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NCSU CH 202 - Lab 10 Postlab

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1. 13.5/13.5 points Last Response | Show Details All Responses Notes Complete the following table. The measured potentials are your experimental data. Use the table of Standard Reduction Potentials. to determine the calculatedpotentials. Use the Zn2+/Zn potential as the reference in each case. Please enter your potentials in volts. Hint: Use the Nernst Equation where necessary. The percent difference is defined as: [ (Calculated Potential - Measured Potential) / Calculated Potential ] x 100. Note that, defined in this way, percent differences can be positive or negative. Cell Measured Potential Calculated Potential % differenceAg-Zn1.27 [1.27]V 1.53 [1.53]V 16.99 [17]Pb-Zn.381 [0.381]V .63 [0.63]V 39.52 [39.5]Cu-Zn.869 [0.869]V 1.10 [1.10]V 21 [21]2. 4/4 points Last Response | Show Details All Responses Notes If you wanted to shift the potential of the lead-zinc cell upward, toward 0.70 V, which of the following actions would give the desired result? Check all that apply. [x] [x] Any action that makes [Zn2+] smaller than [Pb2+]. [x] [x] Any action that makes Q < 1.0. [_] [_] Any action that makes [Zn2+] larger than [Pb2+]. [x] [x] Any action that makes log Q negative. [x] [x] Adding some concentrated Pb(C2H3O2)2 solution to the Pb2+/Pb couple. [_] [_] Any action that makes Q > 1.0. [_] [_] Any action that makes log Q positive. [_] [_] Adding some concentrated Zn(C2H3O2)2 solution to the Zn2+/Zn couple.3. 4/4 points Last Response | Show Details All Responses Notes If you measured a shift in the copper / ascorbic acid cell potential when the pH was changed, what was the origin of the shift? In other words, which half-cell potential was actually changing, the copper potential, the ascorbic acid potential, or both? Select all true statments. [_] [_] The pH change caused a difference in the rate of electron transfer which shifted the potential of the Cu2+/Cu half-cell.[x] [x] The Cu2+/Cu half-cell did not have a role in the potential change. [x] [x] The ascorbic acid half-reaction contains two H1+ ions. [x] [x] When pH changes, the value of Q changes. [_] [_] Both half-cells experienced potential shifts when the ph was changed. [x] [x] The reaction quotient contains a term for [H1+]. [x] [x] The potential change was due to the pH change in the ascorbic acid half-cell.4. 3.5/3.5 points Last Response | Show Details All Responses Notes Consider, again, the copper / ascorbic acid cell. a. What potential, in volts, did you measure for the cell at pH 5? .214 [0.214] Vb. What is the potential, in volts, of the ascorbic acid half cell at pH 5 vs. the standard hydrogen half cell? Hint: Think about which was the reference (anode). .126 [0.126]


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NCSU CH 202 - Lab 10 Postlab

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