C6 - Electrolysis Flashcards
What is electrolysis?
The breakdown of a substance using electricity.
How are ionic compounds electrolysed?
When they are molten or dissolved in water because their ions are then free to move and carry their charge to the electrodes.
What happens during the process of electrolysis?
- Positive ions move to the cathode (negative electrode).
- Negative ions move to the anode (positive electrode).
What happens at the cathode (N) during electrolysis?
Positive ions gain electrons, so they are reduced.
What happens at the anode (P) during electrolysis?
Negative electrons lose their extra electrons so they are oxidised.
What happens when electrolysis occurs in aqueous solution?
- The less reactive element, either hydrogen or the metal is usually produced at the cathode.
- At the anode, oxygen gas is given off from discharged hydroxide ions produced from water or a halogen produced if thee electrolyte is a solution of a halide.
What is electrolysed in the extraction of aluminium metal?
Aluminium oxide from the ore bauxite.
Why is aluminium oxide mixed with molten cryolite?
- To lower its melting point reducing the energy needed to extract the aluminium.
What happens in electrolysis during the extraction of aluminium?
- Aluminium forms at the cathode.
- Oxygen forms at the anode.
Why are carbon anodes replaced regularly?
- They gradually burn away as the oxygen reacts with the hot carbon anodes, forming carbon dioxide gas.
What happens when you electrolyse sodium chloride solution?
3 products, chlorine gas and hydrogen gas given off at the electrodes, plus sodium hydroxide solution left in the solution.
Where is hydrogen produced in aqueous solution?
- At the cathode as H+(aq) ions are discharged from solution in preference to Na+(aq) ions.
Where is chlorine produced in aqueous solution?
At the anode as Cl-(aq) ions are discharged from solution in preference to OH-(aq) ions.
