Redox

• What is oxidation?

  • The loss of electrons
  • OR Gain of Oxygen (or any electronegative element)
  • OR Loss of Hydrogen (or any electropositive element)
• Reduction: The process of electron gain / decrease in oxidation number
• Define oxidation state. A number which represents the number of electrons lost or gained by an atom of that element in the compound
• Oxidising agent: A reagent that oxidises (removes electrons from) from another species.
• Reducing agent: a species that reduces another element (electron donors)
• What is reduction?

  • The gain of electrons
  • OR Loss of Oxygen (or any electronegative element)
  • OR Gain of Hydrogen (or any electropositive element)
• What are the half equations for SnO + Zn → ZnO + Sn?Half Equations:

  • Sn2+ + 2e- → Sn
  • Zn → Zn2+ + 2e
• What is the oxidation state of oxygen in OF2 ? [O] = +2
• What is the oxidation state of hydrogen in KH ? [H] = -1
• What is the oxidation state of chlorine in NaClO ?[Cl] = +1
• Disproportionation: Where in a redox reaction, the oxidation states of atoms of the same element, increase for some atoms, whereas decrease for some atoms.
• In disproportionation reactions, there will be two different species with the same element that have different oxidation numbers.
• What is the oxidation state of phosphorus in PCl5 ? [P] = +5
• What is the oxidation state of nitrogen in ammonia? [N] = -3
• What is the oxidation state of arsenic in AsO4 -3 ?[As] = +5
• What happens in a redox reaction:

  • Electrons are transferred from one species (element) to another.
  • One element is oxidised whilst another is reduced.
• Why is, 2CrO4 2- + 2H+ → Cr2O7 2- + H2O, not a redox reaction? Chromium is oxidised whereas hydrogen remains the same oxidation state (no element is reduced).
• All acids contain an element of hydrogen
• Acid + water --dissociates--> H+ ion + anion
• HCL -> Hydrochloric acid

  H2SO4 -> Sulfuric acid

  HNO3 -> Nitric acid

  CH3COOH -> Ethanoic acid
• HCL -> H+ + CL-
• H2SO4 -> H+ + SO4^2-
• HNO3 -> H+ + NO3-
• CH3COOH -> H+ + CHCOO-
• Bases are metal oxides, metal hydroxides, metal carbonates
• Bases can neutralise an acid to produce a salt

  Base + acid = salt
• fill in the blank

  A) replaced hydrogen ions

  B) oxygen and hydrogen ions form water

  C) metal carbonate

  D) acid

  E) salt

  F) carbon dioxide

  G) water

  
• Alkali's are bases that dissolve in water

  CuO -> insoluble in water -> base only.

  NaOH -> soluble in water -> base + alkali (sodium hydroxide solution)
• all group 1 metal hydroxides are soluble in water

  therefore, can form Alkali's
• Key features of Alkali's

  • In solution = release hydroxide ion (OH-)
  • Alkali + acid = salt + water
• A redox reaction is when both reduction and oxidisation has taken place. it can be written as half-equations.
• Rules of oxidation numbers:

  1. All elements have an oxidation number of 0
  2. Oxidation states of the atoms in a molecule add up to 0
  3. Oxidation states of an ion is the same as its charge
• Rules of oxidation numbers:

  Group 1 = +1

  Group 2 = +2

  Group 3 = +3

  Fluorine = -1

  Hydrogen = +1

  Oxygen = -2

  Chlorine = -1

  Unless it is combined with something above (switches)
• some elements have multiple oxidation states (usually transition metals)

  if they do, the value is given in the name
• fill in the blank

  A) nothing changed, no oxidisation or reduction

  B) calcium was oxidised, hydrogen reduced, SO4 spectator

  
• a disproportionation is when the substance is both oxidised and reduced to give two different products.
• Example of disproportionation reaction is cold aqueous NaOH and hot concentrated NaOH
• cold aqueous NaOH

  2 NaOH -> CL2 -> NaCL + NaCLO + H2O
• hot concentrated NaOH

  3 CL2 + 6 NaOH -> 5 NaCL + NaCLO3 + 3 H2O
• Half equation steps:

  1. Redox reaction? oxidation numbers? oxidised or reduced?
  2. Construct half equations for the chemicals that has been oxidised/reduced
  3. create full ionic equation from half equations = balance e-
  4. assemble the ionic equation (left remains left and right remains right) 'leaving out spectator ions'
  5. replace numbers into original equation