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Ch.20 - Electrochemistry
Chapter 20, Problem 73b

During a period of discharge of a lead–acid battery, 402 g of Pb from the anode is converted into PbSO4(s). (b) How many coulombs of electrical charge are transferred from Pb to PbO2?

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Identify the chemical reaction occurring in the lead-acid battery during discharge. The anode reaction is: \[ \text{Pb} + \text{SO}_4^{2-} \rightarrow \text{PbSO}_4 + 2e^- \].
Determine the moles of Pb involved in the reaction. Use the molar mass of Pb (207.2 g/mol) to convert the given mass of Pb (402 g) to moles: \[ \text{moles of Pb} = \frac{402 \text{ g}}{207.2 \text{ g/mol}} \].
Calculate the total number of moles of electrons transferred. Since each mole of Pb produces 2 moles of electrons, multiply the moles of Pb by 2.
Use Faraday's constant to convert moles of electrons to coulombs. Faraday's constant is approximately 96485 C/mol. Multiply the moles of electrons by Faraday's constant to find the total charge in coulombs.
Summarize the process: The total charge transferred is the product of the moles of electrons and Faraday's constant, which gives the number of coulombs of electrical charge transferred from Pb to PbO2.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electrochemistry

Electrochemistry is the branch of chemistry that deals with the relationship between electrical energy and chemical reactions. In the context of batteries, it involves the transfer of electrons during redox reactions, where oxidation and reduction occur simultaneously. Understanding electrochemical processes is essential for analyzing how batteries function and how charge is transferred.
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Molar Mass and Stoichiometry

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole. Stoichiometry involves the calculation of reactants and products in chemical reactions based on balanced equations. In this question, knowing the molar mass of lead (Pb) allows for the conversion of mass to moles, which is crucial for determining the amount of charge transferred during the battery's discharge.
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Faraday's Law of Electrolysis

Faraday's Law states that the amount of substance transformed during electrolysis is directly proportional to the quantity of electric charge passed through the system. This principle allows for the calculation of the total charge (in coulombs) based on the number of moles of electrons involved in the reaction. In the case of the lead-acid battery, it helps determine how much charge is transferred when lead is converted to lead sulfate.
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