MCAT General Chemistry Question 239: Answer and Explanation
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Question: 239
1. Typical dry cell batteries contain a zinc anode and a carbon cathode and produce a potential difference of 1.5 V. Given that many electronic devices require additional voltage, which of the following would result in an overall increase in voltage?
I. Doubling the quantity of Zn(s)
II. Placing two batteries in parallel
III. Replacing Zn(s) with Na(s)
- A. I only
- B. III only
- C. I and II only
- D. II and III only
Correct Answer: B
Explanation:
B Increasing reagent quantity has no effect on voltage (Item I is incorrect, eliminating choices A and C), and placing batteries in parallel would leave the voltage unchanged (Item II is incorrect, eliminating choice D). Oxidation of zinc takes place at the anode, and sodium is a better reducing agent than zinc due to its lower ionization energy and tendency to give up an electron (Item III would result in an increase in voltage; the correct answer is choice B).