Experimental values Cell potential of Fe/Cu .562 Cell potential of Zn/Fe .375 12

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Experimental values

Cell potential of Fe/Cu .562 Cell potential of Zn/Fe .375 124 Chemistry 106 Fe F You are working in groups of 2 Part 1: Constructing Galvanic Cells Cu Porous cup containing 20 mL of CuSO4 Caq0 150 mL beaker containing 20 mL Lo Connect to of Zn (NO3)(aq) Voltmeter Figure 16.2: Setup for a Galvanic Cell Focus Questions: 1) What are the cell potentials for the three galvanic cells? 2) Do the experimental values match the theoretical values? Experimental Procedure Fe, zn). Wash it with 1. Using sand paper, clean each metallic electrode (Cu, and deionized water, and wipe it dry 2. Assemble cell as shown in figure 10.2. voltage is negative 3. Set the voltmeter on 2 v and measure the cell potential. If the reverse the wire connections. Record the voltage to decimal places. 4. In the same way, construct the following two cells, and measure their cell potentials. Fe(s)lFe2 (aq, 1M)ll Cu2+(aq, 1M)ICu(s) 5 late the theoretical cell potentials for these three cells, and compare the values with the experimental ones. Experiment 16

Explanation / Answer

1) For the electrochemical system:

Zn | Zn2+ (1 M) || cu2+ |Cu (1 M)

Zn(s) + Cu2+ (aq) --> Zn2+(aq) + Cu(s)

Write the half-reactions for each process.

Zn(s) --> Zn2+ (aq) + 2 e-

Cu2+ (aq) + 2 e ---> Cu(s)

E0 reduction of Cu2+ = + 0.339 V

The standard reduction potential for the reverse of the oxidation reaction, so change the sign.

E0 reduction of Zn2+ = - 0.762 V

E0 oxidation of Zn = - ( - 0.762 V) = + 0.762 V.

Add the cell potentials together to get the overall standard cell potential 0.762 V + 0.339 V = 1.101V

Overall:               Zn(s) + Cu2+(aq) --> Zn2+(aq) + Cu(s)        Eo cell = + 1.101 V

2) Calculate the theoretical cell potential for the Fe| Fe2+(1 M)|| cu2+ |Cu

Fe2+(aq) + 2e- Fe(s) -0.440                              E0 ox. = - E0 red. = - (- 0.440 V) = + 0.440 V

Reduction:         Cu2+(aq) + 2 e---> Cu(s)              E0 red. = + 0.339 V

Add the cell potentials together to get the overall standard cell potential 0.440 V + 0.339 V = +779V

Overall:               Fe(s) + Cu2+(aq) --> Fe2+(aq) + Cu(s)        Eo cell = + 779 V

3) For the electrochemical system:

Zn | Zn2+ (1 M) || Fe2+ (1 M) | Fe

Oxidation Reaction Zn(s)--> Zn2+ (1 M) + 2 e E0 ox. = - E0 red. = - (- 0.762 V) = + 0.762 V

Fe2+(aq) + 2e- Fe(s)                 E0 red = -0.440 V

Add the cell potentials together to get the overall standard cell potential 0.762 V + - 0.440 V = 0.322V

Overall:               Zn(s) + Fe2+(aq) --> Zn2+(aq) + Fe(s)       Eo cell = + 0.322 V

Experimental value is lesser than the theoretical value in three cases. There are so many possible reasons for that low value.

i)-Resistance of the wires attached to electrode and the voltmeter have used will significantly lower down the potential.

ii) Purity of Fe, Zn and Cu will also affect.

iii) Cleaning the oxidized outer part of electrodes will also affect.

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