| Why can ionic compounds conduct electricity when molten/dissolved in water? | The forces of attraction are broken and the ions are free to move and conduct electricity - these are electrolytes |
| What happens during electrolysis in terms of electrons | 1) Positive ions attracted to (negative) cathode, gaining electrons and forming atoms - reduction
2) Negative ions attracted to (positive) anode, losing electrons and forming atoms - oxidation |
| How are metals extracted | ||
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| Explain the process of extracting aluminium using electrolysis. | 1) Mixed with cryolite - lowers melting point reducing amount of energy needed and saving money
2) Apply an electric current to the molten aluminium oxide - ions free to move
3) Cath/anode are made of graphite - a form of carbon which is a very good conductor of electricity and has a very high melting point and can therefore be used at high temps
4) Reduction: Al3+ attracted to (-) cathode gaining 3 electrons forming an atom: Al3^(+) + 3e^(-) -> Al
5) Oxidation: 2^(-) attracted to (+) anode losing 2 electrons forming an atom: O2^(-) -> O + 2e^(-) |
| What's the definition of electrolysis? | Electrolysis is the process by which ionic substances are decomposed (broken down) into simpler substances when an electric current is passed through them. Electricity is the flow of electrons or ions |
| Why must the anodes be replaced regularly during electrolysis? | They are made of carbon, the oxygen molecules produced at the anode react with the graphite (carbon), forming carbon dioxide gas |
| Why's electrolysis expensive? | - Melting the compounds such as aluminium oxide requires a great deal of energy
- A lot of energy is required to produce an electric current |
| What additional factor must we consider for electrolysis of aqueous solutions compared to electrolysis of molten compounds? | - Water is also involved - water ionises (splits) & could therefore possibly move to the electrodes
- Hydrogen (H+) is produced at the cathode if the other '+' charged ion is more reactive than hydrogen (refer to the image below) |
| What's usually produced at the anode during electrolysis of aqueous solutions & what is the exception? | - Oxygen
- The exception: if the aqueous solution contains halide ions (Group 7) than the halogen will be produced at the anode |
| Explain the required practical: Electrolysis of aqueous solutions - Copper (II) Chloride | 1) Pour 50cm3 of copper (II) chloride solution into beaker
2) Place plastic petri dish (with 2 holes) over beaker and place each graphite rod into each hole - electrodes (carbon graphite is unreactive so the electrodes are inert - wont react). Make sure the electrodes don't touch each other - else it'll cause a short circuit
3) Attach crocodile clips to the rods and connect the rods to the terminals of low-voltage power supply, select 4V on the power supply and switch it on
4) The (-) cathode will become coated in copper, copper's less reactive than hydrogen and will therefore be discharged at the cathode
5) At the anode, bubbles of gas will also be produced and you may smell chlorine in the air, chlorine is a halide ion and will therefore be discharged at the anode
6) Placing a damp blue litmus paper near the anode and it becomes bleached proves chlorine is present |
| Explain the required practical: Electrolysis of aqueous solutions - Sodium Chloride | 1) Pour 50cm3 of sodium chloride solution into beaker
2) Turn on low voltage power supply
3) Anode: bubbles of gas produced which bleach damp blue litmus paper - chlorine, because chlorine is a halide ion, it is discharged at the anode
4) Cathode: bubbles of gas produced - hydrogen, hydrogen is discharged at the cathode as it is less reactive than sodium
5) We can prove hydrogen is produced at the cathode by collecting it then testing it with a lit splint, it'll produce a squeaky pop |
