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Redox Reactions

Redox Reactions. What is redox?. Redox reactions involve a transfer of electrons. Oxidation – involves losing electrons (increase in oxidation number) Reduction – involves gaining electrons (reduction in oxidation number) LEO the lion says GER Losing electrons = oxidation

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Redox Reactions

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  1. Redox Reactions

  2. What is redox? • Redox reactions involve a transfer of electrons. • Oxidation – involves losing electrons (increase in oxidation number) • Reduction – involves gaining electrons (reduction in oxidation number) • LEO the lion says GER • Losing electrons = oxidation • Gaining electrons = reduction

  3. How do you know if a reaction is redox or not? • Oxidation numbers can be assigned to all atoms based on electronegativity relative to the other atoms to which they are bonded. • If oxidation numbers change from one side of the equation to the other, that indicates that the reaction is a redox reaction.

  4. Rules for Assigning Oxidation Numbers • The oxidation number of an atom in the elemental state is zero.Example: Cl2 and Al both are 0 • The oxidation number of a monatomic ion is equal to its charge.Example: In the compound NaCl, the sodium has an oxidation number of 1+ and the chlorine is 1-. • The algebraic sum of the oxidation numbers in the formula of a compound is zero.Example: the oxidation numbers in the NaCl above add up to 0 • The oxidation number of hydrogen in a compound is 1+, except when hydrogen forms compounds called hydrides with active metals, and then it is 1-.Examples: H is 1+ in H2O, but 1- in NaH (sodium hydride). • The oxidation number of oxygen in a compound is 2-, except in peroxides when it is 1-, and when combined with fluorine. Then it is 2+.Example: In H2O the oxygen is 2-, in H2O2 it is 1-. • The algebraic sum of the oxidation numbers in the formula for a polyatomic ion is equal to the charge on that ion.Example: in the sulfate ion, SO42-, the oxidation numbers of the sulfur and the oxygens add up to 2-. The oxygens are 2- each, and the sulfur is 6+.

  5. Examples • NaCl • HNO3 • CaCO3 • PO4-3

  6. Redox Reactions • Identify which of the following equations represent redox reactions. • For each redox equation identified, write the oxidation state above each element. • Indicate the element that has been oxidized and the one that has been reduced.

  7. examples • KClO3 KCl + O2 • NaOH+ HClNaCl + H2O k • CO2 + H2O  C8H12O2+ O2 • NaCl + AgNO3  NaNO3 + AgCl

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