SCH100 Balancing Redox reactions.html

SCH100 Balancing Redox reactions.html - Skip to main...

This preview shows page 1 - 3 out of 14 pages.

Skip to main content You are logged in as Kwendo Alex ( Log out ) Page path Home / ► Courses / ► PURE AND APPLIED SCIENCES / ► Chemistry / ► SCH100 / ► Topic 7 / ► Balancing Redox reactions Balancing Redox Equations It is not always possible to balance redox equations using the simple “inspection” technique. The following unbalanced net ionic equation provides an example. Au 3+ (aq) + I (aq) Au(s) + I 2 (s) At first glance, it seems that this equation can be balanced by placing a 2 in front of the I . Au 3+ (aq) + 2I (aq) Au(s) + I 2 (s) Note, however, that although the atoms are now balanced, the charge is not. The sum of the charges on the left is +1, and the sum of the charges on the right is zero, as if the products could somehow have one more electron than the reactants. To correctly balance this equation, it helps to look more closely at the oxidation and reduction that occur in the reaction. The iodine atoms are changing their oxidation number from 1 to 0, so each iodide ion must be losing one electron. The Au 3+ is changing to Au, so each gold(III) cation must be gaining three electrons. The half-reactions are: I (aq) ½I 2 (s) + e Au 3+ (aq) + 3e Au(s) We know that in redox reactions, the number of electrons lost by the reducing agent must be equal to the number of electrons gained by the oxidizing agent; thus, for each Au 3+ that gains three electrons, there must be three I ions that each lose one electron. If we place a 3 in front of the I and balance the iodine atoms with a 3/2 in front of the I 2 , both the atoms and the charge will be balanced. Au 3+ (aq) + 3I (aq) Au(s) + 3/2I 2 (s)
Image of page 1

Subscribe to view the full document.

or 2Au 3+ (aq) + 6I (aq) 2Au(s) + 3I 2 (s) Balancing Redox Equations Using the Oxidation Number Method In most situations that call for balancing an equation, you are not told whether the reaction is redox or not. In these circumstances, you can use a procedure called the oxidation number method, which is outlined below. Sample Study Sheet: Balancing Redox Equations Using the Oxidation Number Technique Tip-off – If you are asked to balance an equation and if you are not told whether the reaction is a redox reaction or not, you can use the following procedure. General Steps Step 1: Try to balance the atoms in the equation by inspection, that is, by the standard technique for balancing non-redox equations. (Many equations for redox reactions can be easily balanced by inspection.) If you successfully balance the atoms, go to Step 2. If you are unable to balance the atoms, go to Step 3. Step 2: Check to be sure that the net charge is the same on both sides of the equation. If it is, you can assume that the equation is correctly balanced. If the charge is not balanced, go to Step 3.
Image of page 2
Image of page 3
  • Fall '15
  • Redox, atoms, Kwendo Alex

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern