OxidationReduction Topic 9 Review Book Oxidation Numbers Oxidation

Oxidation-Reduction Topic 9 Review Book

Oxidation Numbers • Oxidation is the loss of electrons; Reduction is the gain of electrons • Oxidation and reduction go together. Whenever a substance loses electrons and another substance gains electrons • Oxidation Numbers are a system that we can use to keep track of electron transfers

LEO says GER! Loss of Electrons = Oxidation Gain of Electrons = Reduction

Rules for Assigning Oxidation Numbers • Free elements are 0 • Ions have the charge indicated • Metals : Group 1 = +1; Group 2= +2 • Halogens in binary compounds are usually -1, in ternary compounds move on and go back to do the algebra • Hydrogen is +1 unless in binary compound with metal, then it is -1 • Oxygen is -2 unless in peroxide when it is -1 or with fluorine when it is +2

Practice Assigning Oxidation Numbers NO 2 N 2 O 5 HCl. O 3 HNO 3 Ca(NO 3)2 KMn. O 4

Practice Assigning Oxidation Numbers NO 2 N= +4, O = -2 N 2 O 5 N = +5, O = -2 HCl. O 3 H=+1, Cl=+5, O = -2 HNO 3 H=+1, N = +5, O = -2 Ca(NO 3)2 Ca=+2, N =+5, O= -2 KMn. O 4 K=+1, Mn=+7, O= -2

Practice Assigning Oxidation Numbers Ca. Cl 2 K 2 Cr 2 O 7 KH Na. HCO 3 H 2 O Mg. O

Practice Assigning Oxidation Numbers Ca. Cl 2 Ca = +2, Cl = -1 K 2 Cr 2 O 7 K=+1, Cr=+6, O=-2 KH K = +1, H= -1 Na. HCO 3 Na= +1, H= +1, C=+4, O= -2 H 2 O H= +1, O= -2 Mg. O Mg = +2, O = -2

Using Oxidation Numbers • Careful examination of the oxidation numbers of atoms in an equation allows us to determine what is oxidized and what is reduced in an oxidation-reduction reaction

Using Oxidation Numbers • An increase in the oxidation number indicates that an atom has lost electrons and therefore oxidized. • A decrease in the oxidation number indicates that an atom has gained electrons and therefore reduced • Example Mg + Zn. SO 4 Mg. SO 4 + Zn

Exercise For each of the following reactions find the element oxidized and the element reduced Cl 2 + KBr KCl + Br 2 Mg + HNO 3 Mg(NO 3)2 + NO 2 + H 2 O HNO 3 + I 2 HIO 3 + NO 2

Exercise For each of the following reactions find the element oxidized and the element reduced Cl 2 + KBr KCl + Br 2 Br increases from – 1 to 0 -- oxidized Cl decreases from 0 to – 1 -- Reduced K remains unchanged at +1

Exercise For each of the following reactions find the element oxidized and the element reduced Mg + HNO 3 Mg(NO 3)2 + NO 2 + H 2 O • Mg increases from 0 to +2. It is oxidized • Only N in nitric acid changes from +5 to +4. It is reduced

Exercise For each of the following reactions find the element oxidized and the element reduced HNO 3 + I 2 HIO 3 + NO 2 • • • N is reduced from +5 to +4. It is reduced I is increased from 0 to +5 It is oxidized The hydrogen and oxygen remain unchanged.

Balancing Redox Reactions There are several basic steps 1. Assign oxidation numbers to the species in the reaction 2. Find the substance oxidized and the substance reduced 3. Write half reactions for the oxidation and reduction 4. Balance the atoms that change in the half reaction 5. Determine the electrons transferred and balance the electrons between the half reactions 6. Check your work. Make sure that both the atoms and charges balance

Balancing Redox Equations 1 1. Assign oxidation numbers to the species in the reaction 2. Find the substance oxidized and the substance reduced 3. Write half reactions for the oxidation and reduction 4. Balance the atoms that change in the half reaction 5. Determine the electrons transferred and balance the electrons between the half reactions 6. Check your work. Make sure that both the atoms and charges balance *It may be helpful to balance the equation before starting the redox process • Zn + HCl Zn. Cl 2 + H 2

Balancing Redox Equations 2 1. Assign oxidation numbers to the species in the reaction 2. Find the substance oxidized and the substance reduced 3. Write half reactions for the oxidation and reduction 4. Balance the atoms that change in the half reaction 5. Determine the electrons transferred and balance the electrons between the half reactions 6. Check your work. Make sure that both the atoms and charges balance Mn. O 2 + HCl Mn. Cl 2 + H 2 O

Balance, Assign, ID, write ½ rxns for the following • 1. Mg + O 2 Mg. O • 2. KCl. O 3 KCl + O 2 • 3. HCl + O 2 H 2 O + Cl 2

Balance the following ionic equations • ____Cr +6 + ____ S ___ Cr +3 +____ S +4 • ____Sn 2+ + ____Hg+ 2 ___Sn+4 + ___Hg +1 • _____Cu + _____Ag+1 ___Cu+2 + ___Ag