CHM 2354 Lecture Notes - Lecture 12: Faraday Constant, Oxidizing Agent, Galvanic Cell

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25 May 2015

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Redox reactions involve the transfer of electrons from one species to another the oxidative state of the chemical changes. We can monitor redox reactions when electrons flow through an electric current. The current is proportional to the rate of reduction. Cell voltage is proportional to free-energy change. Batteries produce a direct current by converting chemical energy to electrical energy. A substance is reduced when it gains electrons from another substance. Gain of e net decrease in charge of species. A substance is oxidized when is loses electrons to another substance. Loss of e net increase in charge of species. The first two reactions are known as 1/2 cell reactions and include electrons in their equations. The not reaction is known as the total cell reaction. In order for a redox reaction to occur, both reduction of one compound and oxidation of another must take place simultaneously the total number of electrons is constant.

Related Questions

Check your ability to correctly define some of the terms associated with redox reactions.

(a) A chemical species that gets reduced during a chemical reaction: loses electrons or gains electrons?

(b) A chemical species that gets reduced during a chemical reaction: changes to a more negative oxidation state or changes to a more positive oxidation state?

(d) A chemical species that gets reduced during a chemical reaction: has a high-energy filled orbital or has a low-energy unfilled orbital?

(e) A chemical species that gets reduced during a chemical reaction: obtains electrons from a reducing agent or obtains electrons from an oxidizing agent?

ambersardine273

Initial observations: before beginning Observations Observations after 30 minutes Chemical equation Element that is oxidized Element that is reduced Spectator ion Oxidizing agent Reducing agent www.HOLscience.com 16 Â©Hands-On Labs, Inc. Experiment Oxidation-Reduction Activity Series Questions A. Define oxidation, reduction, and oxidation number. Describe how oxidation and reduction affect the oxidation number of an element. B. Define oxidizing agent, reducing agent, and spectator ion. C. In the reaction of copper and silver nitrate, a new substance appeared in the test tube. Describe the physical appearance of the substance and identify its chemical formula. D. Given an activity series in which the most active metals are at the top of the list and the least active metals are at the bottom of the list, would copper be listed above silver or would silver be listed above copper? Support your answer with data from Data Table 1. E. Solid copper sulfide and silver nitrate react to form copper (II) nitrate and solid silver sulfide. Write a balanced chemical equation that describes the reaction. Identify the oxidation number of each element in the reaction. (You do not need to include the total contribution of charge.) Is this reaction a redox reaction or a non-redox reaction? Explain your answer. www.HOLscience.com 17 Â©Hands-On Labs, Inc. Experiment Oxidation-Reduction Activity Series Exercise 2: Creating an Activity Series Data Table 2. Redox Reactions of Copper, Lead, and Zinc Solid metal Well ID Solution Immediate observations 30 Minute Observations Cu A1 Pb(NO3 ) 2 A2 Zn(NO3 ) 2 Pb B1 CuSO4 B2 Zn(NO3 ) 2 Zn C1 CuSO4 C2 Pb(NO3 ) 2 Data Table 3. Potential Redox Reactions and Chemical Equations Metal and Metallic Solution Reaction Occurred? Chemical Equation Cu + Pb(NO3 ) 2 Cu + Zn(NO3 ) 2 Pb + CuSO4 Pb + Zn(NO3 ) 2 Zn + CuSO4 www.HOLscience.com 18 Â©Hands-On Labs, Inc. Experiment Oxidation-Reduction Activity Series Zn + Pb(NO3 ) 2 Questions A. List each of the metals tested in Exercise 2. Indicate the oxidation number when each element is pure and the oxidation number when each element is in a compound. B. Which of the metals in Exercise 2 was the strongest oxidizing agent? Was there an instance when this metal also acted as a reducing agent? Explain your answer using data from Data Table 3. C. Which of the metals in Exercise 2 was the strongest reducing agent? Was there an instance when this metal also acted as an oxidizing agent? Explain your answer using data from Data Table 3. D. How does ease of oxidation correlate with activity? Do highly active metals tend to donate electrons or accept electrons from other metals? E. Create an activity series for copper, lead, and zinc. Place the most active metal at the top of the list.

Having trouble with my Pre-Lab questions I don't understand how to get them.

Introduction An important type of reaction mechanism is the transfer of electrons from one species to another effecting a change in oxidation state. This gain or loss of electrons is referred to as reduction and oxidation, respectively. For example, consider the two balanced, chemical equations (1 & 2) that follow Cu (s) D Cu (aq) 2e (1) Cl2(aq) 2e D 2Cl (aq) (2) The first equation (1) shows elemental copper metal with a oxidation state of zero forming aqueous copper(Il) ions having an oxidation state of +2. This gain in oxidation number, 0 to +2, is called oxidation. The second equation (2) show elemental chlorine having an oxidation state of zero forming chloride ions in aqueous solution with an oxidation state of This decrease in oxidation number, 0 to -1, is called reduction. In any chemical reaction, the electrons gained or lost are conserved, i.e.. there is no net gain or loss of electrons. In fact, the two reactions illustrated above could occur simultaneously with the electrons lost by copper, gained by the chlorine in aqueous solution. Since the copper provides the electrons that subsequently reduce the chlorine copper is referred to as the reducing agent. Likewise, since the chlorine is accepting the electrons from copper, which subsequently oxidizes the copper, chlorine is referred to as he oxidizing agent. The two reactions above (1 & 2) are called half-reactions, as much as they each constitute one-half of the total reaction Equation 1 is the oxidation half reaction showing Cu(s) losing two electrons. In Equation 2, Cla(aq) gains two electrons and is the reduction half-reaction. If these two half-reaction are added together the result is the total oxidation-reduction reaction or "redox" reaction. Adding the two equations yields (3). Cu(s) Cl2(aq) D Cu (aq) 2CI (aq) (3) Whether or not the above reaction is spontaneous proceeds from reactants to products without input of energy into the system, may be determined by observing the reaction mixture if the reactants and products differ greatly in their appearance. Copper metal is a bright copper color and chlorine in aqueous solution will appear yellow. The Cu ion may turn the liquid part of the mixture blue, however, the Cris colorless and cannot be observed directly. Copper, like many of the transition metals, exhibits a variety of oxidation states depending upon the chemical environment in which it is found. In a strong reducing environment copper may exist as the free metal, Cu(s). An example of such a situation is illustrated in the following chemical equation (4). 4Cuo(s) CH4(g) D 4Cu(s) CO2(g) 2H2O(l) (4)

CHM 2354 Lecture Notes - Lecture 12: Faraday Constant, Oxidizing Agent, Galvanic Cell

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