electrolysis

• what is electrolysis 


  the process where an ionic compound can be split up using electricity
• where do positively charged ions move to?

  the cathode (negative electrode)
• where do the negative ions move to?

  the anode (positive electrode)
• why do compounds not conduct electricity when solid?

  because their ions are in a fixed position however once melted the ions are free to move around within the hot liquid to carry electrodes
• are the anode reduced or oxidised?

  the negative ions lose electrons which flow through the circuit meaning they have been oxidised
• are the cathode reduced or oxidised?

  the positive ions gain electrons from the circuit meaning they have been reduced
• why is aluminium oxide mixed with molten cryolite

  to reduce the amount of energy to extract aluminium
• what does aluminium oxide produce during electrolysis

  aluminium ions and oxide ions
• why are carbon anodes replaced regularly

  they gradually burn away as the oxygen reacts with the carbon anode forming carbon dioxide gas
• in aluminium oxide what forms at the cathode and what forms at the anode

  aluminium forms at the cathode and oxygen forms at the anode
• where is hydrogen produced in a aq solution

  hydrogen is produced at the cathode if the metal is more reactive than hydrogen
• what is happening in the half equation: 2Cl -> Cl2 + 2e-

  the negative chlorine ions are attracted to the positive electrode and each lose 1 electron. the chloride ions are oxidised and given off as chlorine gas
• what is happening in the half equation: 2H+ + 2E- -> H2

  the positive ions are attracted to the negative electrode. they gain 1 electron and the hydrogen ions are reduced and given off a hydrogen gass
• what is produced in sodium chloride?

  chlorine gas is produced at the anode, hydrogen gas is produced at the cathode
• why is electrolysis used to extract some metals

  if those metals are more reactive than carbon
• aluminium is produced by electrolysis of a molten mixture. what 2 substances does the molten mixture contain


  aluminium oxide, cryolite
• why are aluminium ions reduced

  to form aluminium atoms
• practicle: how do you test for halogen gases?

  use damp, blue litmus paper. If there is any chlorine gas present in the test tube then holding the litmus paper inside the test tube should cause it to be bleached and will turn white. 
• what is a hypothesis

  a proposal intended to explain certain facts of observation
• he conducting liquid in electrolysis is called an electrolyte and has free moving ions.
• the metal that forms at the cathode during electrolysis is always less reactive than the metal that forms at the anode.
• electrolytes can only conduct electricity when they are melted or dissolved in water.
• in electrolysis, the positive ion moves towards the negative electrode (cathode) and the negative ion moves towards the positive electrode (anode).
• when sodium chloride solution is used as an electrolyte, chlorine gas is produced at the anode and sodium metal is deposited on the cathode.
• during electrolysis, the products formed depend on which element is more reactive.