CHEM 1B Lecture Notes - Lecture 12: Reduction Potential, Electrochemistry, Burette

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1 Jun 2020

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UCSB

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Chemistry and Biochemistry

Course

CHEM 1B

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Kunkel

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CHEM 1B Full Course Notes

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The purpose of this experiment was to study the effects of temperature on the concentration of cell potentials. In part 1, the standard reduction potential, e , of ag, cu, fe, and. Zn were measured with reference to hydrogen, copper, and silver electrodes. These results are displayed in a table below, as was given in the data sheet provided for this experiment. In part 2 of this experiment, solid aluminum was reacted with cucl2. It was observed that the aluminum disintegrated in the cucl2 solution, and the solution turned into a reddish-orange color. The reaction was exothermic, as heat was released in the form of bubbles. The equation and cell potential are shown below. In part 3 of this experiment, copper was reacted with agno3. It was observed that the copper reacted with the agno3, and that the latter became a solid around the copper coil. The reaction is exothermic, since heat is a product.

Related Questions

1) Using the standard reduction potentials table in your book/notes, what is the standard change in gibbs free energy for the following reaction in kJ?

2NO₃^-(aq) + 8H⁺(aq) + 3Cu(s) â 3Cu²⁺(aq) + 2NO(g) + 4H₂O(l)

If you took CHEM 122 lab here, this was the first reaction in the cycle of copper lab that released the brown NO gas.

2) What is the value of K at 298K for the following reaction? (Please give your answer to two significant digits in scientific notation) K = e^nFEÂ°/RT

3A²⁺(aq) + 2B(s)â 2B³⁺(aq) + 3A(s)

A²⁺(aq) + 2e^- â A(s) EÂ°_red = â0.58 V

B³⁺(aq) + 3e^- â B(s) EÂ°_red = â 0.75 V

3) What is the cell potential for the spontaneous concentration cell with the reaction Fe³⁺(aq) + Fe(s) â Fe(s) + Fe³⁺(aq), with concentrations of Fe³⁺ of 0.848M and 0.353M at a temperature of 310. K?

E_cell = EÂ°_cell â(RT/nF)lnQ

4) Which of the following will increase the cell potential for the following reaction:

2Fe³⁺(aq) + 3Zn(s) â 3Zn²⁺(aq) + 2Fe(s)

Use the reaction E_cell = EÂ°_cell â (RT/nF)lnQ and consider how each manipulation affects Q and thus affects E_cell

_{- Add zinc solid}

_{- Remove water from the entire system}

- Add solid iron to the system

- Increase the concentration of zinc ion in solution

- Dilute the entire system

- Increase the concentration of Fe3+ in the solution

A) What is the value of K at 298K for the following reaction? (Please give your answer to two significant digits in scientific notation) K = e^nFEÂ°/RT

3A²⁺(aq) + 2B(s)â 2B³⁺(aq) + 3A(s)

A²⁺(aq) + 2e^- â A(s) EÂ°_red = â0.45 V

B³⁺(aq) + 3e^- â B(s) EÂ°_red = â 0.75 V

B) Using the standard reduction potentials table in your book/notes, what is the standard change in gibbs free energy for the following reaction in kJ?

2NO₃^-(aq) + 8H⁺(aq) + 3Cu(s) â 3Cu²⁺(aq) + 2NO(g) + 4H₂O(l)

If you took CHEM 122 lab here, this was the first reaction in the cycle of copper lab that released the brown NO gas.

C) What is the cell potential for the spontaneous concentration cell with the reaction Fe³⁺(aq) + Fe(s) â Fe(s) + Fe³⁺(aq), with concentrations of Fe³⁺ of 0.858M and 0.328M at a temperature of 310. K?

E_cell = EÂ°_cell â(RT/nF)lnQ

D)Which of the following will decrease the cell potential for the following reaction:

2Fe³⁺(aq) + 3Zn(s) â 3Zn²⁺(aq) + 2Fe(s)

Use the reaction E_cell = EÂ°_cell â (RT/nF)lnQ and consider how each manipulation affects Q and thus affects E_cell

		Dilute the entire system
		Remove water from the entire system
		Add solid iron to the system
		Increase concentration of Fe³⁺ in the solution
		Increase the concentration of zinc ion in solution
		Add zinc solid

You are asked to construct a voltaic cell that would simulate an alkaline battery by providing an electrical output of 1.50 VV at the beginning of its discharge. After you complete it, your voltaic cell will be used to power an external device that draws a constant current of 0.50 AA (amperes) for 2.0 hh. You are given the following supplies: electrodes of each transition metal from manganese to zinc; the chloride salts of the +2 transition metal ions from Mn2+Mn2+ to Zn2+Zn2+ (MnCl2MnCl2, FeCl2FeCl2, CoCl2CoCl2, NiCl2NiCl2, CuCl2CuCl2, and ZnCl2ZnCl2); two 100 mLmL beakers; a salt bridge; a voltmeter; and wires to make electrical connections between the electrodes and the voltmeter. The standard reduction potentials for the divalent metal ions are as follows: Half-reactionMn2+(aq)Fe2+(aq)Co2+(aq)Ni2+(aq)Cu2+(aq)Zn2+(aq)++++++2e−2e−2e−2e−2e−2e−→→→→→→Mn(s)Fe(s)Co(s)Ni(s)Cu(s)Zn(s)E∘(V)−1.18−0.44−0.28−0.250.34−0.76 Since you were tasked with constructing a cell that produces a potential of 1.50 VV, you decide to fine tune your concentrations to minimize the error. If you used the same concentration for each electrolyte, your voltaic cell would produce a potential of 1.52 VV. Therefore, you should adjust the concentration ratio that would lower your cell potential by 0.02 VV. You and a fellow researcher decide that you should prepare two 100 mLmL solutions for the voltaic cell. Your fellow researcher already prepared one of the electrolyte solutions for you: 0.228 MM CuCl2 CuCl2. At what concentration should you prepare the MnCl2MnCl2 solution such that your initial voltaic cell potential is 1.50 VV? Assume that the temperature is consistently 25 ∘C∘C. If the battery is permitted to discharge for a period of two hours at a constant current of 0.50 AA, what will be the concentration of the manganese(II) ion in the anode electrolyte solution at the end of the discharge? Similarly, what will be the concentration of the copper(II) ion in the cathode electrolyte solution at the end of the discharge? Given the nature of how a cell is constructed, you would usually deplete the ions at the cathode before completely oxidizing the anode (since the latter would break the circuit). This is because the complete oxidation of the anode would likely only occur if you were using an extremely thin wire of the metal. In this case, let us assume you constructed the voltaic cell using sufficiently sized rods for each metal. This means that the total time you can run your cell will depend on the initial copper ion concentration. Calculate the maximum run time for your voltaic cell if it runs at 0.5 AA and your initial concentration of CuCl2(aq)CuCl2(aq) was 0.228 M'

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CHEM 1B Lecture Notes - Lecture 12: Reduction Potential, Electrochemistry, Burette

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