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Chapters 17 (17.1 – 17.3): Instrumental Methods in Electrochemistry We use electrochemistry to do analytical chemistry in a variety of ways. We’ve already talked about pH electrodes and other kinds of ISE. Here are some more examples. Electrogravimetric Analysis The ______________________ part means we’ll be using weighing as part of this analysis. This method involves ____________________ _______ the analyte onto an electrode. For example, copper: This figure shows how it would be done:

Example. A 10.00 mL of Cr3+ was electrolyzed to deposit all the chromium on the cathode. The mass of the cathode was 15.222 g before the electrolysis and 17.132 g after the electrolysis. What was the molarity of Cr3+ in the unknown?

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Coulometry In this method, ___________________ are counted to determine how much analyte reacted. q = F = For example,

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Amperometry This method uses current to drive an _______________________ reaction; we measure how much current is used. The ________________ is held current while we measure the __________________. An example of this is a ______________________ ___________________ electrode. This kind of electrode can fit into the tip of a surgical catheter to measure DO in the umbilical artery of a newborn child and detect respiratory illness; it has a response time of Another example is a ________________________ _______________________.

Potential interferences include: Why don’t users have to construct a calibration curve every time they use it?

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Voltammetry In this method, current is measured while the ___________________ between two electrodes is varied. For example, we can measure ascorbic acid in fruit drinks.

Oxidation of the ascorbic acid takes place on what we call the ____________________ electrode. Reduction of H+ occurs at the other electrode which is called the __________________ Electrode. While the voltage varies, our computer records a ______________________________. Here’s what the voltammogram looks like:

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The _______________ _________________________ is proportional to the __________________________ of ascorbic acid in the sample. This is a good method for using __________________ ______________________. From page 114, “Ask Yourself” problem 5C on page 114: Successive standard additions of 1.00 mL of 25.0 mM ascorbic acid were made to 50.0 mL of orange juice. Find the concentration of ascorbic acid in the orange juice.

[Sf]  (mM)  

Peak  Current  (μA)  

 0   1.66  0.500   2.03  1.00   2.39  1.50   2.79  2.00   3.16  2.50   3.51  

[Sf]  =  [Si]V/V0  (mM)  

Corrected  Peak  

Current  (μA)  

0   1.66  0.50   2.07  1.00   2.49  1.50   2.96  2.00   3.41  2.50   3.86  

Homework: Chapter 5 # 20; Chapter 17 # 6, 8, 25