redox

• define oxidation


  loss of electrons

  loss of hydrogen

  gain of oxygen
• define reduction

  gain of electrons

  gain of hydrogen

  loss of oxygen
• define redox

  reduction and oxidation within the same reaction
• define oxidising agent


  a reactant which is an electron acceptor (it itself is reduced)
• define reducing agent


  a reactant which is an electron donor (it itself is oxidised)
• define oxidation state


  the extent to which an element has been oxidised. oxidation refers to the process in which the oxidation state of an element increases and reduction refers to a process in which the oxidation state of an element decreases
• define disproportionation

  oxidation and reduction of the same element in the same reaction
• define molecular ions


  two or more atoms covalently bonded with an overall charge
• what is the rules for writing ionic equations

  water soluble ionic compounds split into their ions

  acids split in water (ionize)

  insoluble ionic compounds dont split in water

  covalent compounds dont split
• what should you check in ionic equations

  check atoms are balanced on both sides

  check charges are balanced on both sides
• what is a precipitation reaction

  when 2 clear solutions are mixed and a cloudy solid forms

  the solid is called a precipitate
• what is the solubility of salts in water to form aqueous solutions

  K+, Na+, NH4+ salts = soluble

  nitrates = soluble

  sulfates = soluble EXCEPT barium and lead

  halides = soluble EXCEPT silver and lead

  carbonates = insoluble EXCEPT K+, Na+, NH4+
• what in MnO4-

  maganate (VII)
• what is KMnO4

  potassium maganate (VII)
• what colour is KMnO4

  purple solution
• what is Cr2O72-

  dichromate (VI)
• what is KCr2O7

  potassium dichromate (VI)
• what colour is potassium dichromate

  orange solution
• what are spectator ions

  ions that do not partake / change in the reaction
• what are common spectator ions

  group one metals, nitrates and sulfates
• write the ionic equation of neutralisation

  HO- (aq) + H+ (aq) -> H2O (l)
• what is the method for writing half equations

  write down formula of reactants and products

  balance number of atoms except oxygen and hydrogen

  add water molecules to opposite side to balance oxygens

  add H+ ions to other side to balance hydrogens

  balance total charges by adding e- to more + side
• oxidation in terms of oxidation number

  process in which the oxidation state of an element increases
• reduction in terms of oxidation number


  process in which the oxidation state of an element decreases
• metal elements are

  reducing agents
• non metal elements are

  oxidising agents
• what is the oxidation number of elements

  metals = 0

  non metals = 0
• what is the oxidation state of ionic compounds

  simple monatomic ions = charge

  transition metals = need to be calculated

  charge on molecular ion = sum of oxidation numbers of elements in a species
• what is the oxidation state of covalent compounds

  atoms with a high electronegativity will be asigned a more negative oxidation state

  covalent compounds where one atom is more electronegative than another, the more electronegative element will have a negative oxidation number
• what is the oxidation state or oxygen and when is it not

  -2

  -1 in H2O2

  +2 in F2O (fluorine is more electronegative)
• what is the oxidation state of hydrogen and when is it not

  +1

  -1 in metal hydrides
• what does the sum of oxidation numbers =

  overall charge
• what are common reducing agents

  dichromate (VI) in acid

  maganate (VII) in acid

  oxygen

  chlorine

  iodine
• what are common oxidising agents

  iron salts

  thiosulfate
• explain using oxidation numbers why this is a redox reaction

  Cl2 + 2Br- -> 2Cl- + Br2


  the chlorine with oxidation number 0 in Cl2 has decreased to -1 in Cl- and is therefore being reduced. chlorine is acting as an oxidising agent (a reactant which is itself being reduced)

  the bromine in Br- with oxidation number -1 has increased to 0 in Br2 and is therefore being oxidised. bromine is acting as a reducing agent (a reactant which is itself being oxidised)
• what are the steps for writing half equations


  balance

  assign oxidation numbers

  get rid of spectator ions

  separate and add e- to balance charges
• what are the steps for writing half equations in acidic conditions

  write formula and balance atoms except oxygen and hydrogen

  add water molecules to balance oxygen

  add hydrogen ions (H+) to balance hydrogen

  work out total charge on both sides and add e- to balance
• what are the steps for writing half equations in alkaline conditions

  write formula and balance atoms except oxygen and hydrogen

  add hydrogen ions (H+) to react with any oxygen atoms to form sufficient water molecules

  balance oxygen by adding H2O to side deficient

  in basic solution, follow this step by neutralising the H+ - do this by adding an equivalent amount of OH- to both sides of the equation

  form water on the side with H+ and OH- (H+ + OH- -> H2O)

  simpify water by subtracting H2O from both sides

  work out total charge and balance using e-
• what is the method for writing redox reactions from half equations

  write the 2 half equations

  multiply one equation so the amount of electrons is equal on both sides, if needed

  add the 2 equations together

  cancel the electrons and any other species which appear on both sides of the equation
• explain why this is a disproportionation reaction

  Cl2 + 2NaOH -> NaCl + NaClO + H2O


  chlorine in Cl2 with oxidation number 0 is increasing and being oxidised to +1 in NaClO, while simultaneously decreasing and being reduced to -1 in NaCl, within the one reaction