AP Chemistry Unit 9.10: Nonstandard Cell Potential

Practice AP Chemistry Unit 9.10 questions on predicting how concentration and reaction quotient changes affect cell potential near equilibrium.

[Maximum number: 2]

Metal-air cells are a relatively new type of portable energy source consisting of a metal anode, an alkaline electrolyte paste that contains water, and a porous cathode membrane that lets in oxygen from the air. A schematic of the cell is shown above. Reduction potentials for the cathode and three possible metal anodes are given in the table below.

Table for Question 9.10 Cell Potential Under Nonstandard Conditions question 1 — AP Chemistry

(a)

The zinc-air cell is taken to the top of a mountain where the air pressure is lower.

[ 2 ]

(i)

Will the cell potential be higher, lower, or the same as the cell potential at the lower elevation?

[ 1 ]

(ii)

Justify your answer to part (c)(i) based on the equation for the overall cell reaction and the information above.

[ 1 ]

(\mathrm{O}_{2}(g)\), a reactant in the cell reaction, will be at a
lower partial pressure at the higher elevation; thus
the reaction has a greater value of Q (closer to K ).
Deviations in partial pressure that take the cell
closer to equilibrium will decrease the magnitude
of the cell potential.

1 point is earned for a justification that relates a
lower pressure (or concentration) of $\mathrm{O}_{2}(g)$ to Q,
or a qualitative approach using the Nernst
equation.

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Covered syllabus points

9.10 Cell Potential Under Nonstandard Conditions question 1

Question (a)

Question (i)

Question (ii)