1. Chem2_BeCsLi_Q1: REDOX
TERMS
 Reduction-Oxidation Reaction (REDOX): chemical reaction involving electron transfer
 Reduction: half reaction where electrons are gained
 Oxidation: half reaction where electrons are lost
 Oxidant/ Oxidizing Agent (OA): undergoes reduction to oxidize its partner
 Reductant/ Reducing Agent (RA): undergoes oxidation to reduce its partner
✔ GEROA Gain Electron -> Reduction -> Oxidizing Agent
✔ LEORA Lose Electron -> Oxidation -> Reducing Agent
 Oxidation State/ Number (O.N.): number of electrons equal to the magnitude of charge
of an atom would have if its shared electrons were held completely by the atom that
attracts them more strongly
RULES IN ASSIGNING O.N.
1. for free elements (Na, O2, Zn, Cl2, etc.) ON = ZERO
2. for monoatomic ions ON = charge
3. for Group 1A ON = +1
4. for group 2A ON = +2
5. for oxygen ON = -2 except for peroxide (O22-) ON = -1
6. for hydrogen ON = +1 except for hydride (H-) ON = -1
7. for fluorine ON = -1 , for Cl, Br, and I, ON varies (i.e. Oxyanions)
8. for neutral molecules sum of O.N. of all atoms = ZERO
H2O: 2(+1) + 1(-2) = 0
9. for polyatomic ion sum of O.N. of all atoms = NET CHARGE
NH4+: 1(-3) + 4(+1) = +1
10. O.N. may be fractions (i.e. S4O62-)
4(+5/2) + 6(-2) = -2
Exercises: Find the O.N. of the element in the compound
1. S in sodium sulfite 6. S in S8
2. Mn in potassium permanganate 7. Cr in Na2CrO4
3. N in calcium nitrate 8. V in K3V5O14
4. N in nitrogen dioxide 9. C in C2H6O
5. S in hydrogen thiosulfate 10. P in P2O74-
When is a given reaction considered a REDOX reaction? IF THERE IS CHANGE IN O.N.
a. combination 0 0 +1 -1
2 K + Cl2 2 KCl
b. decomposition +2 -2 0 0
2 HgO 2 Hg + O2
c. single displacement 0 +1 -2 +1 -2+1 0
2 Li + 2 H2O 2 LiOH + H2
d. combustion -4 +1 0 +4 -2 +1 -2
CH4 + 2 O2 CO2 + 2 H2O
e. double displacement +1+5-2 +1 -1 +1 -1 +1+5-2
AgNO3 + NaCl AgCl + NaNO3 NO CHANGE IN O.N. : DD = REDOX
Exercises: Which reactions are REDOX? If REDOX, identify the RA and OA for each reaction.
1. S2O3-2 + I2 S4O6-2 + I-
2. KCl + H2SO4 KHSO4 + HCl
3. H2O2 + PbS PbSO4 + H2O