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Oxidation, Reduction and Electrochemistry

Oxidation, Reduction and Electrochemistry. In this chapter you will be exposed to some basic concepts involved in a special type of chemical reaction. Time will not permit an in-depth study of this, but the main concepts will be important to learn. Oxidation-Reduction Reactions.

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Oxidation, Reduction and Electrochemistry

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  1. Oxidation, Reduction and Electrochemistry • In this chapter you will be exposed to some basic concepts involved in a special type of chemical reaction. • Time will not permit an in-depth study of this, but the main concepts will be important to learn.

  2. Oxidation-Reduction Reactions • Oxidation-Reduction reactions are also termed Redox reactions. • A redox reaction is a chemical reaction which involves the loss and gain of electrons.

  3. Redox Reactions • In a redox reaction one substance is oxidized (loses electrons) and another substance is reduced (gains electrons) • OIL RIG ( oxidation is loss, reduction is gain of electrons) • LEO the lion goes GER (loss of electrons is oxidation, gain of electrons is reduction. 2 Na(s) + Cl2(g) 2 NaCl Na – loses 1 electron (oxidized) Cl – gains 1 electron (reduced)

  4. Practice Problem • Identify the substance oxidized and reduced in the following redox equation. • Ag (s) + NO3 (aq) AgNO3

  5. Oxidation Numbers • To analyze an equation as a redox reaction it’s essential to identify the oxidation numbers of the reactants and products. • Changes in oxidation numbers reveal if a substance is oxidized or reduced.

  6. Oxidation Number Rules • When assigning oxidation numbers use the following rules: • The oxidation number for any “free” or uncombined element in atomic or molecular form is 0. • The oxidation number of a monatomic ion is equal to the charge on the ion. • The oxidation number of an atom of fluorine in a compound is always –1 because it is the most electronegative.

  7. Oxidation Numbers 4) An atom of the more electronegative element in a binary compound is assigned the number equal to its ion charge. • In compounds, atoms of group I, II, and aluminum have positive oxidation numbers : +1, +2, +3 respectively. • Hydrogen is +1 unless combined with a metal atom, then its –1. • The oxidation number of oxygen is usually –2. When combined with fluorine it is +2. In peroxides, such as H2O2 oxygen has the oxidation number –1.

  8. Oxidation Numbers 8) The sum of the oxidation numbers of all atoms in a particle must equal to zero in a compound and to its charge for a polyatomic ion.

  9. Oxidation Number Practice • NH4+ : • Al : • BF3 : • KClO3 • CO32-

  10. Oxidation Number Practice • NH4+ : H= +1 N= -3 • Al : 0 • BF3 : F=-1 B: +3 • KClO3 K=+1 O= -2 Cl= +5 • CO32- O= -2 C=+4

  11. Identifying Redox Reactions • To identify a redox reaction you must analyze the oxidation numbers of reactants and products. Redox Reaction

  12. Identify oxidized and reduced substance: 1) Cl2 + 2HBr  2HCl + Br2 +1 -1 0 +1 -1 0 Assign oxidation numbers to each atom in the equation. Consider only the atoms for which there was a change in oxidation number.

  13. Identify oxidized and reduced substance: 1) Cl2 + 2HBr  2HCl + Br2 +1 -1 0 +1 -1 0 An increase in oxidation number indicates an oxidation. A decrease in oxidation number indicates a reduction. The oxidation number of Cl decreased (from 0 to -1): Cl was reduced The oxidation number of Br increased (from -1 to 0): Br was oxidized

  14. Identify oxidized and reduced substance: 2) 2H2 + O2 2H2O 0 0 +1 -2 An increase in oxidation number indicates an oxidation. A decrease in oxidation number indicates a reduction. The oxidation number of O decreased (from 0 to -2): O was reduced The oxidation number of H increased (from 0 to +1): H was oxidized

  15. Classwork • Oxidizing and reducing handout

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