Electrochemistry, Concentration and Cell Potential Electrochemistry involved oxidation and reduction

Electrochemistry, Concentration and Cell Potential

Electrochemistry involved oxidation and reduction reactions An oxidation reactioninvolves the loss of electrons (creating a more positive charge), whereas a reduction reactioninvolves the gain of electrons (creating a more negative charge) Redox reactions deal with the transfer of electrons between the materials being reacted, then leaving a residual charge once reacted When calculating total cell potential, the potential values of both the anodeand the cathodemust be determined Once that occurs, the formula below can be utilized to determine your E°cell value

E°cell = E°Anode + E°Cathode

At the anode (the negative electrode), oxidation occurs with a loss of electrons, creating a more positive charge on the anode At the cathode (the positive electrode, reduction occurs with a gain of electrons, creating a more negative charge This gain and loss of electrons can be expressed through half-cell reactionsand standard cell notation A half-cell reaction shows the gain or loss of electrons of a single system, whereas standard cell notation encapsulates both the anode and cathode and the electron transfers separated by a salt bridge (denoted by a double vertical bar in between ||) An example of a half-cell and a standard cell notation is outlined below Be sure to note that the anode is always listed first in standard cell notation

Overall Chemical Reaction2 Ag+(aq) + Cd(s) ? Cd2+(aq) + 2 Ag(s) Half-Cell Reaction (Anode)Cd(s) ? Cd2+(aq) + 2e-

Half-Cell Reaction (Cathode)2 Ag+(aq) + 2e- ? 2 Ag(s) Standard Cell NotationCd(s)| Cd2+(aq, 015 M) || Ag+(aq, 020 M) | Ag(s)

Rowan University/Fall 2017/Department of Chemistry and Biochemistry

Rowan University/Fall 2017/Department of Chemistry and Biochemistry Please note that your work will be completed based on completeness and correctness Be sure to

read each set of directions carefully

PART ONE:Use the data below to perform the calculations and tabulations needed

When conducting an electrochemistry laboratory exercise with your lab partner, you made multiple solutions of different concentrations of Copper Nitrate The concentrations that you made were 005 M, 010 M, 020 M, 050 M and 075 M, respectively by first calculating the dilution factors and diluting a 100 M stock solution accordingly An apparatus was made with a plastic cup assembly, a porous cup acting as the salt bridge, a stock 100 M Lead Nitrate, a copper electrode and a lead electrode The lead nitrate was placed inside of the salt bridge cup with the lead electrode and placed inside of the plastic cup assembly; each copper nitrate solution was then poured into the plastic cup, between the plastic cup and the porous salt bridge accompanying the copper electrode The voltage readings were recorded below:

Concentration of Copper Nitrate (M)

005

0012

010

00175

020

E°cell Reading (V)

0022

050

0040

075

0052

1 On a separate piece of paper, make a plot of the data above showing the concentration of Copper Nitrate vs the E°cell Reading Note the kind of relationship Provide a figure caption, axis labels, and a chart title

2 Suppose you were to conduct the same experiment but with a solution with an unknown concentration The voltage reading you recorded for the unknown was 0047 V With this information, draw a line of best fit of the data in question one From the line of best fit, determine the estimated molarity of the unknown solution and record it here: ____________

PART TWO:Nernst Equation

The Nernst Equation is a method of calculating cell potential by using the standard cell potential (E°cell), gas constant (8315 J/mol K), temperature in Kelvin (T), number of moles of electrons transferred during the reaction (n), Faraday’s constant (F = 96485335 C/mol), and the reaction quotient (Q) The equation is as follows:

Ecell = E°cell – (RT/nF)*ln(Q)

1 Calculate the cell potential of a galvanic cell made of lead and cadmium The molarity of the cadmium solution was 0200 M, and the molarity of the lead solution was 0100 M The temperature of the cell is 300 K

Cd?Cd2+ +2e- E°=+0403V Pb2+ +2e- ?Pb E°=-0126V

E°cell = _____________________

2 Calculate E°cell of a cell made of zinc and copper The molarity of the copper solution is 0300 M, the molarity of the zinc solution is 0150 M, Ecell is 148 V, and the temperature of the cell is 325 K

Rowan University/Fall 2017/Department of Chemistry and Biochemistry

Rowan University/Fall 2017/Department of Chemistry and Biochemistry

PART THREE: Standard Cell Notation and Half Reactions

Write the Standard Cell Notation and Half Reactions of the following voltaic cell combinations

1 Zinc Nitrate (020 M) and Copper Nitrate (030 M); Copper – Anode, Zinc – Cathode

2 Lead Sulfate (025 M) and Zinc Sulfate (050 M); Lead – Cathode, Zinc – Anode

3 Copper Sulfate (065 M) and Lead Sulfate (020 M); Copper – Anode, Zinc – Cathode

4 Silver Nitrate (015 M) and Lead Nitrate (040 M); Silver – Anode, Lead – Cathode

5 Aluminum Nitrate (035 M) and Silver Nitrate (050); Aluminum – Anode, Silver – Cathode

6 Copper Nitrate (045 M) and Silver Nitrate (025 M); Copper – Anode, Silver – Cathode

 

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