AP Chemistry 9.11 A Calculate the Amount of Charge Flow Based on Changes in the Amounts of Reactants and Products in an Questions

Practice AP Chemistry questions on calculating charge flow, current, time, deposited mass, and electron transfer in electrochemical cells.

Exam points

Relate current, charge, and time using I = q/t in an electrochemical cell.
Use redox stoichiometry and Faraday’s constant to calculate electron flow from mass or ionic charge.
Calculate deposited electrode mass or electrolysis time from charge, current, and electron transfer.

[Maximum number: 2]

Sterling silver is an alloy that is commonly used to make jewelry and consists of 92.5\% silver and 7.5\% other metals, such as copper, by mass. Over time, the alloy can form a tarnish of $\mathrm{Ag}_{2} \mathrm{~S}(s)$ when it reacts with hydrogen sulfide, as represented by the following equation.

2 \mathrm{Ag}(s)+\mathrm{H}_{2} \mathrm{~S}(g) \rightarrow \mathrm{Ag}_{2} \mathrm{~S}(s)+\mathrm{H}_{2}(g)

Calculate the length of time, in seconds, required to plate 2.8 g of Rh(s) onto a piece of sterling silver if 2.0 C / s of current is applied.

For the correct calculated value of moles of electrons (may be implicit): 1 point

2.8 \mathrm{~g} \mathrm{Rh} \times \frac{1 \mathrm{~mol} \mathrm{Rh}}{102.9 \mathrm{~g} \mathrm{Rh}} \times \frac{3 \mathrm{~mol} e^{-}}{1 \mathrm{~mol} \mathrm{Rh}}=0.082 \mathrm{~mol} e^{-}

For the correct calculated value of time: 1 point

0.082 \mathrm{~mol} e^{-} \times \frac{96,485 \mathrm{C}}{1 \mathrm{~mol} e^{-}} \times \frac{1 \text { second }}{2.0 \mathrm{C}}=3900 \text { seconds }

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AP Chemistry 9.11 A Calculate the Amount of Charge Flow Based on Changes in the Amounts of Reactants and Products in an Questions question 1