Question

Redox Reaction. Which of the following ions is reduced by copper metal? a. Ca+ / b. Fe+3 / c. Hg+2 / d. Mg+2

I don't understand the question. For me it seems that a lot of context was left out, so please explain which is the right answer.

Answer 1

You're right! This is a typical exam question in chemistry. You're expected to understand many details that are (indeed) missing.

The only way to get this question "right" is a thorough understanding (which comes through intense study), which is why not many students finish a typical chemistry series in college. Where I go, maybe 25-35% of the students who started finish (55-60% exam averages are normal). Now that this is out of the way,

Here, we would need data to determine this. Specifically, we would need reduction potentials of each of the cations, commonly found in a general (or physical) chemistry text. The one I used is one posted by Colorado State. I'll assume you can relate the values in the table to one's I'm using here.

Hence,

`Cu(s) to Cu^(2+)` is our source of electrons to reduce the cation, where `E° = 0.34`.

In order for a compound to reduced by copper, its reduction potential must be more than copper's.

According to the preceding data, `Hg^(2+)` is viable option to be reduced via that specific oxidation of copper I noted.