14: Redox II

• How is a voltage generated in electrochemical cells?

  Due to the electron transfer in a redox reaction
• What is a salt bridge in an electrochemical cell?

  A tube of unreactive ions that can move between the solutions (electrolytes) to carry the flow of charge
• In an electrochemical cell, what chemical is most often used for the salt bridge?

  Potassium nitrate
• In an electrochemical cell, where does oxidation occur?

  At the anode
• In an electrochemical cell, where does reduction occur?

  At the cathode
• In an electrochemical cell, at the cathode, does oxidation or reduction occur?

  Reduction
• In an electrochemical cell, at the anode, does oxidation or reduction occur?

  Oxidation
• In an electrochemical cell, is the cathode negative or positive?

  Positive
• In an electrochemical cell, is the anode negative or positive?

  Negative
• How many half-cells make up an electrochemical cell?

  Two
• What is required to make a half cell?

  An electrode and electrolyte
• Give the three possible types of half cell?

  Metals in contact with a solution of their ions, solutions of ions in two different oxidation states & gases in contact with a solution of their ions
• How is the electrode potential of a single-half cell measured?

  Relative to a standard hydrogen electrode
• What is the name of the half-cell used as the reference half-cell?

  Standard hydrogen electrode
• What are standard conditions?

  298K, 100kPa & 1 mol per dm cubed
• What is the potential of a standard hydrogen electrode (note it is the reference cell)?

  0V
• What conditions are required to set up a standard hydrogen electrode?

  298K, 100kPa & 1 mol per dm cubed
• What electrode is used in a standard hydrogen electrode?

  Platinum
• What electrode is used for a half-cell made up of two different solutions of ions of the same element but in different oxidation states?

  Platinum
• What is used to give the voltage reading of an electrochemical cell?

  High-resistance voltmeter
• When two half-cells are combined to make an electrochemical cell, which half equation will be the one being reduced?

  The one with a more positive standard electrode potential
• Is the half equation with the less positive standard electrode potential likely to to be reduced or oxidised?

  Oxidised
• When combining half equations (to make full electrochemical equation), if you have to multiply an equation by a set number so the electrons in either equation are balanced, do you also multiply the standard electrode potential value?

  No
• How do you calculate the emf value of an electrochemical cell?

  Combine the two standard electrode potential values. If one half equation has been flipped to show oxidation (so the value also flipped) then the two should be added. If nothing has been flipped then just do more positive value minus more negative value
• When is a reaction thermodynamically feasible?

  When the emf value is positive
• What is the emf value directly proportional to?

  ln(k) & total entropy change
• Give the three main limitations of using emf values?

  Relies on conditions remaining standard, doesn't account for reaction kinetics, relies on equilibrium being established
• In a cell diagram, does the reduction or oxidation reaction go on the right?

  Reduction
• When looking at a cell diagram, is the reaction on the left the reduction or oxidation?

  Oxidation
• What is the easiest way to remember where to put reduction and oxidation equations in a cell diagram?

  The electrons essentially go in the middle
• What do two vertical lines together represent in a cell diagram?

  The salt bridge
• What must you always remember to add to a cell diagram (at the end of either equation)?

  Electrode
• If a solid isn't present in a half equation, what should be added when making a cell diagram?

  A platinum electrode
• Should state symbols be included in a cell diagram?

  Yes
• What goes inbetween reactants/products of the same phase in a cell diagram?

  Comma
• What does a singular vertical line do in a cell diagram?

  Seperate different phases
• When a half equation in a cell diagram features three or more reactant/products, what must be included?

  Suare brackets grouping reactants and products
• What are the three types of storage cell?

  Non-rechargable, rechargable & hydrogen
• Why is a Leclanche cell non-rechargable?

  The reaction is not reversible because the hydrogen produced is oxidised (by manganese dioxide) to water. The ammonia gas is then dissolved in this water
• What is required in order for a fuel cell to generate a constant voltage?

  Fuel (methanol or other hydrogen rich fuel) and air