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Lecture11Redox&amp;Chapter5inked

# Lecture11Redox&amp;Chapter5inked - Chapter 4 Reactions...

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Chapter 4 Reactions in Aqueous Solutions Chapter 5 Periodicity and Atomic Structure Lecture 11 (CHEM 1010) Agenda: Balancing Redox Reactions The Oxidation number method The Half-Reaction Method Waves and Light Maxwell and electromagnetism Atomic line spectra Bohr model of the atom de Broglie Equation The Uncertainty principle

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Step 1 : Balance the equation for all atoms other than H and O. Step 2 : Assign oxidation numbers to all atoms. Step 3 : Decide which atoms have changed oxidation number, and by how much. Step 4 : Make the total increase in oxidation number equal to the total decrease in oxidation number. Step 5 : Balance the equation for O by adding H2O, and then balance for H by adding H+ (stop here if the solution is acidic). Step 6 : If the reaction takes place in a basic solution a number of OH- ions equal to the H+ ions is added to both sides of the reaction. The Oxidation number method
Balance the following net ionic equation in both acidic and basic solution using the oxidation-number method: Cr3+( aq ) + IO3-( aq ) I-( aq ) + Cr2O72-( aq ) Step 1 : Balance the equation for all atoms other than H and O. 2 Cr3+( aq ) + IO3-( aq ) I-( aq ) + Cr2O72-( aq ) Balancing REDOX Reactions (Oxidation-Number Method)

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Step 2 : Assign oxidation numbers to all atoms. 2Cr3+( aq ) + IO3-( aq ) I-( aq ) + Cr2O72-( aq ) -2 -1 -2 +6 +3 +5 Balancing REDOX Reactions (Oxidation-Number Method)
Step 3 : Decide which atoms have changed oxidation number, and by how much. 2 Cr3+ I- ( aq ) + O72-( aq ) ( aq ) + I O3- +5 +3 reduction Cr2 -1 +6 oxidation Balancing REDOX Reactions (Oxidation-Number Method)

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I O3-(aq) Step 4 : Make the total increase in oxidation number equal to the total decrease in oxidation number. 2 Cr3+ I- ( aq ) + O72-( aq ) ( aq ) + +5 +3 Cr2 -1 +6 Net decrease = -6 Net increase = +6 Balancing REDOX Reactions (Oxidation-Number Method)
Step 5 : Balance the equation for O by adding H2O, and then balance for H by adding H+ (stop here if the solution is acidic). 2Cr3+( aq ) + IO3-( aq ) + 4H2O( l ) 8H+( aq ) + I-( aq ) + Cr2O72-( aq ) Balancing REDOX Reactions (Oxidation-Number Method)

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Step 6 : If the reaction takes place in a basic solution a number of OH- ions equal to the H+ ions is added to both sides of the reaction: 2Cr3+( aq ) + IO3-( aq ) + 8OH-(aq) 4H2O(l) + I-( aq ) + Cr2O72-( aq ) Balancing REDOX Reactions (Oxidation-Number Method) 2Cr3+( aq ) + IO3-( aq ) + 4H2O( l ) + 8OH-(aq) 8H2O(l) + I-( aq ) + Cr2O72-( aq ) 2Cr3+( aq ) + IO3-( aq ) + 4H2O( l ) + 8OH-(aq) 8OH-(aq) + 8H+( aq ) + I-( aq ) + Cr2O72-( aq )
(Oxidation-Number Method) Challenge MnO4-(aq) + Br-(aq) MnO2(s) + BrO3-(aq) Basic

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(Oxidation-Number Method) Challenge
Step 1: Assign Oxidation numbers. Step 2: Break reaction into two half-reactions. Step 3: Balance atoms being oxidized or reduced. Step 4: Balance electrons. Step 5: Balance oxygen atoms. Step 6 : Balance hydrogen atoms. Step 7: Multiply and add half reactions. Step 8: Balancing in basic solution. Add OH- equal to H+ to both sides of reaction. H+ + OH- forms H2O. Cancel excess H2O to get final balanced eqn.

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Lecture11Redox&amp;Chapter5inked - Chapter 4 Reactions...

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