Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
CHAPTER 4 4.10 – Balancing Redox Reactions: The HalfReaction Method Oxidation numbers Oxidation Number (State): A value which indicates whether an atom is neutral, electron-rich, or electron-poor. Rules for Assigning Oxidation Numbers 1. 2. 3. 4. 5. An atom in its elemental state has an oxidation number of 0. A monatomic ion has an oxidation number identical to its charge An atom in a polyatomic ion or in a molecular compound usually has the same oxidation number it would have if it were a monatomic ion 1. Hydrogen can be either +1 or – 2. Oxygen usually has an oxidation number of -2 Halogens usually have an oxidation number of -1 The sum of the oxidation numbers is 0 for a neutral compound and is equal to the net charge for a polyatomic ion Ch apt er 4/2 Writing the half Oxidation and Reduction Reactions Write the separate half oxidation and reduction reactions for the following equation. 2Cs(s) + F2(g) 2CsF(s) 3 Balancing Redox Reaction using half equation in an Acidic Solution 1. Assign oxidation numbers to each atom from the given unbalanced equation 2. Split the equation into half-reaction 3. Complete and balance each half reaction ◦ Balance all atoms except O and H ◦ Balance oxygen atoms by adding H2O to one side of the equation ◦ Balance hydrogen atoms by adding H+ ions to one side of the equation ◦ Balance the number of electrons being transferred 4. Combine the half-reaction to obtained the final balanced equation ◦ The electrons must be cancelled ◦ Simplify the equation by reducing coefficients and canceling repeated species ◦ After you’re done, double check your balanced equation Example Balance the following net ionic equation in acidic solution: I1-(aq) + Cr2O72-(aq) Cr3+(aq) + IO31-(aq) Additional steps for balancing equations in basic solution Follow all steps from the acidic solution ( 1 4) Add the desired number of –OH react with H+ ions in the reaction; add to both side of the reaction. This is a neutralization step ◦ Simplify the equation by noting that H+ combines with –OH to give H2O ◦ Cancel any repeating H2O and –OH ions and reduce reaction to the lowest coefficients Balancing Redox Reactions: The HalfReaction Method Balance the following net ionic equation in basic solution: MnO41-(aq) + Br1-(aq) MnO2(s) + BrO31-(aq) Example Balance the following net-ionic equation by the half-reaction method. ◦ Cu(s) + NO3-(aq) Cu2+(aq) + NO2(g) Acidic condition ◦ I-(aq) + MnO4-(aq) I2(aq) + MnO2(g) Condition ◦ Fe(OH)2(s) + O2(g) Fe(OH)3(s) Basic Basic condition