ions within the electrolyte migrate towards the negatively charged electrode (cathode). * Negative ions within the electrolyte migrate towards the positively charged electrode (anode). ## Diagram showing direction of movement of electrons and ions in electrolysis of NaCl **(Diagram describes the movement of electrons and ions within an electrolyte solution during electrolysis.)** ## Examiner Tip * When a metal conducts, electrons move through the metal. When a salt solution conducts, ions in the solution move towards the electrodes while carrying electrons. ## Electrolysis of Ionic Compounds * Lead(II) bromide is a binary ionic compound. * When these compounds are heated beyond their melting point, they become molten and can conduct electricity as their ions can move freely and carry the charge. * These compounds undergo electrolysis and always produce the corresponding elements. * To predict the products of any binary molten compound, first identify the ions present. * The positive ion will migrate towards the cathode and the negative ion will migrate towards the anode. * Therefore, the cathode product will always be the metal and the product formed at the anode will always be the non-metal. ## Diagram showing electrolysis of lead(II) bromide **(Diagram illustrating the electrolysis of lead (II) bromide; shows the movement of ions, electrons, and the formation of products.)** ## Examiner Tip Remember that electrodes need to be inert (e.g., graphite or platinum) so that they don't participate in a side reaction with the electrolyte.