electrolysis

• What is electrolysis?


  The breaking down of a substance using electricity
• Types of electrolysis


  Of aqueous ionic compounds

  Of molten ionic compounds
• Ionic compound


  a compound composed of positive(cations) and negative ions(anions)
• Why can't ionic compounds conduct electricity as solid?

  The electrons aren't free to move and carry the charge through the structure
• What is an electrolyte?

  a liquid/solution that conducts electricity
• Define discharge


  Gain/loss of electrons to become electrically neutral/ an atom
• What is the general rule for electrolysis of aqueous solutions regarding which ion gets discharged at each electrode ?


  The ion that is easiest to discharge will be discharged
• How are electrolytes made?

  by melting or dissolving ionic compounds
• What is the a positive electrode called?

  Anode
• What is a negative electrode called?

  Cathode
• reduction


  gain of electrons
• Oxidation


  loss of electrons
• Which electrode are cations discharged at ?

  Cathode
• Does oxidation or reduction occur at the cathode?

  reduction

  Cations are discharged at the cathode as they gain electrons to become atoms
• Which electrode are anions discharged at?

  Anode
• Does oxidation or reduction occur at the anode?

  oxidation

  Anions are discharged at the anode as they lose electrons to become atoms
• How do ions become atoms or molecules?

  By losing or gaining electrons
• How does an electrolysis circuit become complete?

  A flow of electrons taken from anode to cathode
• How do you measure the conductivity of an electrolyte?

  With a conductivity probe
• In molten ionic compounds there is only ___________

  one source of ions
• In the electrolysis of molten lead bromide what is the half equation for the Pb2+ ions?

  Pb2 + 2e --> Pb
• In the electrolysis of molten lead bromide what is the half equation for the Br- ions?

  2Br- -->Br2 + 2e
• What is an electric current?

  the flow of electrons
• What is a covalent bond?


  a shared pair of electrons
• Why can't covalent compounds conduct electricity?

  Because a covalent compound leaves no spare electrons in the outer shell so there are no free electrons to carry the current
• What is an ionic bond?

  when an atom loses or gains electrons to form charged particles
• Why can ionic compounds only conduct electricity when molten or in a solution

  an ionic compound in solid state forms a lattice so the ions aren't free to move around. when they are dissolved or melted the ions separate and are free to carry electrical currents
• What does aqueous mean?

  dissolved in water
• Which two ions could be discharged at the cathode from an aqueous solution ?

  H+ or cation from ionic compound
• Which two ions could be discharged at the anode from an aqueous solution ?

  OH- or anion from ionic compound
• Why is there a choice of two ions at each electrode to be discharged in an aqueous solutions?

  In water a small fraction of the molecules break down into H+ and OH- ions
• What is the rule for which anion will be discharged at the anode from an aqueous solution?

  O2 is produced from the discharge of OH- unless the ionic compound contains halide ions, in this case the halogen is produced

  E.g. 4OH- —> 2H2O+ O2+4e-
• What is the rule for which cation will be discharged at the cathode from an aqueous solution?

  Hydrogen produced from the discharge of H+ if ionic compound contains metal ions more reactive than hydrogen

  E.g. 2H+ +2e- —> H2
• Test for hydrogen gas


  Lit wooden splint

  Burns with a Squeaky pop
• Test for chlorine gas


  Bleaches damp litmus paper
• Test for oxygen gas


  Relights a glowing splint
• Reactivity series


  Potassium

  sodium

  Lithium

  calcium

  magnesium

  aluminium

  CARBON

  zinc

  iron

  Tin

  lead

  HYDROGEN

  copper

  silver

  gold

  Platinum
• Why are hydrogen and carbon included in the reactivity series?

  For comparison to determine how metals could be extracted
• Which elements are found as native metals?

  Gold

  It is so unreactive that it is found as a native metal and not a compound
• How are metals that are less reactive than carbon extracted ?

  By reduction with carbon