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MCAT Chemistry Question — Standard State Cell Potential
- by
- May 06, 2018
- MCAT Question of the Day
The standard reduction potentials for Zn and Cu are given below:
Zn2+(aq) + 2e– → Zn(s) E°= -0.76 V
Cu+(aq) + e– → Cu(s) E°= 0.52 V
What is the standard state cell potential for the following reaction?
Zn(s) + 2Cu+(aq) → Zn2+(aq) + 2Cu(s)
A. -1.8V
B. -1.28V
C. 0.28V
D. 1.28V
Click for Explanation
Given the standard reduction potentials:
Zn2+(aq) + 2e– → Zn(s) E°= -0.76 V
Cu+(aq) + e– → Cu(s) E°= 0.52 V
The reduction potentials are used as is or multiplied by -1 if the reaction direction is reversed. Stoichiometry does not matter, the reduction potentials are summed for the standard cell potential.
Zn(s) + 2Cu+(aq) → Zn2+(aq) + 2Cu(s)
0.76V + 0.52V=1.28V
- -1.8V, incorrect, This uses Zinc in the wrong direction (it should be +0.76V), and copper is also in the wrong direction and multiplied twice. There should be no multiplying for stoichiometric coefficients.
- -1.28V, incorrect, This uses Zinc in the wrong direction and copper in the wrong direction.
- 0.28V, incorrect, This uses Zinc in the right direction and Cu in the wrong direction.
- 1.28V, correct.
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