Chemistry form 5

Subdecks (2)

Cards (676)

  • Redox reactions
    Chemical reactions involving oxidation and reduction occurring simultaneously
  • Aspects to understand Redox reactions
    • Losing or gaining oxygen
    • Losing or gaining hydrogen
    • Changing of oxidation number
    • Transferring of electron
  • Redox in terms of Oxygen transfer
    1. Oxidation is gain of oxygen
    2. Reduction is loss of oxygen
  • Redox in terms of Oxygen transfer
    • In the extraction of iron from its ore: Fe2O3 + 3CO → 2Fe + 3CO2
  • When a substance gains oxygen
    It is said to be oxidised (undergoes oxidation)
  • When a substance loses oxygen
    It is said to be reduced (undergoes reduction)
  • Oxidising Agents and Reducing agent
    1. The substance that causes oxidation is called oxidising agent (a substance which oxidises something else)
    2. The substance that causes reduction is called reducing agent (a substance which reduces something else)
  • Redox in terms of Hydrogen transfer
    1. Oxidation is loss of hydrogen
    2. Reduction is gain of hydrogen
  • Redox in terms of Hydrogen transfer
    • Ammonia can be oxidised to form nitrogen gas: 2NH3(g) + 3Br2 → N2(g) + 6HBr(g)
  • The substance that causes oxidation is called oxidising agent (a substance which oxidises something else)
  • The substance that causes reduction is called reducing agent (a substance which reduces something else)
  • Oxidising agents give oxygen to another substance or remove hydrogen from it
  • Reducing agents remove oxygen from another substance or give hydrogen to it
  • Example of oxidising agent
    • potassium permanganate (KMnO4), Hydrogen peroxide (H2O2), chlorine water (Cl2), concentrated nitric acid
  • Example of reducing agent
    • active metals such as sodium, magnesium, sulphur dioxide (SO2), hydrogen sulphide (H2S)
  • Examples of oxidation and reduction reactions
    • Zn is oxidised to ZnO
    • PbO is reduced to Pb
    • Mg is oxidised to MgO
    • H2O is reduced to H2
    • H2S is oxidised to S
    • Cl2 is reduced to HCl
  • REDOX in terms of Electron transfer
    1. Oxidation occurs when a reactant loses electron
    2. Reduction occurs when a reactant gains electron
  • In the reaction CuO(s) + Mg(s) → Cu(s) + MgO(s), Magnesium metal loses 2 electrons to form magnesium ions
  • In the reaction Cu2+ + 2e- → Cu, Copper gains 2 electrons to form copper metal
  • This is an oxidation reaction
  • This is a reduction reaction
  • In the ionic equation CuO(s) + Mg(g) → Cu(s) + MgO(s), the oxidising agent is CuO and the reducing agent is Mg
  • In the reaction 2Na(s) + Cl2(g) → 2NaCl(s), sodium atom loses 1 electron to form a sodium ion
  • In the reaction Na+Cl- each molecule of chlorine accepts 2 electrons to form 2 chloride ions
  • Oxidation occurs when a reactant loses an electron
  • Reduction occurs when a reactant gains an electron
  • In this reaction, sodium atom loses 1 electron to form a sodium ion
  • In this reaction, each molecule of chlorine accepts 2 electrons to form 2 chloride ions
  • Marginal utility
    The additional utility (satisfaction) gained from the consumption of an additional product
  • If you add up marginal utility for each unit, you get total utility
  • Oxidation state shows the total number of electrons which have been removed from an element (positive oxidation state) or added to an element (negative oxidation state) to get to its present state
  • All elemental state has an oxidation number of 0
  • Potassium in its elemental state has an oxidation number of 0, but when it loses an electron, its oxidation state is +1
  • Oxidation numbers of various compounds
    • Fe2O3: +3
    • CuCl: +1
    • CuCl2: +2
    • PbO: +2
    • PbO2: +4
    • MnO: +2
    • Mn2O3: +3
    • MnO2: +4
  • Systematic names and traditional names of compounds
    • KMnO4: Potassium manganate(VII), Potassium permanganate
    • K2CrO4: Potassium chromate(VI), Potassium chromate
    • HNO2: Nitric(III) acid, Nitrous acid
    • HNO3: Nitric(IV) acid, Nitric acid
  • Elements that have only 1 oxidation number such as Group 1, 2, 13, their oxidation number are not included in their names
  • Redox reactions involve oxidation and reduction occurring simultaneously
  • Aspects to understand Redox reactions
    • Losing or gaining oxygen
    • Losing or gaining hydrogen
    • Changing of oxidation number
    • Transferring of electron
  • Definition of Oxidation and Reduction
    Oxidation is increase in oxidation number, Reduction is decrease in oxidation number
  • Example of Redox reaction with Zinc and Oxygen
    0 → +2, O2 → O2−