Oxidation & Reduction Reactions in which some elements change their oxidation number.

Oxidation Numbers An oxidation number is the charge an atom would have if electrons in its bonds belonged completely to the more electronegative atom. ClO 2 Cl can have several oxidation numbers: -1,+1,+3,+5,+7

Redox Reaction A chemical reaction in species change their oxidation number: Na + Cl 2 => NaCl

What’s the point ? Electrical production (batteries, fuel cells) REDOX reactions are important in …

Rules

Determine the oxidation number of each atom in each of the following formulas: (a)O 2 (b) CH 4 (c) NaCl (d) SO 4 -2 (e) KMnO 4

Practice Assigning Oxidation Numbers NO 2 N2O5N2O5 HClO 3 HNO 3 Ca(NO 3 ) 2 KMnO 4

Practice Assigning Oxidation Numbers Fe(OH) 3 K 2 Cr 2 O 7 CO 3 2- CN - K 3 Fe(CN) 6

Practice Assigning Oxidation Numbers NO 2 N= +4, O = -2 N2O5N2O5 N = +5, O = -2 HClO 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 KMnO 4 K=+1, Mn=+7, O= -2

Practice Assigning Oxidation Numbers Fe(OH) 3 Fe =+3, O=-2, H=+1 K 2 Cr 2 O 7 K=+1, Cr=+6, O=-2 CO 3 2- C=+4, O =-2 CN - C=+4, N=-5 K 3 Fe(CN) 6 K=+1, Fe=+3, C=+4, N=-5

Lab: Corrosion of Iron An important aspect of the use of some metals, particularly of iron, is the possibility of corrosion. Rust is apparently a hydrated form of iron(III)oxide Fe 2+ (aq) + O 2 (g) + H 2 O(l) → Fe 2 O 3 H 2 O(s) rust

Galvanic Corrosion Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially to another when both metals are in electrical contact. Zinc

What do we do with oxidation numbers? The oxidation numbers of atoms in an equation allow us to determine which element is oxidized and which is reduced in a redox reaction. 6Cd + 2 FeBr 3 => 3 Cd 2 Br Fe

LEO

LEO says GER!

LEO says Loss of Electrons = Oxidation Gain of Electrons = R eduction GER!

Oxidation and Reduction Apply oxidation numbers to all particles and identify the oxidized and the reduced elements. Mg + HCl => MgCl 2 + H 2 F 2 + AlBr 3 => AlF 3 + Br 2

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 Zn + CuSO 4  ZnSO 4 + Cu

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 Zn + CuSO 4  ZnSO 4 + Cu

Exercise For each of the following reactions find the element oxidized and the element reduced Cl 2 + KBr  KCl + Br 2 Cu + HNO 3  Cu(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

Exercise For each of the following reactions find the element oxidized and the element reduced Cu + HNO 3  Cu(NO 3 ) 2 + NO 2 + H 2 O

Oxidation-Reduction Reactions (Redox) All oxidation reduction reactions have element reduced and one one element oxidized.

Why is the Statue of Liberty green?

Replica – Ellis Island

Acid Rain causes the copper to turn into copper oxide, copper sulfate, copper hydroxide or copper chloride because of the oxidation-reduction reaction and this is basically copper salts or in other words, tarnish. Things like statues, pennies, or pipes made of Copper turn green over a period of time. This happens due to oxidation.

Corrosion of steel, whether in atmospheric, soil, water, or chemical exposure, annually costs the economy about 3.1% of the Gross Domestic Product (GDP). Estimates show 25-30% of corrosion could be eliminated if proper corrosion protection methods, such as: galvanizing, painting, stainless or weathering steel were employed.

Steel Steel is an alloy made by combining iron and another element, usually carbon. When carbon is used, its content in the steel is between 0.2% and 2.1% by weight, depending on the grade. Other alloying elements sometimes used are manganese, chromium, vanadium and tungsten.alloyironcarbongrademanganese chromiumvanadiumtungsten

Corrosion of Iron When iron rusts a spontaneous redox reaction occurs, between the oxygen and iron. If water is added the rusting occurs more rapidly.

Oxidation : Fe(s) → Fe 2+ (aq) + 2e- Equation 1 Reduction : O 2 (g) + 2H 2 O(l) + 4e- → 4OH-(aq) Equation 2

4Fe(OH) 2 (s) + O 2 (g) + xH 2 O(I)→ 2Fe 2 O 3 (x)H 2 O(s) Equation 5 RUST 3Fe 2+ (aq) + 2Fe(CN) 6 3- (aq) → Fe 3 [Fe(CN) 6 ] 2 (s) Equation 6 Yellow Prussian blue

Corrosion of Iron Corrosion of iron is called rusting. Rust is Fe 2 O 3 x.H 2 O. Many metals like iron, steel, polymers, ceramic etc are damaged due to some natural process. Corrosion is one of them.