Problem 21 - Chemistry and Chemical Reactivity

Question

Which of the following ions is most easily reduced? (a) \(\mathrm{Cu}^{2+}(\mathrm{aq})\) (b) \(\mathrm{Zn}^{2+}(\mathrm{aq})\) (c) \(\mathrm{Fe}^{2+}(\mathrm{aq})\) (d) \(\mathrm{Ag}^{+}(\mathrm{aq})\) (e) \(\mathrm{Al}^{3+}(\mathrm{aq})\)

Step-by-Step Solution

Answer

(d) \( \mathrm{Ag}^{+} \) is most easily reduced, with a reduction potential of +0.80 V.

Step 1: Determine Reduction Potentials

The reduction potential of an ion is a measure of its tendency to gain electrons and be reduced. To determine which ion is most easily reduced, we must look at the standard reduction potentials (E°) for each ion listed in the exercise.

Step 2: List Standard Reduction Potentials

For each of the ions listed, find the standard reduction potential:- \( \mathrm{Cu}^{2+} + 2e^- \rightarrow \mathrm{Cu} \),\( E^\circ = +0.34 \text{ V} \)- \( \mathrm{Zn}^{2+} + 2e^- \rightarrow \mathrm{Zn} \),\( E^\circ = -0.76 \text{ V} \)- \( \mathrm{Fe}^{2+} + 2e^- \rightarrow \mathrm{Fe} \),\( E^\circ = -0.44 \text{ V} \)- \( \mathrm{Ag}^{+} + e^- \rightarrow \mathrm{Ag} \),\( E^\circ = +0.80 \text{ V} \)- \( \mathrm{Al}^{3+} + 3e^- \rightarrow \mathrm{Al} \),\( E^\circ = -1.66 \text{ V} \)

Step 3: Compare Reduction Potentials

Compare the standard reduction potentials. The species with the highest (most positive) reduction potential is the one that is most easily reduced.From the potentials listed, \( \mathrm{Ag}^{+} \) has the highest reduction potential of \( +0.80 \text{ V} \).

Step 4: Conclusion

Since \( \mathrm{Ag}^{+} \) has the highest standard reduction potential among the given ions, it is the most easily reduced compared to the other ions listed.

Key Concepts

Reduction potential

Reduction potential is a key concept in electrochemistry that indicates how likely a chemical species is to gain electrons, which is known as being reduced. It quantifies this tendency and is usually expressed in volts.

To visualize, consider an ion: if it gains electrons, it becomes reduced, and its reduction potential shows how readily this process occurs.
Positive reduction potentials signify that a species tends to gain electrons easily, while negative values suggest the opposite.

In our exercise, comparing the reduction potentials of various ions helps determine which ones get reduced most quickly.

• Higher reduction potentials mean a greater likelihood of being reduced.
• This indicates an eagerness to gain electrons.

If you ever have a list of different ions, just pick the one with the highest positive reduction potential for the easiest reduction.

Standard electrode potential

The standard electrode potential (abbreviated as E°) is a specific type of reduction potential. It informs us about the potential a half-cell has under standard conditions, such as a concentration of 1 M, pressure of 1 atm, and a temperature of 25°C (298 K).

The standard electrode potential enables comparisons because it's measured against a standard hydrogen electrode reference, chosen for its zero potential, so every other potential is compared to it.
For instance, let's look at silver ions, which have a standard reduction potential of +0.80 V.

• This positive E° shows that silver ions readily accept electrons.
• Being high, it surpasses many other ions in the ease of reduction.

When you're assessing multiple ions like in the exercise, check their E° values.
Whichever is more positive is more likely to gain electrons under standard conditions.

Ion reduction

Ion reduction refers to when ions gain electrons during chemical reactions, a process at the heart of many electrochemical and redox reactions. It’s pivotal in fields like batteries, galvanic cells, and metallurgy.

In the lab or in technology, reducing an ion means it gains electrons and switches to a simpler charge state or even becomes neutral.
Understanding which ions are easily reduced can help in selecting the right materials or reactions for specific applications.

• For example, in the exercise, silver ions (Ag⁺) tend to undergo reduction easily due to their high standard reduction potential.
• This property is particularly useful in reactions requiring efficient electron transfers.

Balancing ion reduction in reactions ensures that energy is effectively harnessed or released in processes like energy storage or corrosion prevention.