A sample containing M ions (where M is an unknown metal) is electrolyzed in an…
CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
A sample containing M2+ ions (where M is an unknown metal) is electrolyzed in an aqueous cell that uses inert electrodes. A constant current of 2.80 A is maintained for 30.0 min. During the electrolysis the following observations are recorded:
• Mass of the cathode increases by 1.09 g as M plates out.
• Oxygen gas produced at the anode is collected over water; its volume is 115 mL at 25 °C and 1.00 atm.
Assume the Faraday constant is 96 485 C mol−1 of electrons and the ideal-gas constant is 0.08206 L atm mol−1 K−1.
Possible identities for M include Fe, Ni, and Zn.
(a) Calculate the number of moles of O2 gas collected and the corresponding number of moles of electrons consumed in producing that O2.
(b) Determine the number of moles of electrons that were instead used to deposit metal on the cathode.
(c) Using the data from part (b) and the measured mass gain of the cathode, calculate the molar mass of the metal.
(d) Identify the metal from the list provided and justify your choice with quantitative reasoning.