Electrochemistry Flashcards
Electronegativity is…
A measure of the tendency of an atom (of that element) to attract a bonding pair of electrons
oxidation can be identified by…
- a loss of electrons
- an increase in oxidation number
- the gaining of oxygen
- the loss of hydrogen
reduction can be identified by…
- a gain of electrons
- a decrease in oxidation number
- the loss of oxygen
- the gain of hydrogen
redox reactions involve…
electron transfer
oxidation shows electrons on the ___ side of the equation
RHS (R cannot go with Reduction)
reduction reactions show electrons on the ___ side of the equation
LHS
oxidants or oxidising agents are…
reactants that cause another substance to be oxidised
reductants or reducing agents are…
reactants that cause another substance to be reduced
explain qs for oxidants
a reaction with (oxidant) causes (other reactant) to lose electrons. thus, it is causing the oxidation of (other reactant)
explain q for reducant
a reaction with (reductant) causes (other reactant) to gain electrons. thus, (reductant) is causing the reduction of (other reactant)
do oxidation numbers appear as: +2, -2 or 2+, 2-?
+2 or -2, always the sign preceding the number
rule one for oxidation numbers (N.O)
the sum of all the oxidation numbers in any substance is equal to the overall charge. this means that in elemental form, it will always have an N.O of 0.
eg. Oxygen gas = N.O of 0
Oxide ion (2-) = N.O of -2
rule two for oxidation numbers (N.O)
fluorine has an N.O of -1 in compounds
rule three for oxidation numbers (N.O)
group one metals are +1 in compounds, while group 2 metals are +2 in compounds
rule four for oxidation numbers (N.O)
when H is bonded to non-metals, it has an oxidation number of +1. When H is bonded to metals, it has an oxidation number of -1 (hydride ion)
rule five for oxidation numbers (N.O)
oxygen usually has an oxidation number of -2 in compounds. however, in peroxides, it has an oxidation number of -1.
eg. H2O2, BaO2
rules six and seven for oxidation numbers (N.O) - not NECESSARY
- Group seven elements are usually -1 in compounds (unless a higher rule contradicts this). if two or more group seven elements are present, the more ELECTRONEGATIVE one is -1. Fluorine is the most electronegative element.
- In the absence of other information, group 6 metals are USUALLY -2, group 5 non-metals are USUALLY -3 and group 3 metals are USUALLY +3. many transition metals have variable oxidation numbers so assign these last.
find the oxidation number for : oxygen gas (O₂) and ammonium sulphate ((NH₄)₂SO₄)
oxygen gas - overall sum = 0, thus the N.O is 0
- O = 0
ammonium sulphate - sulphate has a sum of -2, O is -2 so 4 x -2 = -8, making S +6 (-8+6=-2)
- ammonium has a sum of +1, H is +1 so 4 x +1 = 4, making N -3 (4+-3 =+1) - S = +6, O = -2, N = -3, H = +1
