Department of Chemistry CHEM1010 General Chemistry *********************************************** Instructor: Dr. Hong Zhang Foster Hall, Room 221 Tel:

CHEM1010/General Chemistry _________________________________________ Chapter 8. (L30)-Oxidation and Reduction Today’s Outline..Review of three views of oxidation and reduction..Oxidants and reductants..Oxygen and oxidizing agents (oxidants) Oxygen Other common oxidants

Chapter 8. (L30)-Oxidation and Reduction Oxidants and reductants Oxidation and reduction happen together (they are coupled). Example: CuO + H 2 = Cu + H 2 O Cu: +2 0Cu is reduced H: 0 +1 H is oxidized CuO oxidizes H 2, so CuO is the oxidant (oxidizing agent) H 2 reduces CuO, so H 2 is the reductant (reducing agent)

Chapter 8. (L30)-Oxidation and Reduction Oxidants and reductants Oxidation and reduction happen together (they are coupled). Example: C + O 2 = CO 2 C: 0 +4C is oxidized O: 0 -2 O is reduced O 2 oxidizes C, so O 2 is the oxidant (oxidizing agent) C reduces O 2, C is the reductant (reducing agent)

Chapter 8. (L30)-Oxidation and Reduction Oxygen: An abundant and essential oxidizing agents (oxidants)..Oxygen is the most common oxidant...Oxygen is essential to life (respiration; generating energy)..Human body: 65% of body is water by mass, 89% of water is oxygen by mass..21% of air by volume is oxygen..Combustion: burning with oxygen, oxidation..Pure oxygen can be made by liquefying air..~20 billion kg of oxygen is produced per year in USA..Oxygen can also cause food spoilage, wood decay, and corrosion.

Chapter 8. (L30)-Oxidation and Reduction Oxygen: An abundant and essential oxidizing agents (oxidants)..Oxygen is the common electron acceptor in redox reactions. Example: C + O 2 = CO 2 (charcoal burning) 2H 2 + O 2 = 2H 2 O (H 2 and O 2 burning) CH 4 + 2O 2 = CO 2 + 2H 2 O(respiration) 4Fe + 3O 2 = 2Fe 2 O 3 (corrosion, rusting)

Chapter 8. (L30)-Oxidation and Reduction Oxygen: An abundant and essential oxidizing agents (oxidants)..Reaction of oxygen with other elements. Reaction with metals to form metal oxides Example: 4Fe + 3O 2 = 2Fe 2 O 3 2Mg + O 2 = 2MgO

Chapter 8. (L30)-Oxidation and Reduction Oxygen: An abundant and essential oxidizing agents (oxidants)..Reaction of oxygen with other elements. Reaction with non-metals to form non- metal oxides Example: S + O 2 = SO 2 C + O 2 = CO 2

Chapter 8. (L30)-Oxidation and Reduction Oxygen: An abundant and essential oxidizing agents (oxidants)..Reaction of oxygen with compounds Example: 2H 2 S + 3O 2 = 2SO 2 + 2H 2 O CS 2 + 3O 2 = CO 2 + 2SO 2..Ozone formation 3O 2 + hv = 2O 3

Chapter 8. (L30)-Oxidation and Reduction Other common oxidizing agents (oxidants)..Hydrogen peroxide: H 2 O 2, 30% (dangerous), 3% solution is used for mouth cleaning..Potassium dichromate: K 2 Cr 2 O 7, a very strong oxidant in acidic conditions, Cr(VI), toxic, carcinogenic (the movie); old breathalyzer test for intoxication (reacts with alcohol) by its color change (orange to green); used to be the glassware cleaning solution..Potassium permanganate: KMnO 4, a very strong oxidant in acidic conditions, Mn(VII), purple; disinfectant..Chlorine: Cl 2, quite strong oxidant; disinfectant, tap water smell, swimming pool (calcium hypochlorite, Ca(OCl) 2, pH maintained at , if too high, using HCl to lower the pH)

Chapter 8. (L30)-Oxidation and Reduction Other common oxidizing agents (oxidants)..Bleaches are oxidizing agents or oxidants. laundry bleaches are usually sodium hypochlorite, NaClO as solution (Purex, Clorox), or Ca(OCl) 2 as powder non-chlorine beaches: sodium percarbonate (a mixture of Na 2 CO 3 and H 2 O 2 ) or sodium perborate (a mixture of NaBO 2 and H 2 O 2 )

Chapter 8. (L30)-Oxidation and Reduction Quiz Time Which is oxidant and reductant, respectively, for the following reaction: 2CO + O 2 = 2CO 2 ? (a) O 2 is the reductant and CO is the reductant; (b) O 2 is the oxidant and CO is the oxidant; (c) O 2 is the reductant and CO is the oxidant; (d) O 2 is the oxidant and CO is the reductant.

Chapter 8. (L30)-Oxidation and Reduction Quiz Time Which is the oxidant in the following reaction: 2H 2 S + 3O 2 = 2SO 2 + 2H 2 O? (a) H 2 O; (b) H 2 S; (c) O 2 ; (d) SO 2.

Chapter 8. (L30)-Oxidation and Reduction Quiz Time Which is the reductant in the following reaction: 2H 2 S + 3O 2 = 2SO 2 + 2H 2 O? (a) H 2 O; (b) H 2 S; (c) O 2 ; (d) SO 2.

Chapter 8. (L30)-Oxidation and Reduction Quiz Time Which is the reductant in the following reaction: Se + O 2 = SeO 2 ? (a) H 2 O; (b) Se; (c) O 2 ; (d) SeO 2.

Chapter 8. (L30)-Oxidation and Reduction Quiz Time Which is the oxidant in the following reaction: Se + O 2 = SeO 2 ? (a) H 2 O; (b) Se; (c) O 2 ; (d) SeO 2.

Chapter 8. (L30)-Oxidation and Reduction Quiz Time Which of the following is the oxidant? (a) H 2 O; (b) Fe; (c) KMnO 4 ; (d) H 2.

Chapter 8. (L30)-Oxidation and Reduction Quiz Time Which of the following is the oxidant? (a) H 2 O; (b) Fe; (c) K 2 Cr 2 O 7 ; (d) H 2.

Chapter 8. (L30)-Oxidation and Reduction Quiz Time Which of the following is the oxidant? (a) H 2 O; (b) Zn; (c) H 2 O 2 ; (d) H 2.

Chapter 8. (L30)-Oxidation and Reduction Quiz Time Which of the following is the oxidant? (a) H 2 O; (b) CH 4 ; (c) NaClO; (d) H 2.

Chapter 8. (L30)-Oxidation and Reduction Quiz Time Which of the following is the oxidant? (a) H 2 O; (b) CH 4 ; (c) Ca(ClO) 2 ; (d) H 2.

Chapter 8. (L30)-Oxidation and Reduction Quiz Time Which is one of the major component of laundry bleaches? (a) O 2 ; (b) CH 4 ; (c) NaOCl or Ca(ClO) 2 ; (d) H 2.