CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
In an instructional electroplating experiment, a research-grade instrument counts the total number of electrons that pass through the circuit during the deposition of copper metal onto a cathode. The instrument registers 5.20×1021 electrons, and the mass of copper deposited is measured as 0.523g. Copper metal forms by reduction of Cu2+ ions according to the half-reaction
Cu2+(aq)+2e−⟶Cu(s).
Use the data to answer the questions below.
(a) Calculate the amount, in moles, of electrons that passed through the circuit.
(b) Using the stoichiometry of the half-reaction, determine the theoretical amount, in moles, of copper metal that could be deposited by the measured electron count.
(c) From the measured mass of copper and its molar mass of 63.55gmol−1, calculate the experimental amount of copper actually deposited, in moles. Then compute the percent discrepancy between this experimental amount and the theoretical amount from part (b).
(d) Using the ratio of the measured electron count to the experimental amount of copper calculated in part (c), estimate a value for Avogadro’s number. Compare your estimate qualitatively with the accepted value and discuss two plausible sources of experimental error that could account for any difference.