U4 S1 L3 Balancing by redox Textbook Readings MHR page 730: The Half-Reaction Method for Balancing Equations page 731: Balancing Half-Reactions page 732: Balancing Half-Reactions for Acidic Solutions page 733: Balancing Half-Reactions for Basic Solutions pages 734-736: Half-Reaction Method for Balancing Redox Reactions pages 736-738: Balancing Redox Reactions for Acidic and Basic Solutions pages 742-744: Stoichiometry and Redox Titrations Textbook Practice Items MHR page 732: items 17, 18, 19 and 20 page 734: items 21, 22, 23 and 24 pages 738-739: items 27 and 28 page 744: items 29, 30, 31 and 32 pages 745-746: items 1-9

Upon completion of this lesson, you should be able to: write and balance equations for complex oxidation-reduction reactions occurring in acidic or basic solutions   solve redox stoichiometry problems for spontaneous redox reactions

The first thing we have to do when balancing redox equations is to make sure the reaction is indeed a redox reaction. Therefore, we must check to make sure that a species is being reduced and one is being oxidized. Once the redox species have been identified we can proceed to balance the equation. Balancing by half reactions: (balancing by electrons!) Potassium reacts with Chlorine to produce potassium chloride.

~~The No Fail 6 Step Method~~ p 732 Balancing Redox Reactions in Acidic Conditions: ~~The No Fail 6 Step Method~~ p 732 Write the half reaction for the species being oxidized and reduced. Balance: Atoms other than O and H Balance O using H2O Balance H using H+ (hence acidic conditions!) Balance each half reaction electrically using electrons (e-). Net charge must be zero. Balance each half reaction so that the number of electrons in each is the same. Simplify. Combine both equations (cross out/add/subtract - just like in math). Check the numbers, kinds of atoms and net charge.

Write a balanced half reaction for that shows the reduction of permanganate ions to manganese (II) under acidic conditions.

Balance the following chemical equation under acidic conditions

~~The No Fail 7 Step Method~~ p 733 Balancing Redox Reactions in Basic Conditions: ~~The No Fail 7 Step Method~~ p 733 Write the half reaction for the species being oxidized and reduced. Balance: Atoms other than O and H Balance O using H2O Balance H using H+ (hence acidic conditions!) Balance each half reaction electrically using electrons (e-). Net charge must be zero. Change from acidic to basic – look at the H+, add the same number of OH - to both sides. On the side H+ is on form water (H+ + OH - H2O). Balance each half reaction so that the number of electrons in each is the same. Simplify. Combine both equations (cross out/add/subtract - just like in math). Check the numbers, kinds of atoms and net charge.

Write a balanced half reaction for the oxidation of thiosulphate ions to sulfite ions in basic conditions

Balance the following under basic conditions:

Balancing redox by Ox # method – p 747 : The short cut! Write equation Assign Ox #’s Identify atoms involved in redox Find numerical value of change Determine ratio of atoms Balance Balance O with H2O and H with H+

Balance under acidic conditions

Using the Standard reduction potential Table. Write the redox reaction equation for the reaction between zinc metal and aqueous chromium(III) sulphate List the reactant species present