electrolysis

• In electrolysis, an electric current is passed through an electrolyte, which is a substance that conducts electricity when dissolved in water or melted.
• During electrolysis, positive ions migrate towards the negative electrode (cathode) and negative ions migrate towards the positive electrode (anode).
• An ionic compound will break up to form its component ions during electrolysis.
• solid ionic compounds do not conduct electricity as the ions cannot move. To undergo electrolysis they must be molten or dissolved, so ions are free to move
• solid ionic compounds can also undergo electrolysis when in dissolved water
• it requires less energy to dissolve ionic compounds in water than it does to melt them . however in the electrolysis of solutions, the pure elements are not always produced. This is because the water can also undergo ionisation: H20 + e- → H+ + OH-
• Products at the anode:in electrolysis of a solution, if the metal contains oxygen then oxygen gas is formed at the anode the OH- ions formed from the ionisation of the water are attracted to the anode the OH- ions lose electrons to the anode and form oxygen gas: OH- -> 02+H2O+e-

  if the non metal ion is a halogen ,then the halogen gas is formed at the anode
• products at the cathode: in electrolysis of a solution, if the metal contains hydrogen then hydrogen gas is formed at the cathode the H+ ions formed from the ionisation of the water are attracted to the cathode the H+ ions gain electrons from the cathode and form hydrogen gas: H+ + e--> H2
• to test for chlorine gas , collect the gas in a test tube and insert damp litmus paper - the litmus paper will bleach white
• to test for oxygen gas , light a splint with the gas and observe whether it burns with a pop and hiss (oxygen) or a dull flame (nitrogen)
• to test for hydrogen gas , collect the gas in a test tube and insert a glowing splint into the gas- it should burn with a squeaky pop noise
• to extract aluminium oxide by electrolysis you first have to mix it with cryolite which lowers the melting point , then the mixture is heated until it is molten, finally the molten mixture undergoes electrolysis

  Al2O3[l]-->Al[l]+O2

  Cathode : pure aluminium - Al3+ [l]+3e--->Al[l]

  Anode: oxygen is formed - O2- [l]-->O2[g] +4e-
• in the electrolysis of aluminium , the anode is made of graphite. The graphite reacts with the oxygen to form carbon dioxide and so slowly wears away. It therefore needs to be replaced frequently .
• Electrolysis is a technique used to split compounds into their elements by passing an electric current through an electrolyte
• For insoluble compounds like most metal oxides, they need to be melted to make them a molten liquid for the electrolysis process
• For soluble compounds like copper sulfate and sodium chloride, they can be dissolved in water to make the electrolyte
• In an electrolysis experiment, you need a beaker full of electrolyte, two electrodes (positive anode on the right, negative cathode on the left), a wire joining the electrodes, and a power supply
• The cathode (negative electrode) attracts positive ions, such as the metal ion from the compound and the hydrogen ion from water
• The cathode will discharge the ion of the least reactive element, following the reactivity series
• If hydrogen ions and ions of less reactive metals are present, hydrogen ions will be discharged
• If copper ions are present, they will be discharged as copper is less reactive than hydrogen
• The anode (positive electrode) will discharge either negative ions from the compound or hydroxide ions
• If halides (fluoride, chloride, bromide, etc.) are present, they will be discharged at the anode
• If halides are not present, hydroxide ions will be discharged at the anode
• In an aqueous solution of copper sulfate, copper ions will be discharged at the cathode to form pure copper, while hydroxide ions will be discharged at the anode to form oxygen and water
• In an aqueous solution of sodium chloride, hydrogen ions will be discharged at the cathode to form hydrogen gas, and chloride ions will be discharged at the anode to form chlorine gas