Sample Exercise 20.2 Practice Exercise 1 with feedback

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1 Homework Chapter 20 Due: 11:59pm on Wednesday, November 16, 2016 You will receive no credit for items you complete after the assignment is due. Grading Policy Sample Exercise 20.2 Practice Exercise 1 with feedback Balancing Redox Equations in Acidic Solution If you complete and balance the following equation in acidic solution how many water molecules are there in the balanced equation (for the reaction balanced with the smallest whole number coefficients)? M n 2+ (aq) + NaBi O 3 (s) B i 3+ (aq) + Mn O 4 (aq) + N a + (aq) Four on the reactant side One on the reactant side Two on the product side Three on the product side Seven on the product side The balanced equation for the reaction in acidic solution is 14 H + (aq) + 2 M n 2+ (aq) + 5 NaBi O 3 (s) 2 Mn O 4 (aq) + 5 B i 3+ (aq) + 5 N a + (aq) + 7 H 2 O(l) There are 7 water molecules on the product side. Sample Exercise 20.3 Practice Exercise 1 with feedback Balancing Redox Equations in Basic Solution If you complete and balance the following oxidation reduction reaction in basic solution how many hydroxide ions are there in the balanced equation (for the reaction balanced with the smallest whole number coefficients)? N O 2 (aq) + Al(s) N H 3 (aq) + Al(OH ) 4 (aq) One on the reactant side One on the product side Four on the reactant side Seven on the product side None 1/9

2 The balanced equation for the reaction in basic solution is 2 Al(s) + N O 2 (aq) + O H (aq) + 5H 2 O(l) N H 3 (aq) + 2Al(OH ) 4 (aq) There is 1 hydroxide molecule on the reactant side. Give It Some Thought 20.2 Do free electrons appear anywhere in the balanced equation for a redox reaction? Yes, free electrons appear in the right part of the equation. Yes, free electrons appear in the left part of the equation. Yes, free electrons appear in the both parts of the equation. No, free electrons do not appear in the balanced equation for a redox reaction. Sample Exercise 20.4 Practice Exercise 1 with feedback Describing a oltaic Cell The following two half reactions occur in a voltaic cell: Ni(s) Cu 2+ (aq) + 2 Ni 2+ (aq) + 2 Cu(s) (electrode = Ni) (electrode = Cu) Which one of the following descriptions most accurately describes what is occurring in the half cell containing the Cu electrode and C u 2+ (aq) solution? The electrode is gaining mass and anions from the salt bridge are flowing into the half cell. The electrode is gaining mass and cations from the salt bridge are flowing into the half cell. The electrode is losing mass and anions from the salt bridge are flowing into the half cell. The electrode is losing mass and cations from the salt bridge are flowing into the half cell. 2/9

3 Sample Exercise 20.5 Practice Exercise 1 with feedback Calculating Ered from Ecell A voltaic cell based on the reaction 2 E u 2+ (aq) + N i 2+ (s) 2 E u 3+ (aq) + Ni(s) generates Ecell = Given the standard reduction potential of Ni 2+ ( Ered = 0.28 ) what is the standard reduction potential for the reaction E u 3+ (aq) + E u 2+ (aq)? Sample Exercise 20.7 Practice Exercise 1 with feedback Determining Half Reactions at Electrodes and Calculating Cell Potentials There are three voltaic cells. In each voltaic cell one half cell contains a 1.0 M Fe(N O 3 ) 2 (aq) solution with an Fe electrode. The contents of the other half cells are as follows: Cell 1: a 1.0 M CuC l 2 (aq) solution with a Cu electrode Cell 2: a 1.0 M NiC l 2 (aq) solution with a Ni electrode Cell 3: a 1.0 M ZnC l 2 (aq) solution with a Zn electrode In which voltaic cell(s) does iron act as the anode? Cell 1 Cell 2 Cell 3 Cells 1 and 2 All three cells The standard reduction potential of the Fe 2+ /Fe half cell is So, it would be the anode if the other cell had a greater standard reduction potential. So, the Fe 2+ /Fe half cell would act as the anode in cell 1 and cell /9

4 Problem A voltaic cell consists of a strip of cadmium metal in a solution of Cd(N O 3 ) 2 in one beaker, and in the other beaker a platinum electrode is immersed in a NaCl solution, with Cl 2 gas bubbled around the electrode. A salt bridge connects the two beakers. Which electrode serves as the anode, and which as the cathode? Pt serves as the cathode, Cd as the anode. Cd serves as the cathode, Pt as the anode. Part B Does the Cd electrode gain or lose mass as the cell reaction proceeds? The The Cd Cd electrode will gain mass as the cell reaction proceeds. electrode will lose mass as the cell reaction proceeds. Part C Write the equation for the overall cell reaction. Express your answer as a chemical equation. Identify all of the phases in your answer. C l 2(g) + Cd (s) C d 2+ (aq) + 2Cl (aq) Part D What is the emf generated by the cell under standard conditions? Express your answer using four significant figures. E = /9

5 Sample Exercise 20.9 Practice Exercise 1 with feedback Determining Spontaneity Using a table of standard reduction potentials, select the following elements that are capable of oxidizing F e 2+ (aq) ions to Fe 3+ (aq) ions: oxygen, chlorine, bromine, iodine? Check all that apply. I 2 O 2 Cl 2 Br 2 Only two of these elements are capable of oxidizing Fe 2+ (aq). The elements that can oxidize Fe 2+ (aq) have a more positive standard reduction potential than the Fe 3+ (aq) + Fe 2+ (aq) standard potential. Problem Consider the voltaic cell illustrated in the figure, which is based on the cell reaction Zn(s) + Cu 2+ (aq) Zn 2+ (aq) + Cu(s). Under standard conditions, what is the maximum electrical work, in joules, that the cell can accomplish if 52.0 g of copper is plated out? 5/9

6 Wmax = J Sample Exercise Practice Exercise 1 with feedback Cell Potential under Nonstandard Conditions Consider a voltaic cell whose overall reaction is Pb 2+ (aq) + Zn(s) Pb(s) + Zn 2+ (aq). What is the emf generated by this voltaic cell when the ion concentrations are [ Pb 2+ ] = M and [ Zn 2+ ] = 0.55 M? Sample Exercise Practice Exercise 1 with feedback Determining ph Using a Concentration Cell A concentration cell constructed from two hydrogen electrodes, both with PH 2 = One electrode is immersed in pure H 2 O and the other in 6.0 M hydrochloric acid. What is the emf generated by the cell and what is the identity of the electrode that is immersed in hydrochloric acid? 0.23, cathode 0.023, anode 0.23, cathode 0.46, cathode 0.23, anode Give Typesetting It Some math: 100% Thought /9

7 Based on the values in the table given below, which of these metals could provide cathodic protection to iron? TABLE Standard Reduction Potentials in Water at 25 C E red () [defined] Reduction Half Reaction F 2 (g) F (aq) MnO 4 (aq) + 8 H + (aq) + 5 Mn 2+ (aq) + 4 H 2 O(l) Cl 2 (g) Cl (aq) Cr 2 O 2 7 (aq) + 14 H + (aq) Cr 3+ (aq) + 7 H 2 O(l) O 2 (g) + 4 H + (aq) H 2 O(aq) Br 2 (l) Br (aq) NO 3 (aq) + 4 H + (aq) + 3 NO(g) + 2 H 2 O(l) Ag + (aq) + Ag(s) Fe 3+ (aq) + Fe 2+ (aq) O 2 (g) + 2 H + (aq) + 2 H 2 O 2 (aq) MnO 4 (aq) + 2 H 2 O(l) + 3 MnO 2 (s) + 4 OH (aq) I 2 (s) I (aq) O 2 (g) + 2 H 2 O(l) OH (aq) Cu 2+ (aq) + 2 Cu(s) 2 H + (aq) + 2 H 2 (g) Ni 2+ Fe 2+ Zn 2+ (aq) + 2 (aq) + 2 (aq) + 2 Ni(s) Fe(s) Zn(s) 2 H 2 O(l) + 2 H 2 (g) + 2 OH (aq) Al 3+ Na + Li + (aq) + 3 (aq) + (aq) + Al(s) Na(s) Li(s) Check all that apply. Cu Al Ni Zn 7/9

8 Problem Bars of iron are put into each of the three beakers as shown here. In which beaker A, B, or C would you expect the iron to show the most corrosion? Beaker A Beaker B Beaker C Problem Elemental calcium is produced by the electrolysis of molten CaCl 2. What mass of calcium can be produced by this process if a current of 5600 A is applied for 55 h? Assume that the electrolytic cell is 59 % efficient. Express your answer using two significant figures. m = g Ca Part B 8/9

9 What is the minimum voltage needed to cause the electrolysis? Express your answer using three significant figures. E C = 4.23 Score Summary: Your score on this assignment is 0%. You received 0 out of a possible total of 0 points. 9/9