Entry Task: Sept 18-19 th Block 1

1. Entry Task: Sept 18-19th Block 1 Question: What are the oxidation numbers of each of the following? KMnO4 You have 5 minutes

2. Oxidation-Reduction Reactions

3. Oxidation-Reduction (Redox) Reactions in which electrons are transferred between substances

4. Use of Oxidation numbers in determining redox reactions is basically a bookkeeping method for keeping track of electrons You must be able to identify an oxidation-reduction reaction. But first, we must learn the rules for assigning oxidation #’s to different species.

5. Rules for oxidation numbers • Atoms in elemental form are 0. • Monatomic ion; charge of the ion is its oxidation number. • Nonmetals; usually negative numbers. a.) oxygen = -2 unless a peroxide = -1 b.) Hydrogen +1 with nonmetals, -1 with metals c.) Halogens (-1) unless bonded to oxygen (+) in a polyatomic ion (Ex: ClO3-; Cl = +5) 4) Sum of oxidation numbers must = 0 5) Most electronegative (furthest to right and up) element gets a negative charge. See pages 128 – 129 for more on this.

6. Atoms in elemental form are 0. • Examples • Ag • Pb • Cl2 • O2 • Oxidation # = 0 for 7 diatomic elements and for all other elements when by themselves.

7. Monatomic ion-- • charge of the ion is its oxidation number. • Examples • AgCl Ag = +1 Cl = -1 • PbI2 Pb = +2 I = -1 • Fe2O3 Fe = +3 O = -2

8. 3) Nonmetals; usually negative numbers. a.) oxygen = -2 unless a peroxide = -1 b.) Hydrogen +1 with nonmetals, -1 with metals c.) Halogens (-1) unless bonded to oxygen (+) in a polyatomic ion (Ex: ClO3-; Cl = +5) Examples PbO oxygen = -2 Na2O2 oxygen = -1 H2S hydrogen = +1 NaH hydrogen = -1 KI iodine = -1 KIO2 iodine = + 3

9. Determine Oxidation # of element red element in each of the following: CaH2 -1 SO42- +6 Na2S -2 Mg(NO3)2 +5 Br2 0 HClO4 +7 H2SO4 +6 PO33- +3 MnO2 +4 KMnO4 +7 BrO2- +3 BrO3- +5

10. Again, oxidation reduction reactions occur when there is a transfer of electrons from one species to another in a reaction. • If one reactant gains electrons another must lose electrons. • Reduction is always accompanied by oxidation.

11. Oxidation-Reduction Reactions • An atom that becomes more positively charged is oxidized. • This is due to loss of e-. • The gain of electrons by an atom is called reduction.

12. Two mnemonics for remembering which substance is undergoing oxidation and which is undergoing reduction? - OIL -- RIG Oxidation Involves Loss -- Reduction Involves Gain “Leo the lion says Ger” Loss of electrons oxidation -- Gain of electrons reduction

13. Many metals react with O2 in • the air to form metal oxides. • Metals lose electrons to oxygen. • 2 Fe + O2 2 FeO • As Fe is oxidized (loses e-), • oxygen is reduced (gains e-). • Reduction is gain

14. 2 Fe + O2 2 FeO 0 0 +2 -2 oxidation reduction

15. Oxidation of metals by acids and salts • Reaction of a metal with either an acid or metal salt follows general form of: A + BX AX +B • Single displacement reaction

16. +2+6-2 0 +2+6-2 0 CuSO4(aq) + Zn(s)  ZnSO4(aq) + Cu(s) Reduced Oxidized What are the products? What are the charges on each species? What is oxidized and what is reduced?

17. For the following reactants: • Write the reaction that occurs. • Identify what is being oxidized and reduced. Magnesium + Hydrochloric Acid Aluminum + Cobalt(II) Nitrate

18. Mg(s) + HCl (aq)  MgCl2 (aq) + H2(g) 0 +1 +2 0 reduction oxidation

19. Al(s) + Co(NO3)2 (aq)  Al(NO3)3(aq) + Co(s) +2 +3 0 0 reduction oxidation

20. Types of Redox Reactions • Combination (synthesis) • Decomposition • Displacement • hydrogen, metal, halogen • Combustion

21. Activity Series • List of metals in order of decreasing ease of oxidation. • Alkali and alkaline earth metals are at the top. (active metals) • Gold, Silver, Platinum, and palladiumare considered to be (noble metals) because they resist oxidation.

22. Using activity series to predict reactions • Activity series can be used to predict reactions between metals and metal salts or acids. • Any metal listed on the series can be oxidized by the ions of elements below it on the list.

24. Displacement Reactions – Metal Displaces H from acid or water • Metal + Acid -> Salt + H2 (g) • Metal + Water -> Base + H2(g) • Use Activity Series to Know if a Reaction Will Happen

25. Activity Series

26. Using activity series of metals, which metals from the list below can be oxidized by H+? Ni Al Cu Pb Ag Mg Au

27. Chemical Reaction Types • Decomposition • Synthesis • Single Replacement • Combustion • Precipitation • Neutralization Types of Redox Reactions Types ofDouble ReplacementReactions

28. What are the 7 Diatomic Elements H2 – hydrogen N2 – nitrogen O2 – oxygen F2 - fluorine Cl2 – chlorine Br2 – bromine I2 – Iodine

29. Synthesis A + B  AB Examples H2 (g) + O2 (g)  H2O (g) Mg (s) + O2 (g)  MgO (s) Na (s) + Cl2 (g)  NaCl (s)

30. Decomposition AB  A + B Examples NaCl (s) Na (s) + Cl2 (g) KClO3 (s) KCl (s) + O2 (g) elec

31. Single Replacement A + BC  AC + B Examples Na (s) + HOH (l) NaOH (aq) + H2 (g) sodium replaces hydrogen in water Cl2 (g) + NaBr (aq)  Br2 (l) + NaCl (aq) chlorine replaces bromine in sodium bromide

32. Double Replacement (Metathesis) AB + CD  AD + BC Examples AgNO3 (aq) + NaCl(aq)AgCl(s)+ NaNO3 (aq) HCl(aq) + NaOH(aq)  NaCl(aq) + H2O (l) NH4Cl (aq) + NaOH(aq) NH3 (g) + H2O (l) + NaCl(aq) Rust color for the products represents the driving force which allows the chemical reaction to occur.

33. Combustion hydrocarbon + oxygen  carbon dioxide + water Examples CH4 (g) + O2 (g) CO2 (g) + H2O (l) C3H8 (g)+ O2 (g) CO2 (g) + H2O (l) CH3OH(g)+ O2 (g) CO2 (g) + H2O (l) CO2 + H2O

34. Neutralization Reactions Strong Acid + Strong Base  Salt + Water Example HCl(aq) + NaOH(aq)  NaCl(aq) + H2O (l) H+ + Cl- + Na+ + OH-  Na+ + Cl- + H2O(l) H+ + OH-  H2O