Oxidation - Reduction RedOx

RedOx reactions Chemical reactions involving an electron transfer between atoms. Elements will change oxidation state from the reactant side to the product side.

Rules of assigning oxidation states If in doubt with + or - The higher e-neg will get the - ! Group 1 is +1 Group 2 is +2 Transition METALS are always positive! Fluorine is -1 H is +1 in covalent & -1 in binary ionic O is -2 except with F then O is +2, or in a peroxide then -1.

Cu(s) Zn(s) Cl2(g) O2(g) O3(g) C60(s) Ne(g) …and Elements that are not bonded to a different element have oxidation states of zero. Examples Cu(s) Zn(s) Cl2(g) O2(g) O3(g) C60(s) Ne(g)

H2S H2SO3 H2SO4 NOW More complicated . . . sulfur has a -2 oxidation state H2SO3 sulfur has a +4 oxidation state H2SO4 sulfur has a +6 oxidation state How? 

Assigning oxidation states to atoms in a polyatomic ion Oxidation states on individual atoms must equal the charge on the ion (S+6 O4-2 ) -8 +6 = -2 (S O4-2 ) -8 = -2 (S O4) = -2 (SO4)

Try these . . . hydroxide ammonium chromate

Try these answers. . . Hydroxide OH-1 O: -2 H: +1 ammonium NH4+1 N: -3 (b/c higher e-neg) H: +1 Chromate CrO4-2 Cr: +6 O: -2

Put it all together……. Assign oxidation states to each atom in the compound KClO3 MnCr2O7 K2PtCl6

Put it all together……. answers KClO3 K: +1 Cl: +5 O: -2 MnCr2O7 Mn: +2 Cr: +6 O:-2 K2PtCl6 K: +1 Pt: +4 Cl: -1

2Na + 2HOH 2NaOH + H2 Hydroxide polyatomic ion Recognizing RedOx If the oxidation state changes for any of the atoms it is considered a RedOx reaction 0 +1 -2 +1 +1 -2 +1 0 2Na + 2HOH 2NaOH + H2 Hydroxide polyatomic ion

Single Replacement Reactions are ALWAYS RedOX Double Replacement Reactions are NEVER RedOX

RedOx: Yes or NO? HCl + NaOH  HOH + NaCl Mg + 2HCl  MgCl2 + H2 MnO2 + 4HBr MnBr2 + Br2 + 2H2O

RedOx Definitions….

Metals tend to undergo oxidation +3 +2 +1 -1 -2 -3 Oxidation results in an increase in oxidation state Atoms that Lose e-lectrons undergo Oxidation Metals tend to undergo oxidation

Non-metals tend to undergo reduction +3 +2 +1 -1 -2 -3 Reduction results in a decrease in oxidation state Atoms which Gain e-lectrons undergo Reduction Non-metals tend to undergo reduction

GeR

oxidation and reduction In a RedOx reaction If one atom is being oxidized another must be reduced. In other words . . . oxidation and reduction always occur together

Assign oxidation states to each atom. Is this a RedOx reaction? Al + CuCl2 Cu + AlCl3 Assign oxidation states to each atom. Is this a RedOx reaction? What species is oxidized? Reduced? Write a balanced equation based on these reactants.

2Al + 3CuCl2  2AlCl3 + 3Cu Write a balanced equation based on these reactants. Is this a RedOx reaction? YES What species is oxidized? Al0 Reduced? Cu+2

Assign oxidation states to all atoms What species is oxidized? MnO2 + 4HCl  MnCl2 + Cl2 + 2H2O Assign oxidation states to all atoms What species is oxidized? How do you know? What species is reduced?

Oxidation state increases from -1 to 0 Cl-1 loses electrons MnO2 + 4HCl  MnCl2 + Cl2 + 2H2O What species is oxidized? Cl -1 How do you know? Oxidation state increases from -1 to 0 Cl-1 loses electrons What species is reduced? Mn+4 Oxidation state decreases from +4 to +2 Mn+4 loses electrons

RedOx Practice Losing e- oxidation Gain e- Reduction Remember . . . +4 +3 +2 +1 -1 -2 -3 -4 Losing e- oxidation Gain e- Reduction Remember . . .

Writing half-reactions A half reaction shows either oxidation or reduction of a RedOx reaction. The electrons being lost (oxidation) or gained (reduction) are also shown.

Oxidation half-reaction example Fe(s)  Fe+3(aq) + 3e- Fe0 gets oxidized electrons are lost products conservation of mass AND CHARGE charges on both sides equal each other

Reduction half-reaction example Sn+4 + 2e-  Sn+2 Sn+4 gets reduced electrons are gained reactants conservation of mass AND CHARGE charges on both sides equal each other

Practice KMnO4 + HCl  MnCl2 + KCl + Cl2 + H2O Assign oxidation states…. What species is oxidized? ½ rxn? What species is reduced? Where does the electron transfer take place?

Answers KMnO4 + HCl  MnCl2 + KCl + Cl2 + H2O What species is oxidized? Cl-1 ½ rxn? Cl-1  Cl0 + 1e- or 2Cl-  Cl20 + 2e- What species is reduced? Mn+7 ½ rxn? Mn+7 + 3e-  Mn+4 Where does the electron transfer take place? Cl- loses e- to Mn+7

The End I came . . . I saw . . . I RedOxed