Oxidation Numbers, ox #

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Helen Short
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1 Oxidation Numbers, ox # are or numbers assigned to each or assuming that the are transferred from the electronegative element to the electronegative element. now mimic systems. ox # are written followed by and are assigned using the following: Oxidation Number Rules The ox # of an in it s pure form, (eg. Pb(s), O2(g) ) is. The ox # of a is equal to the on that. eg. Cl 1- The algebraic of the oxidation numbers in a polyatomic compound is. eg. Mg3N2 Fe(NO3)3 The most common ox # for O is, in peroxides it is, and in compounds with fluorine it is.

2 The most common ox # of H is, in metal hydrides it is. The algebraic of the oxidation numbers in a polyatomic is equal to the on the. eg. Cr2O7 2- Assign the ox# to the most element Determine the charge for that element Considering the charge on the ion or neutral compound, find the total charge for the other element, then its ox #. In compounds of, the ox # of the electronegative atom is and the ox # of the electronegative atom is. eg. CO2 In a covalent bond, the more atom takes the in the bond.

3 Energy Transfer Theory Chemical reactions with the of. Often, this energy is noticeable as it doesn t involve a change or the production of or. This is true of reactions, where the switch between entities with no change in. To examine the energy we the chemical reaction into separate reactions called. For: Net ionic equation Half reactions

4 The energy is the electron Redox reactions require the reaction to occur simultaneously with the reaction Redox goes Balancing REDOX Reactions 1. Assign (ox. #) to element in the rxn and the species being and. 2. Write separate (1/2 rxn), for the (ox.) and (red.) processes.

5 3. Balance the that undergo or. 4. Add the total gained or lost in ox. or red. rxn. 5. Multiply each so that once combined, the total # of e-s out. 6. Combine the. 7. Balance the net (due to ions) using ions to one side (for acidic sol n) or with ions (for basic sol n). 8. Add to balance and. 9. Check that the final eq n is.

8 Predicting Redox Reactions Redox Rxn occur due to the of e - from substance to. is a of e - between. if substance e - from another, a rxn. eg. Cu + 2Ag + Cu Ag Reducing agents (RA) a substance that e - to another substance and undergoes. Oxidizing agents (OA) a substance that e - to another substance and undergoes. eg. Cu + 2Ag + Cu Ag

9 rxns are listed as, S = Strong, W = Weak. SOA OA1 + ne - RA1 WRA WOA OA2 + ne - RA2 SRA spontaneous rxns occur only if the is and to the of the. For spontaneous rxn: eg. Will a mixture of aqueous chromium (II) nitrate and tin (II) nitrate react and if so what is the overall equation? List all species determine the, on the and the, on the on the REDOX table

10 eg. Create ½ rxns from the following reaction data and place in order of strongest to weakest OA: Ion/metal Zn Pb Ag I 1- Zn 2+ Pb 2+ Ag + I 2

11 eg. Create ½ rxns from the following reaction data and place in order of strongest to weakest OA: Cu2+ + Pb Cu + Pb2+ Ag + Br2 AgBr Ag+ + Cu Ag + Cu2+ Au + Br2 no rxn

12 eg. Create ½ rxns from the following reaction data and place in order of strongest to weakest OA: W + M2 W2+ + M1- Y2+ + Z Y + Z2+ X + M2 no rxn W + Y2+ no rxn X2+ + Z X + Z2+

13 Standard Reduction Potentials ( also p 805) E (volts) F2 + 2 e - 2 F S2O e - 2 SO Co 3+ + e - Co Pb e - Co H2O2 + 2 H e - 2 H2O Au + + e - Au PbO2 + SO H e - PbSO4 + 2 H2O MnO H e - Mn H2O Au e - Au Ce 4+ + e - Ce ClO H e - Cl H2O Cl2 + 2 e - 2 Cl HNO H e - N2O + 3 H2O Cr2O H e - 2 Cr H2O O2 + 4 H e - 2 H2O MnO2 + 4 H e - Mn H2O IO H e - I2 + 6 H2O Br2 + 2 e - 2 Br AuCl e - Au + 4 Cl Hg e - Hg ClO 1- + H2O + 2 e - Cl OH Ag + + e - Ag NO H + + e - NO2 + H2O Hg e - 2 Hg Fe 3+ + e - Fe O2 + 2 H e - H2O MnO H2O + 3 e - MnO2 + 4 OH I2 + 2 e - 2 I Cu + + e - Cu O2 + 2 H2O + 4 e - 4 OH Cu e - Cu SO H e - SO2 + 2 H2O SO H e - H2SO3 + H2O Sn e - Sn

14 Cu 2+ + e - Cu S + 2 H e - H2S AgBr + e - Ag + Br H e - H Fe e - Fe Pb e - Pb Sn e - Sn AgI + e - Ag + I Ni e - Ni Co e - Co H3PO4 + 2 H e - H3PO3 + H2O Tl + + e - Tl PbSO4 + 2 e - Pb + SO Se + 2 H e - H2Se Cd e - Cd Cr 3+ + e - Cr Fe e - Fe S + 2 e - S Ga e - Ga Ag2S + 2 e - 2 Ag + S Cr e - Cr Zn e - Zn Te + 2 H e - H2Te H2O + 2 e - 2 OH 1- + H Cr e - Cr Se + 2 e - Se SO H2O + 2 e - SO OH Te + 2 e - Te Mn e - Mn V e - V Al e - Al Ti e - Ti Mg e - Mg Ce e - Ce Na + + e - Na Ca e - Ca Ba e - Ba Cs e - Cs Ra e - Ra K + + e - K Li + + e - Li -3.00

15 Electrochemical Cells (Galvanic, Voltaic, Electric) the reactions are occurring and are by a the e - occurs through this circuit the difference is manifested as. As the cell proceeds: mass of electrode Solution electrical charge Ions from salt bridge Cathode Anode

16 Cell Shorthand Notation eg. For the Zn/Cu cell: Conventions: the notation indicates a phase where the and are in physical contact. the notation represents the or if additional are or specific are, they are written with the separated by a or a. if the cell has no for the electrode, electrodes or are used: standard cells are at all sets of information REDOX equation, cell diagram and the cell notation are related and if is provided, the other should be able to be.

17 Calculating Cell Potential, E cell for each the is listed on the chart on p. 805 or the reference sheet. the complete is a combination of the and half reactions - the of the two is the potential, this is the usable energy given by: as all half reactions are listed as rxns, the oxidation reaction the sign, so: eg. Calculate the E cell for the following unbalanced equation: Br 2 + Cu 2 Br + Cu +

18 eg. a) Determine the anode, cathode and calculate the standard cell potential produced by a galvanic cell consisting of a Sn electrode in contact with a solution of Sn2+ ions and a Cr electrode in contact with a solution of Cr3+ ions. b) Write the shorthand cell notation. eg. Use complete half-reactions and potentials to predict whether the following reaction is spontaneous or nonspontaneous in aqueous solutions. If the cell is spontaneous, write the cell shorthand notation. O SO OH 1-2 SO H 2 O YOU MUST READ 9.6 Corrosion p before the next lesson

19 Reactions of Metals with Water The is the and will be. The and in it will be the. Need to consider: i) - of the 3 ii) this requires a very long, or an, as O2 is not very water iii) - as with Metals the will be That s why: Not metals with eg. ones that : ones that : Not metals with eg. ones that : ones that : Not metals with eg. ones that : ones that :

20 Metals with Metals Alloys are to change a metal s. As undergo rust, corrosion, patina metals are to stop the. eg. or need protection. The metal, called a, is on the table to the in. It will the and the. eg. Which metals will Fe? eg. Which metals will Fe? eg. a) Will Cr protect Fe? Determine the anode and calculate the cell potential if the cathode is oxygenated water. b) Do the same for Ag and Fe.

21 Cells and Spontaneity Reactants Products ΔEcell Cell Type Spontaneity Electrolytic cells, ΔE < 0 requires source of to the within the cell. e - are from the and to the by the. rxn is then the of the rxn. used to and to produce. Solution rxns so could be the and/or the reaction.

22 eg. KI solution and battery Cathode (red): Er º (V) Anode (ox): Eo º (V) e - from the (-ve) of the reduce the e - from the flow to the (+ve) of the to complete the. forms and from an sol n!

23 versus

24 eg. Given the following molten system, AgCl, predict the products at each electrode. Assume inert electrodes and sufficient voltage to cause a reaction to take place. Consider all possible rxns. eg. Given a 1.00 M solution of SnI 2 at 25 C, predict the anode and cathode half cell reactions. What is the minimum voltage required for each cell to operate?

25 Stoichiometry of Cell Reactions Basic Concepts 1. q = It where: 1C = q = I = t = 2. Faraday s Law: the of a substance or is related to the transferred 3. Faraday = F = 4. eg.1 Calculate the amount of charge which passes through an electrolytic cell with a current of 1.80A for 5.0 min.

26 eg. 2 Calculate the mass of Zn deposited by a current of 2.50 A operating over 30.0 min in an electrolytic cell containing Zn(NO 3 ) 2(aq). eg. 2 Two cells are connected in series, attached using inert electrodes. The first cell contains Sn2+ and second contains Ga3+. If 3.75 g of Sn is obtained in the first cell, calculate the mass of Ga that will be produced in the second cell.

Oxidation & Reduction (Redox) Notes

Oxidation & Reduction (Redox) Notes Chemical Activity (or Chemical Reactivity) is the measure of the reactivity of elements. If an element has high activity, then it means that the element is willing to