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Ch.20 - Electrochemistry
All textbooksBrown 14th EditionCh.20 - ElectrochemistryProblem 107
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Chapter 20, Problem 107

(a) How many coulombs are required to plate a layer of chromium metal 0.25 mm thick on an auto bumper with a total area of 0.32 m² from a solution containing CrO₄²⁻? The density of chromium metal is 7.20 g/cm³. (b) What current flow is required for this electroplating if the bumper is to be plated in 10.0 s? (c) If the external source has an emf of +6.0 V and the electrolytic cell is 65% efficient, how much electrical power is expended to electroplate the bumper?

Verified step by step guidance
1
Calculate the volume of chromium needed by multiplying the thickness (converted to meters) by the area of the bumper.
Use the density of chromium to convert the volume of chromium to mass.
Convert the mass of chromium to moles using the molar mass of chromium.
Determine the number of moles of electrons required using the stoichiometry of the reduction reaction: \( \text{CrO}_4^{2-} + 8e^- + 8H^+ \rightarrow \text{Cr} + 4\text{H}_2\text{O} \).
Calculate the total charge in coulombs using the number of moles of electrons and Faraday's constant (96,485 C/mol).
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Textbook Question

The capacity of batteries such as the typical AA alkaline battery is expressed in units of milliamp-hours (mAh). An AA alkaline battery yields a nominal capacity of 2850 mAh. (b) The starting voltage of a fresh alkaline battery is 1.55 V. The voltage decreases during discharge and is 0.80 V when the battery has delivered its rated capacity. If we assume that the voltage declines linearly as current is withdrawn, estimate the total maximum electrical work the battery could perform during discharge.

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Textbook Question

Disulfides are compounds that have S ¬ S bonds, like peroxides have O ¬ O bonds. Thiols are organic compounds that have the general formula R ¬ SH, where R is a generic hydrocarbon. The SH- ion is the sulfur counterpart of hydroxide, OH-. Two thiols can react to make a disulfide, R ¬ S ¬ S ¬ R. (b) What is the oxidation state of sulfur in a disulfide?

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Textbook Question

Disulfides are compounds that have S ¬ S bonds, like peroxides have O ¬ O bonds. Thiols are organic compounds that have the general formula R ¬ SH, where R is a generic hydrocarbon. The SH- ion is the sulfur counterpart of hydroxide, OH-. Two thiols can react to make a disulfide, R ¬ S ¬ S ¬ R. (c) If you react two thiols to make a disulfide, are you oxidizing or reducing the thiols?

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Open Question
Magnesium is obtained by electrolysis of molten MgCl2. (b) Several cells are connected in parallel by very large copper bars that convey current to the cells. Assuming that the cells are 96% efficient in producing the desired products in electrolysis, what mass of Mg is formed by passing a current of 97,000 A for a period of 24 h?
Textbook Question

Calculate the number of kilowatt-hours of electricity required to produce 1.0 * 103 kg (1 metric ton) of aluminum by electrolysis of Al3+ if the applied voltage is 4.50 V and the process is 45% efficient.

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Textbook Question

The Haber process is the principal industrial route for converting nitrogen into ammonia: N2(g) + 3 H2(g) → 2 NH3(g) (b) Using the thermodynamic data in Appendix C, calculate the equilibrium constant for the process at room temperature.

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