Redox Reactions. :Redox Reactions. Oxidation Reduction Visit www.worldofteaching.com For 100’s of free powerpoints This Powerpoint is hosted on www.worldofteaching.com Please visit for 100’s more free powerpoints


GCSE :GCSE Oxidation: Gain of oxygen Loss of electrons Reduction: Loss of oxygen Gain of electrons Increase in oxidation number Decrease in oxidation number


4 Experiments: :4 Experiments: Burning magnesium Copper in silver nitrate solution Chlorine solution and potassium iodide solution Exploding hydrogen Word equation Balanced symbol equation


2Mg(s) + O2(g) ? 2MgO(s) :2Mg(s) + O2(g) ? 2MgO(s) Oxidised – gains oxygen Must be a redox! Mg ? Mg2+ O ? O2- Put the e- in. +2e- +2e- Oxidised – loss of e- Reduced – gain of e-


Cu(s) + 2AgNO3(aq) ? Cu(NO3 )2(aq) + 2Ag(s) :Cu(s) + 2AgNO3(aq) ? Cu(NO3 )2(aq) + 2Ag(s) Ag+ ? Ag Cu ? Cu2+ Complete the half-equations +e- +2e- Oxidised? Reduced? Oxidised – loss of e- Reduced – gain of e-


Try Question 1. :Try Question 1.


H2(g) + ½ O2(g) ? H2O(g) :H2(g) + ½ O2(g) ? H2O(g) Covalent! No H+ or OH- Need a new definition.


GCSE :GCSE Oxidation: Gain of oxygen Loss of electrons Reduction: Loss of oxygen Gain of electrons Increase in oxidation number Decrease in oxidation number


Oxidation Numbers :Oxidation Numbers The oxidation number of an atom in an element is zero. E.g. Mg in Mg, O in O2.


Oxidation Numbers :Oxidation Numbers The oxidation numbers of atoms in a compound add up to zero. Oxidation state of C in CO2? ? – 4 = 0 ? = +4 Put the +!


Oxidation Numbers :Oxidation Numbers The oxidation numbers of atoms in a compound add up to zero. Oxidation state of Mg in MgCl2? +2


Oxidation Numbers :Oxidation Numbers The oxidation numbers of atoms in a compound add up to zero. Oxidation state of N in NH3? -3


Oxidation Numbers :Oxidation Numbers The oxidation numbers of atoms in an ion add up to the charge on the ion. Oxidation state of S in SO42-? ? – 8 = -2 ? = +6


Oxidation Numbers :Oxidation Numbers The oxidation numbers of atoms in an ion add up to the charge on the ion. Oxidation state of S in S2-? -2


Oxidation Numbers :Oxidation Numbers The oxidation numbers of atoms in an ion add up to the charge on the ion. Oxidation state of N in NH4+? -3


Try Question 2. :Try Question 2.


H2(g) + ½ O2(g) ? H2O(g) :H2(g) + ½ O2(g) ? H2O(g) Covalent! No H+ or OH- Need a new definition.


GCSE :GCSE Oxidation: Gain of oxygen Loss of electrons Reduction: Loss of oxygen Gain of electrons Increase in oxidation number Decrease in oxidation number


H2(g) + ½ O2(g) ? H2O(g) :H2(g) + ½ O2(g) ? H2O(g) Covalent! No H+ or OH- Need a new definition. +1 0 -2 0 O H


H2(g) + ½ O2(g) ? H2O(g) :H2(g) + ½ O2(g) ? H2O(g) +1 0 -2 0 O H Oxidised? H – increase in oxidation number Reduced? O – decrease in oxidation number


Try Question 3. :Try Question 3.


Oxidation Numbers and names :Oxidation Numbers and names To avoid any confusion when an element can have several oxidation numbers, the oxidation number is usually mentioned in the compound’s name. In names like “elementate(X)”, the number refers to “element” and not the associated oxygens. So if we look at some examples , we get the following names:- KMnO4 potassium manganate(VII) NaClO3 sodium chlorate(V) POCl2F phosphorus(V) oxydichlorofluoride NaH2PO3 sodium dihydrogenphosphate(III) K2Cr2O7 potassium dichromate(VI) Check the numbers.


Try any 3 in Question 7. :Try any 3 in Question 7.


Slide 24:Well done!