An electrolysis experiment is carried out on an acidic aqueous solution of…
CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
An electrolysis experiment is carried out on an acidic aqueous solution of cobalt(III) chloride, CoCl₃(aq), using inert platinum electrodes. A constant current of 1.60 A is passed for 25.0 min. During the run, two products form at the cathode: metallic cobalt and bubbles of hydrogen gas. After electrolysis has ended, the mass of cobalt deposited on the cathode is found to be 0.410 g, and 15.0 mL of H₂(g) is collected over water at 25 °C and 1.00 atm.
(The molar mass of Co is 58.9 g mol⁻¹. Water-vapor pressure at 25 °C is negligible compared with 1 atm.)
(a) Calculate the total number of moles of electrons that passed through the cell during electrolysis.
(b) Determine the number of moles of H₂(g) generated at the cathode. Show all work, including the use of the ideal-gas law.
(c) Using your answer from part (b), calculate the number of moles of electrons consumed in the production of the hydrogen gas.
(d) Subtracting the electrons accounted for in part (c) from the total electrons in part (a), determine the number of moles of electrons involved in the reduction of Co³⁺ to Co(s).
(e) From the data in part (d) and the measured mass of cobalt, calculate the integer number of electrons required to reduce one cobalt ion in this experiment. State that integer and comment on whether it is consistent with the initial oxidation state of cobalt in CoCl₃(aq).