14164305
Description
Flashcards by Farha Idrees, updated more than 1 year ago
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Created by Farha Idrees
almost 6 years ago
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| Question | Answer |
| What is electrolysis? | the process in which ionic substances break down into simpler substances when an electric current is passed through them |
| How and why is an electric current passed through a substance? | A liquid must be used, being either: 1. a molten ionic substance 2. an aqueous solution this is because their ions are free to move and carry their charges to the electrodes |
| Give an example of why the electrolyte needs to be liquid. | if you heat table salt, or sodium chloride, at over 801C, it will melt ↓ the liquid will contain free-flowing positive sodium ions and negative chloride ions ↓ this simply means that the sodium and chloride ions are free to move within the liquid and can carry a charge |
| Define: a) electrolyte b) anode c) cathode d) cation e) anion | a) electrolyte: the compound which is broken down b) anode: positive electrode c) cathode: negative electrode d) cation: positive ion e) anion: negative ion |
| Describe the process of electrolysis | → you have two electrode, conducting rods, which dip into the electrolyte and have a gap in between → one of these are connected to the positive terminal of a power supply, a positive electrode - the anode → the other electrode is connected to the negative terminal, the cathode → during electrolysis, positively charged ions move towards the cathode and at the same time, the negative ions move to the anode as opposite charges attract → when the ions reach the electrodes, they lose their charge and become elements |
| What happens at the electrodes? | • gases may be given off • metals deposited depending on whether it is: • molten • dissolved in water |
| Describe the electrolysis of zinc chloride. | The zinc chloride is a molten compound and the electrolyte: • cathode; the positive zinc ions become solid zinc atoms • anode: the negative chlorine ions become chlorine gas molecules |
| Describe the redox reaction at the electrode. | • at the positive electrode (anode), negative ions lose their electrons, so are oxidised • at the negative electrode (cathode), positive ions gain their electrons, so are reduced |
| Explain, in terms of reduction and oxidation, using half equations, what happens at the electrodes during the electrolysis of lead bromide. | CATHODE: • negative electrode- attracts the positive lead ions • gains ions = reduction 2e- + Pb2+ → Pb ANODE • positive electrode- attracts negative bromine ions • loses ions = oxidation 2Br - 2e- → Br2 |
| In aqueous solution, electrolysis is more complex because of the water. What are the ions formed by water? | H2O → OH- + H+ |
| If two elements can be formed at an electrode - | - the less reactive element will usually be formed. |
| What happens at the cathode in an aqueous solution? | • negative electrode = positive ions, gains electrons • the less reactive product will be formed, either hydrogen or the metal, is usually produced • if hydrogen was formed: 2e- + 2H+ → H2 |
| What happens at the anode in an aqueous solution | • positive electrode = negative ions, loses electrons • either the hydroxide ions are discharged or the halogen ions, if it contains a high concentration of halide ions (Group 7) • if the hydroxide was formed 4OH- → 2H2O + O2 + 4e- • if the halogen was formed 2Cl- → Cl2 + 2e- |
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