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Chapter 20. Oxidation-Reduction Reactions. Oxidation and Reduction. Oxidation and reduction always occur simultaneously Oxidation the complete or partial loss of electrons or gain of oxygen Reduction the complete or partial gain of electrons or loss of oxygen
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Chapter 20 Oxidation-Reduction Reactions
Oxidation and Reduction • Oxidation and reduction always occur simultaneously • Oxidation the complete or partial loss of electrons or gain of oxygen • Reduction the complete or partial gain of electrons or loss of oxygen LEO the lion goes GER OIL RIG
Oxidation and Reduction • Oxidation-reduction reaction a reaction that involves the transfer of electrons between reactants • Also referred to as a redox reaction Mg + S Mg+2 + S-2 **For now, we do not know how to predict whether it is a redox reaction or not…that’s coming soon! ☺
Oxidation and Reduction • The substance losing electrons is said to be oxidized • The substance gaining electrons is said to be reduced Mg Mg+2 + 2e- Mg is being oxidized S + 2e- S-2 S is being reduced
Oxidation and Reduction • Where did the electrons lost by magnesium go? • They were gained by sulfur Mg + S Mg+2 + S-2
Oxidation and Reduction • Reducing agent the substance being oxidized • Oxidizing agent the substance being reduced ►Magnesium reduces sulfur by losing it’s electrons ►Sulfur oxidizes magnesium by gaining magnesium’s electrons
Oxidation and Reduction • Determine what is oxidized and what is reduced in the following reaction. Identify the oxidizing agent and the reducing agent. 2Na + S 2Na+1+ S-2
Oxidation and Reduction • Oxidation is losing electrons, reduction is gaining electrons • When a substance loses electrons, it’s charge becomes more positive • When a substance gains electrons, it’s charge becomes more negative Oxidation: 2Na 2Na+1 Reduction: S S-2 • Na is the reducing agent, S is the oxidizing agent + 2e- + 2e-
Try it on your own! • Determine what is oxidized and what is reduced in the following reaction. Identify the oxidizing agent and the reducing agent. 4Al + 3O2 4Al+3 + 6O-2
Oxidation and Reduction • We have been looking at ionic compounds, so the transfer of electrons makes sense. But, what if we are dealing with a covalent compound? • How can oxidation and reduction occur if the substances can not transfer electrons? • Look back at the definition of oxidation and reduction.
Oxidation and Reduction • Oxidation the complete or partial loss of electrons or gain of oxygen • Reduction the complete or partial gain of electrons or loss of oxygen 2H2 + O2 2H2O H – H O – O H – O Equal sharing of electrons Oxygen is more electronegative, therefore the electrons are shifted away from hydrogen toward oxygen Equal sharing of electrons H
Oxidation and Reduction • Isn’t there an easier way to do this for covalent compounds, Mrs. Harnew?!? Yes! There is…but you have to memorize a few rules
Oxidation Numbers • Oxidation number a positive or negative number assigned to an atom to indicate its degree of oxidation or reduction • It shows the electron distribution • From the reactant to the product, if the oxidation number… • Increases = oxidation • Decreases = reduction
Assigning Oxidation Numbers • Determine the oxidation numbers of each element in UF6 UF6 Oxidation state: +6 -1 Sum: +6 -6 = 0
Assigning Oxidation Numbers • Determine the oxidation numbers of each element in SO4-2 SO4-2 Oxidation state: +6 -2 Sum: +6 -8 = - 2
Assigning Oxidation Numbers • Determine the oxidation numbers of each element in KClO3 KClO3 ClO3-1 Oxidation state: +1 +5 -2 Sum: +1 +5 -6 = 0 +5 -2 Oxidation state: Sum: +5 -6 = -1
Oxidation Numbers • Use the changes in oxidation numbers to identify which atoms are oxidized and which are reduced in the following reaction. 2KNO3 2KNO2 + O2