Oxidation-Reduction Reactions

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1 Chemistry Grade:12 CHAPTER 19 REVIEW Oxidation-Reduction Reactions SECTION 1 SHORT ANSWER Answer the following questions in the space provided. 1. All the following equations involve redox reactions except (a) CaO + H 2 O Ca(OH) 2. (b) 2SO 2 + O 2 2SO 3. (c) 2HgO 2Hg + O 2. (d) SnCl 4 + 2FeCl 2 2FeCl 3 + SnCl Assign the correct oxidation number to the individual atom or ion below. a. Mn in MnO 2 b. S in S 8 c. Cl in CaCl 2 d. I in e. C in IO 3 HCO 3 f. Fe in Fe 2 (SO 4 ) 3 g. S in Fe 2 (SO 4 ) 3 3. In each of the following half-reactions, determine the value of x. a. S 6+ + x e S 2 b. 2Br x Br 2 + 2e c. Sn e Sn x d. Which of the above half-reactions represent reduction processes? 4. Give examples, other than those listed in Figure 1.1 of the text, for the following: Answers may vary. a. a compound containing H in a 1 oxidation state b. a peroxide c. a polyatomic ion in which the oxidation number for S is +4 d. a substance in which the oxidation number for F is not 1 Modern Chemistry 2 Oxidation-Reduction Reactions

2 SECTION 1 continued 5. OILRIG is a mnemonic device often used by students to help them understand redox reactions. Oxidation is loss, reduction is gain. Explain what that phrase means loss and gain of what? 6. For each of the reactions described by the following equations, state whether or not any oxidation and reduction is occurring, and write the oxidationreduction half-reactions for those cases in which redox does occur. a. Ca(OH) 2 (aq) + 2HCl(aq) CaCl 2 (aq) + 2H 2 O(l) b. CH 4 (g) + 2O 2 (g) CO 2 (g) 2H 2 O(g) c. 2Al(s) + 3CuCl 2 (aq) 2AlCl 3 (aq) + 3Cu(s) 7. I is converted into I 2 by the addition of an aqueous solution of KMnO4 to an aqueous solution of KI. a. What is the oxidation number assigned to I 2? b. The conversion of I to I 2 is a(n) reaction. c. How many electrons are lost when 1 mol of I 2 is formed from I? Modern Chemistry 3 Oxidation-Reduction Reactions

3 CHAPTER 19 REVIEW Oxidation-Reduction Reactions SECTION 2 SHORT ANSWER Answer the following questions in the space provided. 1. All of the following should be done in the process of balancing redox equations except (a) adjusting coefficients to balance atoms. (b) adjusting coefficients in electron equations to balance numbers of electrons lost and gained. (c) adjusting subscripts to balance atoms. (d) writing two separate electron equations. 2. MnO 4 can be reduced to MnO 2. a. Assign the oxidation number to Mn in these two species. b. How many electrons are gained per Mn atom in this reduction? c. If 0.50 mol of MnO 4 is reduced, how many electrons are gained? 3. Iodide ions can be oxidized to form iodine. Write the balanced oxidation halfreaction for the oxidation of iodide to iodine. 4. Some bleaches contain aqueous chlorine as the active ingredient. Aqueous chlorine is made by dissolving chlorine gas in water. Aqueous chlorine is capable of oxidizing iron(ii) ions to iron(iii) ions. When iron(ii) ions are oxidized, chloride ions are formed. a. Write equations for the two half-reactions involved. Label them oxidation or reduction. b. Write the balanced ionic equation for the redox reaction between aqueous chlorine and iron(ii). c. Show that the equation in part b is balanced by charge. Modern Chemistry 4 Oxidation-Reduction Reactions

4 SECTION 2 continued 5. Write the equations for the oxidation and reduction half-reactions for the redox reactions below, and then balance the reaction equations. a. MnO 2 (s) + HCl(aq) MnCl 2 (aq) + Cl 2 (g) + H 2 O(l) b. S(s) + HNO 3 (aq) SO 3 (g) + H 2 O(l) + NO 2 (g) c. H 2 C 2 O 4 (aq) + K 2 CrO 4 (aq) + HCl(aq) CrCl 3 (aq) + KCl(aq) + H 2 O(l) + CO 2 (g) Modern Chemistry 5 Oxidation-Reduction Reactions

5 CHAPTER 19 REVIEW Oxidation-Reduction Reactions SECTION 3 SHORT ANSWER Answer the following questions in the space provided. 1. For each of the following, identify the stronger oxidizing or reducing agent. (Refer to Figure 3.2 of the text.) a. Ca or Cu as a reducing agent b. Ag + or Na + as an oxidizing agent c. Fe3 + or Fe 2+ as an oxidizing agent 2. For each of the following incomplete equations, state whether a redox reaction is likely to occur. (Refer to Figure 3.2 of the text.) a. Mg + Sn 2+ b. Ag + Cu 2+ c. Br 2 + I 3. Label each of the following statements about redox as True or False. a. A strong oxidizing agent is itself readily reduced. b. In disproportionation, one chemical acts as both an oxidizing agent and a reducing agent in the same process. c. The number of moles of chemical oxidized must equal the number of moles of chemical reduced. 4. Solutions of Fe 2+ are fairly unstable, in part because they can undergo disproportionation, as shown by the following unbalanced equation: a. Balance the above equation. Fe 2+ Fe 3+ + Fe b. If the reaction described above produces mol of Fe, how many moles of Fe 3+ will form? Modern Chemistry 6 Oxidation-Reduction Reactions

6 SECTION 3 continued 5. Oxygen gas is a powerful oxidizing agent. a. Assign the oxidation number to O 2. b. What does oxygen s oxidation number usually become when it functions as an oxidizing agent? c. Approximately where would you place O 2 in the list of oxidizing agents in Figure 3.2 of the text? d. Describe the changes in oxidation states that occur in carbon and oxygen, and identify the oxidizing and reducing agents, in the combustion reaction described by the following equation: C 6 H 12 O 6 (s) + 6O 2 (g) 6CO 2 (g) + 6H 2 O(l) 6. An example of disproportionation is the slow decomposition of aqueous chlorine, Cl 2 (aq), represented by the following unbalanced equation: Cl 2 (aq) + H 2 O(l) ClO (aq) + Cl (aq) + H + (aq) a. Show that the oxygen and hydrogen atoms in the above reaction are not changing oxidation states. b. Show the changes in the oxidation states of chlorine as this reaction proceeds. c. In the oxidation reaction, how many electrons are transferred per Cl atom? d. In the reduction reaction, how many electrons are transferred per Cl atom? e. What must be the ratio of ClO to Cl in the above reaction? Explain your answer. f. Balance the equation for the decomposition of Cl 2 (aq). Modern Chemistry 7 Oxidation-Reduction Reactions

Name Period Date. Ch. 19: Oxidation-Reduction Reactions Homework

Name Period Date. Ch. 19: Oxidation-Reduction Reactions Homework Name Period Date Ch. 19: OxidationReduction Reactions Homework Answer each of the following questions in as much detail as you can. Be sure to show all your work for any calculations and follow all rules