Question

Pre Lab : Electrochemistry

ELECTROCHEMISTRY PRE-LAB ASSIGNMENT: Use the data given below to do similar calculations as you will be performing in today's lab Part A: Verification of the Nernst equation The electrochemical cell to be used can be represented using conventional cell notation as: Ag(s) l Agcl(s) HCII M)|Ce(aq),Ce (a) Pts) [Ce4+]-0. | 0 M [Ce3+]-0. I 0 M Room temperature 21.6°C voltage(m V Solution mL of Ce+ solution mL of Ces solution 25.0 25.0 25.0 25.0 25.0 24.0 15.0 5.0 1.0 1.0 5.0 15.0 24.0 25.0 25.0 25.0 25.0 25.0 1309 1348 1377 1385 1389 1392 1402 4 1428 1472 Part B: Electrolysis: mass of copper anode before electrolysis 21.0068 g mass of copper anode after electrolysis 20.8562 g aia-558 seconds DISCESSTON Part A: War the Nernst Equation vwerfied ho o slope and intercept to she Part A- Verification of the Nernst equation In this part of the experiment, we will verify that the Nernst equation correctly predicts the change in cell emf with changes in concentration of electrolyte. The voltage of an electrochemical cell will be measured using a pH meter which will he set up to read millivolts. The advantage of using this method of measuring cell voltage over a voltmeter is that the pH meter does not draw current from the cell and therefore the maximum voltage obtainable from the ceill will be measured. (This voltage is referred to as the reversible cell emf.) The electrochemical cell to be used can be represented using conventional cell notation as: The anode reaction involves the conversion of solid silver and chloride ion to silver chloride. This is a common half-reaction to use in reference electrodes: Ag(s) + CI (aq, 1 M) AgCI(s) + e The cathode reaction involves the reduction of Fe to Fe Fe Fe+ (in 1 M H so,) +0.68 v (Reference. Analytical Chemistry, Pietrzyk and Frank (2nd edition) Ifthe chloride ion concentration in the anode is held constant at 1 M, the only reason the cell voltage will change is because of changes in the cathode half-reaction ion concentrations: 2.303RT [Fe+] lo A predicted valuc for total may be found in the usual way (by adding the anode and cathode reaction voltages). PROCEDURE Prepare the solutions shown in Table 1 below using the stock solutions of Fe and Fe), Use burettes to measure the volumes required. Prepare your solutions in 100 mL beakers. For each solution, measure the voltage of the cell. Do not attempt to use the pH meter/voltmeter without first receiving instruction in its operation. Measure the temperature of sol assume all solutions are at this temperature. ution 5 and The electrodes are VERY IERACUD Table 1. Solutions to verify the Nernst equation. Solution Vo. of Fe2+ solution Vol. of Fe+ solution 4m 25.0 mL 25.0 mL 25.0 mL 25.0 mL 25.0 mL 24.0 mL 15.0 mL 5.0 mL 1.0 mL 1.0 mL 2 15.0 mL 24.0 mL 25.0 mL 25.0 mL 25.0 mL 25.0 mL 25.0 mL Gon a) Draw a graph of ε vs. log[Fe2+/Fe3+] and verify that this is a straight line. b) Find the slope and y-intercept of the line in (a) and compare this with the values predicted by the Nernst equation for the balanced chemical equation taking place in this electrochemical cell

Answer 1

a) The graph of '$\epsilon$' versus Log[Fe²⁺/Fe³⁺] can be drawn as follows.

1.4 1.5 0.5 0.0 0.5 1.0

b) The equation of the above line: $\epsilon$ = -0.05807*Log[Fe²⁺/Fe³⁺] + 1.38911

The slope of the line is -0.058 V

Now, the y-intercept of the line is 1.389 V