11-12

• What is ELECTROCHEMISTRY?


  In each of them an electron is transferred from one species to another.
• What are redox reactions?

  Together with acid-base reactions (transfer of protons)
• – What is Oxidation?

  Oxidation is the loss of electrons
• What is Reduction?

  Reduction is the gain of electrons
• What does Oxidation And Reduction to a the number? Oxidation increases oxidation number. Reduction decreases oxidation number
• General rules of oxidation numbers: part 1: 1. Oxidation number of an element not combined with other elements = 0 • e.g. for Mg = 0; Cl in Cl2 = 0 2. Oxidation number of an ion equals its charge • e.g. for Fe2+ = +2; Cl- = -1 3. Specific oxidation numbers • H is +1 with non-metals • O is -2 (for most compounds –except H2O2).
• General rules of oxidation numbers: part 2: 4. Sum of the oxidation numbers of all atoms in a neutral molecule equals 0 • e.g. for H2O (2*(+1) + 1*(-2) = 0) 5. Sum of the oxidation numbers of all atoms in a polyatomic ion equals the total charge • e.g. oxidation state of Mn in MnO4 – XMn + 4*(-2) = -1 XMn = -1 + 8 = +7
• Some exceptions For Elements oxidisation numbers: • – F is always -1 in compounds with other elements. Cl, Br and I are always -1 except when combined with oxygen: ClO- : Cl = +1, O = -2 – H is +1 except when it forms a compound with a metal: CaH2: Ca = +2, H = -1 – O is -2 in most compounds except: H2O2 : H = +1, O is -1
• What are the agents and definition?

  Oxidant agent; means which one loosed electrons

   

  Reducing agent: gaining electrons
• Summary of Oxidisation and Reduction: Summary • Oxidation and reduction occur together • Oxidation is loss of electrons • Reduction is gain of electrons • The oxidising agent is reduced • The reducing agent is oxidised • An oxidation number is the charge that an atom would have if the bonding was ionic.
• what is the Oxidising Agent and Reducing Agent?

  Reducing Agent: Something that reduces the oxidation state of another atom (the reducing agent gets oxidised) • Oxidising Agent: Something that increases the oxidation state
• What Electrochemical cells?


  A device in which an electric current can happen. produced by a spontaneous reaction (galvanic cell) or An electric current causes a non-spontaneous reaction to occur (electrolytic cell)
• what occurs in the anode?


  Oxidation
• what does oxidised species release? oxidised species release electrons into the anode •(-) polarity
• What occurs in cathode?

  Reduction
• What does the reduced species do? They collect electrons from the cathode
• How electricity transfer from anode to cathode?


  Conducting wire enables e- transfer
• What does the anode and cathode do? anode dissolves and the cathode precipitates.
• What completes the circuit?

  Salt bridge “completes the circuit” and provides ions to each electrolyte solution Galvanic cell is now complete
• What reactions occur at each electrode?

  Two chemical reactions occur in the cell, one at each electrode. These are called half-reactions. The reaction at the anode is an oxidation reaction that releases electrons. Those electrons then flow through a wire to the cathode, where a reduction reaction takes place.
• Summary for Galvanic cell?


  Summary • An electrochemical cell is a device that produces an electric current as a result of an electron transfer reaction • In an electrochemical cell oxidation occurs at the anode and reduction occurs at the cathode. • A salt bridge is necessary to complete the circuit of an electrochemical cell. Anions flow towards the anode, cations flow towards the cathode. • Inert electrodes can be used when reactants and products can’t serve as the electrode material
• Electrochemical cell potentials?


  A cell reaction will be spontaneous (favourable) if the overall cell potential (E) is positive. if its negative its non-spondaneous.
• The total voltage of a cell can be calculated using the formula?

  Eo cell = Eo cathode - Eo anode
• Does Oxidation and reduction must occur together? Yes, In other words, an oxidation cannot occur without a simultaneous reduction, and vice versa. This is because one substance has to release electrons, which have to be taken up by another substance. • No absolute oxidising or reducing agents actually exist. In fact, the oxidising or reducing ability of a substance is a function of the reaction partner to be oxidised or reduced, respectively.
• Standard reduction potential?


  For a reaction to be spontaneous, the half reaction for the cathode (reduction) must be higher than the half reaction for the anode (oxidation) on the Table of Standard Reduction Potentials
• What are the steps in Balancing redox equations in acidic solutions?

  1. Identify reactants and products for each half-reaction 2. Balance atoms other than H and O 3. Balance oxygen by adding H2O 4. Balance hydrogen by adding H+. 5. Balance net charge by adding e-6. Make e- gain equal e- loss
• What are the steps for Balancing redox equations in basic solution? • Complete steps 1-6 as before. Then: 7. Take note of the number of H+ in the balanced equation and add the same number of OH-to each side 8. Combine H+ and OH- to form H2O 9. Cancel any H2O molecules that occur on both sides
• What is Corrosion?


   is a natural process that converts a refined metal into a more chemically stable oxide. 
• What is the process of Rusting? is the process where we have our steel

  the iron in our steel oxidising from oxygen in the air and we end up with a iron oxide which is rust.

   
• Corrosion Prevention Techniques: Galvanization

  • Process: Coating iron objects with zinc.
  • How it works:
  • Zinc corrodes instead of iron.
  • This protective action is called passivation.

  Cathodic Protection

  • Process: Using magnesium as a sacrificial anode.
  • How it works:
  • Magnesium corrodes instead of iron.
  • Commonly used for protecting large structures like pipelines and ships.
• Electrolysis is a process where electricity causes a chemical reaction by passing through a molten ionic compound or an electrolyte solution.
• What are the key points?

  • DC Source: Acts as an electron pump, moving electrons between electrodes. This leads to..
  • Anode (Positive Electrode): Attracts negative ions (anions).
  • Cathode (Negative Electrode): Attracts positive ions (cations).
• Comparison of electrolytic and galvanic cells: In a galvanic cell, the cathode is positive and the anode is negative. – In an electrolytic cell, the cathode is negative and the anode is positive.
• simple definition of Electrolysis: provide energy to make a reaction non spontaneous to occur
• What is Galvanic Protection?


  • Concept: Using a more reactive metal to protect another metal.
  • How it Works: The more reactive metal corrodes first, protecting the less reactive metal.
• What is Passivation?

  • Some metals form a protective oxide layer on their surface when exposed to air.
  • Effect: This oxide layer prevents further corrosion by acting as a barrier.
• Sacrificial Anode:

  • Purpose: Protect large structures like bridges or boats from corrosion.
  • Method: Attach a more reactive metal (like zinc) as an anode.
  • Benefits:
  • No need to coat the entire surface.
  • Easier to replace the anode than reapply a coating.
  • Common Practice: Using a lump of zinc as the sacrificial anode.
• Batteries • In batteries, a group of galvanic cells are connected in series so that the potentials of the individual cells add up. • Primary cells are cells not designed to be recharged. • Secondary cells are cells designed for repeated use.
• To find the spontaneous reaction:

  cathode needs to be above the anode
• To find the non-spontaneous reaction: cathode is below the anode.