PMT flashcards chapter 23

• What is an oxidising agent?

  A species that is reduced in a reaction
• How does an oxidising agent function in a reaction?

  It causes another species to be oxidised
• What is a reducing agent?

  A species that is oxidised in a reaction
• What role does a reducing agent play in a reaction?

  It causes another species to be reduced
• What is oxidation defined as?

  Loss of electrons
• What does an increase in oxidation number indicate?

  Oxidation has occurred
• What is reduction defined as?

  Gain of electrons
• What does a decrease in oxidation number signify?

  Reduction has occurred
• What occurs in a redox reaction?

  Electrons are transferred between species
• What happens to one element in a redox reaction?

  One element is oxidised while another is reduced
• Why is the reaction 2CrO4^2- + 2H⁺ → Cr₂O₇^2- + H₂O not a redox reaction?

  Hydrogen remains the same oxidation state
• What are the half equations and ionic equation for SnO + Zn → ZnO + Sn?

  Half Equations:

  • Sn²⁺ + 2e^- → Sn
  • Zn → Zn²⁺ + 2e^-

  
  

  Ionic Equation:

  • Sn²⁺ + Zn → Sn + Zn²⁺
• What is the definition of standard electrode potential?

  e.m.f. of a half cell compared to hydrogen
• Under what conditions is standard electrode potential measured?

  At 298 K, 1 mol dm^-3, 100 kPa
• What happens when a rod of metal is dipped into a solution of its own ions?

  An equilibrium is set up between metal and ions
• What is the half-equation for zinc (s) to zinc (II)?

  Zn (s) ⇌ Zn²⁺(aq) + 2e^-
• What is the half-equation for copper (II) to copper (III)?

  Cu²⁺(aq) ⇌ Cu³⁺(aq) + e^-
• What are the components of a standard hydrogen half cell?

  • Hydrochloric acid 1 mol dm^-3
  • Hydrogen gas at 100 kPa
  • Inert platinum electrode
• Why is the hydrogen half cell used as a standard half cell?

  It is easy to control its purity and reproducibility
• How do you make a simple salt bridge?

  Soak filter paper in KNO₃ or NH₄NO₃
• Why are salt bridges necessary in electrochemical cells?

  They complete the circuit and enable charge transfer
• Why might you use other standard electrodes occasionally?

  • Cheaper and easier to use
  • Quicker to set up
  • Provide good reference
  • Platinum is expensive
• What does a more negative E_o value indicate about reducing power?

  Better reducing agent, easier to oxidise
• What does a more positive E_o value indicate about oxidising power?

  Better oxidising agent, easier to reduce
• How do you calculate the emf of a cell from E_o values?

  E_o cell = E_o positive - E_o negative
• When would you use a platinum electrode?

  When both forms of metal are in solution
• Why is platinum chosen for electrodes?

  It is inert and a good conductor
• How would you predict if a reaction would occur?

  By comparing standard electrode potentials
• How do you calculate the emf of a cell from Eo values?

  $Eo_{cell} =$$Eo_{positive} - Eo_{negative}$
• When would you use a Platinum electrode?

  When both oxidised and reduced forms are in solution
• Why is Platinum chosen as an electrode material?

  It is inert and a good conductor
• How would you predict if a reaction would occur?

  Calculate Eo value of reduced minus oxidised
• What indicates that a reaction will occur based on Eo values?

  If Eo overall > 0.4V, reaction occurs
• What are the 3 main types of electrochemical cells?

  • Non rechargeable cells
  • Rechargeable cells
  • Fuel cells
• How do non rechargeable cells work?

  They provide energy until chemicals are exhausted
• How do rechargeable cells work?

  Reactions can be reversed when recharging
• Why is lithium used in laptop batteries?

  It has low density and is very reactive
• What are the drawbacks of using lithium batteries?

  • Toxic if ingested
  • Rapid discharge can cause fire or explosions
• How do fuel cells work?

  They use external supplies of fuel and oxidant
• What are the modern fuels used in fuel cells?

  • Hydrogen
  • Hydrogen rich fuels (e.g., methanol)