Redox and electrode potentials

• Oxidising agent


  a substance that oxidises another atom or ion by causing it to lose electrons, gets reduced
• Reducing agent


  a substance that reduces another atom or ion by causing it to gain electrons, gets oxidised
• Redox titration


  A titration where an oxidising agent is titrated against a reducing agent, there is a transfer of electrons
• What acid is used in a Potassium manganate(VII) titration?

  dilute sulfuric acid as it does not oxidise in these conditions and does not react with the manganate(VII) ions
• Why cant hydrochloric acid be used in the potassium manganate(VII) titration?

  As it can be oxidised to chlorine by the manganate(VII) ions
• Why cant nitric acid be used in the potassium manganate(VII) titration?

  As it is an oxidising agent so may oxidise the substance
• Why can't ethanoic acid be used in the potassium manganate(VII) titration?

  As it is a weak acid so [H+] is insufficient
• Why cant concentrated sulfuric acid be used in the potassium manganate(VII) titration?

  As it may oxidise the substance being analysed
• Colour of the manganese(II) ions, Mn^2+(aq)

  very pale pink, looks colourless
• colour change for the potassium manganate(VII) titration

  colourless to pale pink- due to an excess of Mn^7+(aq)
• What affects the electrode potential

  Temperature, Pressure of gases, Concentration of reagents
• Standard conditions for comparing electrode potentials

  Ion concentration of 1.00 moldm^-3 298K 100kPa
• standard electrode potential


  the potential difference produces when a standard half-cell is connected to a standard hydrogen cell under standard conditions
• standard hydrogen electrode half-cell

  used as a reference, made of hydrogen gas in equilibrium with 1.00 moldm^-3 H+an inert platinum electrode which is in contact with the hydrogen gas and h+ ions
• Types of different types of half-cells that can be connected to a standard hydrogen electrode

  -A metal/metal ion half-cell

  -A non-metal / non-metal ion half-cell

  -An ion/ion half-cell (ions in different oxidation states)
• Benefit to fuel cells

  -Environmentally friendly as water is the only product

  -Efficient energy conversion as bond energy is converted into electrical energy without combustion

  -No harmful nitrogen oxides produced
• What does a fuel cell consist of?

  -a reaction chamber with seperate inlets for hydrogen and oxygen gas

  -an outlet for the product -water

  -an electrolyte of aqueous NaOH

  -a semi-permeable membrane that seperates the H2 and O2 gases
• Risks of fuel cells

  Hydrogen is very flammable-thick walled cylinders needed to store hydrogen

  -expensive

  -relies on a non-renewable finite resource

  -lots needed as hydrogen has a low density due to being a gas