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Pgs 636 - 645. Oxidation-Reduction Reactions  Reactions that occur when electrons are transferred between atoms  Also called Redox Reactions  Oxidation.

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Presentation on theme: "Pgs 636 - 645. Oxidation-Reduction Reactions  Reactions that occur when electrons are transferred between atoms  Also called Redox Reactions  Oxidation."— Presentation transcript:

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2 Oxidation-Reduction Reactions  Reactions that occur when electrons are transferred between atoms  Also called Redox Reactions  Oxidation = LOSS of electrons  Reduction = GAIN of electrons  LEO the lion goes GER

3 Oxidation – Reduction Reactions  Reaction of sodium metal with chlorine gas: 2Na (s) + Cl 2 (g)  2NaCl (s)  What’s really happening in this reaction? NaCl Each sodium gives-up an electron to the chlorine resulting in ions! Na+Cl-

4 Practice!!  In each of the following reactions, identify what is being oxidized, and what is being reduced? 2Mg (s) + O 2 (g)  2MgO (s) 2Al (s) + 3I 2 (s)  2AlI 3 (s)

5 Can reactions between nonmetals be redox reactions?  Yes, but it’s harder to see CH 4 (g) + 2O 2 (g)  CO 2 (g) + H 2 O (g) + energy  Use oxidation states to determine where the electrons are going!

6 Oxidation States  Also called oxidation numbers  Positive and negative numbers assigned to an INDIVIDUAL atom to help of keep track of electrons during redox reactions

7 Rules for Assigning Oxidation Numbers 1. Oxidation number of a free element = zero Examples  HONClBrIF, solid metals (Na, Ag) 2. Oxidation number of a monatomic ion is the same as it’s charge Examples  NaClCaCl 2 3. Oxygen’s oxidation number in compounds is -2, EXCEPT for peroxides where it is -1 Examples  O2 H2OH2O2

8 Rules for Assigning Oxidation Numbers 4. Hydrogen’s oxidation number = +1 in covalent compounds Examples  H2OHI NH3 5. For a neutral compound, the sum of the oxidation states must be ZERO Examples  CuCl2Fe2O3 6. For polyatomic ions, the sum of the oxidation numbers must equal the charge of the ion Examples  SO4 2-

9 Practice!!  Assign oxidation numbers to each of the following atoms: SO3N2O5C2H6 SO3 2- PF3

10 What do we use oxidation numbers for?  To determine what is being oxidized and what is being reduced in a redox reaction  Example:  Identify what is oxidized and reduced in the following reaction: HINT  Oxidation = INCREASE in oxidation # Reduction = DECREASE in oxidation # CH 4 (g) + 2O 2 (g)  CO 2 (g) + H 2 O (g)

11 Practice!!  Determine what is oxidized and reduced in the following reactions: Cu (s) + 2AgNO3 (aq)  Cu(NO3)2 + 2Ag Br2 (g) + 2NaF (aq)  2NaBr (aq) + F2 (g) CH3OH (g) + O2 (g)  CO2 (g) + H2O (g)

12 Two more terms to know…  Reducing Agent  electron donor  What is oxidized in the reaction  Oxidizing Agent  electron acceptor  What is reduced in the reaction  Identify the reducing agent and oxidizing agent in the previous 3 reactions: Cu (s) + 2AgNO3 (aq)  Cu(NO3)2 + 2Ag Br2 (g) + 2NaF (aq)  2NaBr (aq) + F2 (g) CH3OH (g) + O2 (g)  CO2 (g) + H2O (g)


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