# Water is easier to oxidize than f and so 4 2 however

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Chapter 18 / Exercise 35
Chemistry
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Water is easier to oxidize than F - and SO 4 2- . However, the products predicted from this type of comparison of electrode potentials are NOT ALWAYS THE ACTUAL PRODUCTS! For gases such as H 2 (g) and O 2 (g) to be produced at metal electrodes, an additional voltage is required. This increment over the expected voltage is called the overpotential , and it is 0.4 to 0.6 V for these gases. The overpotential results from kinetic factors such as the large activation energy required for gases to form at the electrode.
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Chapter 18 / Exercise 35
Chemistry
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To summarize electrolysis, consider the following points : 1. Cations of less active metals are reduced to the metal; cations of more active metals are NOT reduced. That is, most transition metal cations are more readily reduced than water; water is more readily reduced than main group metals. 2. Anions that are oxidized because of overvoltage of O 2 formation include the halides (except F - ). 3. Anions that are NOT oxidized include F - and common oxoanions such as SO 4 2- , CO 3 2- , NO 3 - , and PO 4 3- because the central nonmetal in the oxoanions is already in its highest oxidation state.
Electrolysis of Mixtures 1. A sample of AlBr 3 was contaminated with KF then made molten and electrolyzed. Determine the products and write the overall cell reaction. 2. Suppose aqueous solutions of Cu 2+ , Ag + , & Zn 2+ were all in one container. If the voltage was initially low and then gradually turned up, in which order will the metals plate out onto the cathode? Ag + + e - Ag Cu 2+ + 2e - Cu Zn 2+ + 2e - Zn
Workshop on Electrolysis : 1. Write the formulas to show the reactants and products for the following laboratory situations described below. Assume that solutions are aqueous unless otherwise indicated. You need not balance the equations. A. Aqueous potassium fluoride is electrolyzed. B. Aqueous nickel(II) nitrate is electrolyzed. C. Molten aluminum oxide is electrolyzed. D. Aqueous cesium bromide is electrolyzed. E. Aqueous chromium(III) iodide is electrolyzed. F. Aqueous magnesium sulfide is electrolyzed. G. Aqueous ammonium chloride is electrolyzed. H. Molten lithium fluoride is electrolyzed.
2. Consider the electrolysis of AgF(aq) in acidic solution. A. What are the half-reactions that occur at each electrode? B. What is the minimum external emf required to cause this process to occur under standard conditions?
Finally, we consider the stoichiometric relationship that exists between charge and product in an electrolytic cell. This relationship was first determined experimentally by Michael Faraday and is referred to as Faraday s law of electrolysis: The amount of substance produced at each electrode is directly proportional to the quantity of charge flowing through the cell. Recall that Faraday s constant F = 96,500 C/mol e - . We turn to classical physics in order to relate charge per unit time, known as current and measured in terms of the ampere (A). Therefore, we define 1 ampere as 1 coulomb flowing through a conductor in 1 second. That is: 1 A = 1C/s Current (Amperes) & time Quantity of Charge (Coulombs) Moles of electrons (Faraday) Moles of substance (oxid or red) Grams of substance