SC10 - Electrolysis ✓
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SC10a - Define electrolysis
Electrolysis is a process that uses electricity to break down a chemical compound into its elements.
SC10a - Describe the relationship between positive and negative ions and their electrode, naming them.
• (Positive) Cations are attracted to the (negative) Cathode • (Negative) Anions are attracted to the (positive) Anode
SC10a - Why is an electrolyte able to conduct electricity?
• When an ionic solid is melted down or dissolved in water, its ionic bonds breaking meaning that the ions inside are now free to move. • This allows the electrolyte to conduct electricity.
SC10a - Describe the setup for an electrolysis exmperiment.
• Two electrodes (cathode and anode) are connected to a d.c supply. • They are also placed in the electrolyte (which is either molten or aqueous).
SC10a - At which electrodes do oxidation and reduction take place and how do these processes affect ions?
• Oxidation is the loss of electrons and takes place at the anode. Reduction is the gain of electrons and takes place at the cathode. • OIL RIG: • Oxidation Is Loss; • Reduction Is Gain
SC10a - Use half equations to display the oxidation and reduction of Zinc and Chlorine during electrolysis.
Zn2+ + 2e- → Zn (Reduction) 2Cl- → Cl2 + 2e- (Oxidation)
SC10a CP - Descirbe what you would expect to see when conducting the electrolysis of copper chloride solution using graphite (inert) electrodes.
• The cathode will be coated with a brownish layer. • This shows copper is being produced • At the anode there will be bubbles. • This indicates that a gas is being produced • If you hold a damp blue litmus paper near this, it will turn red and then bleach white. • This indicates that the gas produced is chlorine
SC10a CP - Describe how pure copper is obtained through the electrolysis of copper sulfate solution using copper electrodes.
• Anode - Impure Copper • Cathode - Pure Copper • Solution - Copper Sulfate Cu2+ ions from the anode move to the cathode, where they are deposited as copper ions. Impurities form as slude below the anode.
SC10b - How can you predict the products of electrolysis?
• When electrolysing a solution, water will always be present • This means H+ and OH- ions are always present • At the cathode, the metal can only be produced if it is less reactive than H+ • At the anode Oxygen will always be produced unelss the negative ion is a halide (has a charge of 1-) • If the electrolyte is molten, the components of the electrolyte will be produced
SC10b - Give the half equation for the oxidation of a Hydroxide Ion
4OH- -> O2 + 2H20 + 4e-
SC10b - Describe the tests for chlorine gas
• Chlorine wll turn a damp blue litmus paper red, then will bleach it white
SC10b - How do we test for oxygen gas?
• We hold a glowing splint to the gas - if it’s oxygen, the splint will reignite since oxygen supports combustion
SC10b - Explain why the electrolysis of acidified water produces 2x as much hydrogen as oxygen
In the formula H20, there is 2 hydrogens for every oxygen