A student electrolyzes of (aq) using inert platinum electrodes

CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry

Problem

A student electrolyzes

250\,\text{mL}

0.30\,\text{M}

\mathrm{Na_2SO_4}

(aq) using inert platinum electrodes. The only redox processes that occur are 2

\mathrm{H_2O}

(l) + 2

\mathrm{e^{-}}

→

\mathrm{H_2}

(g) + 2

\mathrm{OH^{-}}

(aq) (cathode) 2

\mathrm{H_2O}

(l) →

\mathrm{O_2}

(g) + 4

\mathrm{H^{+}}

(aq) + 4

\mathrm{e^{-}}

(anode) A

1.50\,\text{A}

constant current is supplied. After some time, the student collects

35.0\,\text{mL}

\mathrm{O_2}

gas measured at

25\,^{\circ}\text{C}

and

1.00\,\text{atm}

. Assume ideal-gas behavior, negligible vapor pressure of water, and that no other reactions occur. (a) Calculate the number of moles of

\mathrm{O_2}

produced, using the ideal gas law. (b) Determine the number of moles of electrons transferred at the anode to generate the amount of

\mathrm{O_2}

calculated in part (a). (c) Calculate the total electrical charge that passed through the cell during this time period. (d) Using the current supplied, compute the duration of the electrolysis in minutes. (e) If the student’s stopwatch indicated that the electrolysis actually ran for

22.0\,\text{min}

, calculate the current efficiency of the experiment and propose a plausible explanation for any discrepancy between the theoretical and experimental efficiency.

Related theory

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