BMAT - Chemistry Electrolysis Review Questions and Answers

Electrolysis Compounds are broken down into simpler substances using electricity. In order to work, ions must be free to move so need to be dissolved in water or melted Electrolyte The liquid that conducts electricity How does electrolysis work There is a flow of electrons that are taken away from the positive electrode and given to other ions at the negative electrode. As ions gain or lose electrons they become atoms/molecules and are then released. Positively charged ions move to negative electrode and negatively charged ions move to positive electrode. Always involves redox What current in used in electrolysis and why Direct current as the charged move towards opposite electrodes and this requires the electrodes to maintain polarity which is only possible with DC as AC will cause the polarity to be continuously changing Cathode Negative electrode where cations (positively charged ions) are reduced Anode Positive electrode where anions (negatively changed ions) are oxidised Electrolysis of lead bromide (PbBr2) At the cathode, Pb2+ ions are attracted and accept two electrons so are reduced producing lead metal. At the anode, Br- ions are attracted and they give away an electron to form bromine which pair yo form diatomic bromine Br2 Electrolysis of lead bromide (PbBr2) half equations Pb2+ + 2e- - Pb 2Br- - Br2 + 2e- Electrolysis of Sodium chloride solution (NaCl) At the cathode, if metal and H+ ions are present the metal with stay in solution and Hydrogen will be produced if the metal is more reactive than the Hydrogen so H+ ions are attracted and 2 H+ ions accept two electrons to become on Hydrogen molecule. At the anode, if OH- and halide ions are present, the halogen molecule will form but if there is no halide present then Oxygen will form. Sodium ions stay in solution as they're more reactive than hydrogen and hydroxide ions from the water also stay so NaOH is formed. Electrolysis of Sodium chloride solution (NaCl) half equations 2H+ + 2e- - H2 2Cl- - Cl2 + 2e