Chemsitry: Redox Equations Flashcards
When is a redox equation balanced?
-numbers of atoms of each element on both sides are the same
-total charge same on both sides
What steps do you take in order to balance an unbalanced redox equation?
-write oxidation states above each element
-identify species oxidised and reduced
-determine amount of electrons gained/lost
-balance number of electrons gained/lost
-balance remaining atoms
Using the unbalanced equation, MnO4- + Fe2+ + H+ -> Mn2+ + Fe3+ + H2O, show the steps involved to balance this redox equation?
- oxidation states above each species
Mn: +7 O4: -2 Fe: +2 H: +1 -> Mn: +2 Fe: +3 H: +1 O: -2 - identify species oxidised and reduced
Mn: +7 -> Mn:+2 reduction, gain 5e-
Fe: +2 -> +3 oxidation, loss 1e- - balance number of electrons transferred
MnO4- + 5e- -> Mn2+
Fe2+ -> Fe3+ + e-
therefore multiple by 5
MnO4- + 5Fe2+ + H+ -> Mn2+ + 5Fe3+ + H2O - balance all other elements involved
MnO4- + 5Fe2+ + 8H+ -> Mn2+ + 5Fe3+ + 4H2O
What happen in a disproportionation reaction?
atoms of same element both reduced and oxidised
If an element has been oxidised, on what side are the electrons added in a half equation?
side of products
If an element has been reduced, what side are the electrons added to?
side with reactants
How do you find the number of electrons transferred from oxidation states?
the difference between oxidation states
If the oxidation state increases, has it been oxidised or reduced?
oxidised
If the oxidation state decreases, has the element been oxidised or reduced?
reduced
Using the example, 3Cu + 8H+ + 2NO3 -> 3Cu2+ + 2NO + H2O, show how you would find the half equations
Cu: 0 H+: +1 N: +5 O: -2 -> Cu: 2+ N: +2 O: -2 H:+1 O: -2
3Cu -> 3Cu2+ Cu: increase by +2 3Cu: 2x3 = 6 6 electrons transferred
3Cu -> 3Cu2+ + 6e-
2NO3- -> 2NO N: increase by +3 2N: 3x2=6 6 electrons transferred
2NO3- + 6e- -> 2NO
however oxygen molecules not accounted for, add H+ to reactants and H2O to products
2NO3- + 8H+ + 6e- -> 2NO + 4H2O