C3

• What is electrolysis?

  The process by which an electric current is passed through a compound, causing a chemical change
• What is an electrolyte?

  A compound in its liquid state that conducts electricity and contains mobile ions
• What are cations?

  Positive ions
• What are anions?

  Negative ions
• What happens during electrolysis?

  • positive ions gain electrons at the cathode and become atoms
  • negative ions lose electrons at the anode and become atoms
• What is the half equation for lead when it is discharged at the cathode?


  Pb2+ + 2e- -> Pb
• What is the half equation that forms bromine gas at the anode?


  2Br- -> Br2 + 2e-
• What happens during electrolysis of water?

  • hydrogen ions are discharged at cathode as hydrogen gas
  • hydroxide ions discharged at anode to form water and oxygen
• What is reduction?

  gain of electrons
• What is oxidation?

  loss of electrons
• What is the half equation that forms hydrogen gas at the cathode?


  4H+ + 4e- -> 2H2
• What is the half equation for hydroxide ions at the anode?


  4OH- -> 2H2O + O2 + 4e-
• What happens in electrolysis of aqueous solutions?

  Dissolved in water, so hydrogen and hydroxide ions are present that also participate in the reaction, less reactive one is discharged
• What are the rules for which ions are discharged in electrolysis of aqueous solutions?

  • At cathode, always hydrogen ions unless copper is present
  • At anode, always halides if present, if not hydroxide ions
• What is electroplating?

  A type of electrolysis that uses non-inert electrodes
• What does each component represent in electroplating?

  • cathode - the thing you want to coat
  • anode - metal you coat the object with
  • electrolyte - solution containing ions of the coated metal
• How does electroplating work?

  Metal ions from electrolyte are discharged onto the cathode and replaced by metal ions leaving the anode, repeats until anode is used up
• What happens during electroplating with silver?

  • silver atoms lose electrons at anode: Ag -> Ag+ + e-
  • silver ions gain electrons at cathode: Ag+ + e- -> Ag
• How is copper purified by electrolysis?

  Anode is made from impure copper, cathode from pure copper

  • During the process, cathode gains copper atoms and increases in mass, and anode loses copper atoms
  • Impurities fall off and collect underneath
• What does inert mean?

  unreactive
• Why does the electrolyte need to be liquid or molten?

  So ions are free to move around and go to their respective electrode
• What substance is mixed with aluminium oxide to lower its melting point?

  Cryolite
• Why is electrolysis not used to extract all metals?

  It is expensive and requires large amounts of energy
• What are strong acids?

  Acids that are fully ionised - all of their molecules release hydrogen ions
• What are weak acids?

  Acids that are partially ionised, are reversible
• What are dilute acids?

  Acids that contain a low ratio of acid to volume of solution
• What are concentrated acids?

  Acids that contain a high ratio of acid to volume of solution
• How is pH linked to hydrogen concentration?

  As the concentration of hydrogen increases by a factor of 10, pH decreases by a factor of 1
• What is a neutralisation reaction?

  A reaction between an acid and a base that produces a salt and water
• What happens during neutralisation in solution?

  Hydrogen ions from acidic solutions react with hydroxide ions from alkaline solutions to form water
• What is a redox reaction?

  A reaction in which reduction and oxidation occur at the same time
• If the pH is less than 7 the solution is..

  acidic
• If the pH is more than 7 the solution is..

  alkali
• If the pH is 7 the solution is..

  neutral
• What is an exothermic reaction?

  A chemical reaction that releases heat to surroundings
• What is an endothermic reaction?

  A chemical reaction that takes in heat from surroundings
• What are some examples of exothermic reactions?

  Combustion, neutralisation
• What is an example of an endothermic reaction?

  Photosynthesis
• What is activation energy?

  The minimum amount of energy required for the reaction to start
• What is a reaction profile?

  A chart that shows the energy involved in a reaction