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 concerning rounding and significant figures. 1. How can you identify if a reaction is a redox reaction or not? 2. Determine which of the following reactions are redox reactions. For each that is a redox reaction, identify any changes in oxidation number. 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 2 3. Assign oxidation numbers to each atom in the following substances. a. MnO 2 d. IO 3 b. S 8 e. HCO 3 c. CaCl 2 f. Fe 2 (SO 4 ) 3 4. Describe two different situations in which an oxygen atom can have oxidation number different from 2. 1
5. Explain the difference between oxidation and reduction. 6. Can a reaction contain an atom being oxidized but not one being reduced? Explain. 7. Oxidation numbers can be nonintegers. What is the oxidation number for each atom in S 4 O 6 2? 8. Consider the reaction: CuCl 2 (aq) + Mg(s) MgCl 2 (aq) + Cu(s) a. Identify the oxidation numbers for each atom in the reaction on the reactants side and on the products side. Reactant Product Cu Cl Mg b. What is being oxidized? c. What is being reduced? d. What is the oxidizing agent? e. What is the reducing agent? f. What is gaining electrons? g. What is losing electrons? h. How many electrons are being transferred? 9. Some redox reactions are called disproportionation reactions in which the same type of atom is both oxidized and reduced. Identify the changes in oxidation number in: Cl 2 + 2OH ClO + Cl + H 2 O. 2
10. Write the balanced (in terms of atoms and charges) halfreaction for each of the following descriptions. Identify each as either a reduction or oxidation. a. Iron (III) ions in solution change to solid iron b. Iodide ions in solution change to solid iodine c. Manganese (II) ions in solution change into permanganate ions d. Hypochlorite ions in solution change into chloride ion. e. Nitrate ions in solution create nitrogen monoxide gas. 11. When you are balancing a redox reaction, sometimes you need to multiply one or both of the halfreactions by an integer. Explain the purpose of this and why this must be done. 12. Balance each of the following redox reactions using the halfreaction method. Be sure to show all of your steps clearly. a. Br + Fe +3 Br 2 + Fe +2 b. MnO 4 + C 2 O 4 2 Mn +2 + CO 2 3
c. Cu + Ag + Ag + Cu +2 d. CrO 4 2 + Cl Cr +3 + Cl 2 e. Cr 2 O 7 2 + S 2 Cr +3 + S f. Mn +2 + Br 2 MnO 2 + Br g. Mn +2 + ClO MnO 4 + Cl 4
13. How can you measure the experimental voltage of a galvanic cell? 14. How do the electrons get transferred between the two containers in a galvanic cell? 15. For a galvanic cell, the cell potential must be. 16. Cell potential is measured in. 17. Why do we have to always reverse one of the halfreactions from the Reduction Potential Chart? 18. Because the chart contains Standard Reduction Potentials, what do we assume about the solutions and gases? 19. A student is creating a galvanic cell that would do the following reaction: Mn(s) + Sn +4 (aq) Mn +2 (aq) + Sn +2 (aq) a. The galvanic cell is created using two beakers connected with a wire by their electrodes. What are the two electrodes made of? Electrode A: Electrode B: b. What ions were in the solutions in each beaker? Beaker A: Beaker B: c. Which direction will the electrons move through the wire? d. Calculate the cell potential. 20. Explain the purpose of the salt bridge or porous disk. Why is it needed? 5
21. A student wants to create a galvanic cell using a large piece of copper, copper (II) nitrate solution, a large piece of chromium, and some chromium (III) nitrate solution. a. Write the two possible half reactions involving these substances. b. Which half reaction must be reversed to create a positive cell potential? c. Write the balanced reaction below. d. Calculate the cell potential. e. Sketch the galvanic cell below. Be sure label the solution and electrodes. f. Identify the cathode and anode. g. There should be a salt bridge connecting your beakers in (e). The salt bridge contains a NaNO 3 solution. Which direction are the nitrate ions moving in? 6