An investigator wishes to identify an unknown divalent metal ion M in solution
CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
An investigator wishes to identify an unknown divalent metal ion M2+ in solution. In the first trial, a constant current of 5.00 A is passed through the solution for exactly 20.0 min, causing the cathode mass to increase by 1.20 g.
Assume the Faraday constant is 96 485 C mol−1 of electrons.
Candidate metals include Mg, Ca, and Zn.
(a) Using the data from the first trial, calculate the molar mass of the metal.
(b) Select the most likely metal from the candidate list and justify your selection.
(c) A second trial is carried out at a current of 3.00 A. Calculate the time required to deposit an additional 0.60 g of the same metal onto the cathode.
(d) Briefly discuss the assumption made about the oxidation state of the metal ion in these calculations and explain how an incorrect assumption would affect your answers in parts (a) and (c).