Question

The standard reduction potentials at \(25^{\circ} \mathrm{C}\) of \(\mathrm{Li}^{+}\left|\mathrm{Li}, \mathrm{Ba}^{2+}\right| \mathrm{Ba}, \mathrm{Na}^{+} \mid \mathrm{Na}\) and \(\mathrm{Mg}^{2+} \mid \mathrm{Mg}\) are \(-3.05,-2.73,-2.71\) and \(-2.37 \mathrm{~V}\), respectively. Which is the strongest reducing agent? (a) \(\mathrm{Li}\) (b) \(\mathrm{Ba}\) (c) \(\mathrm{Na}\) (d) \(\mathrm{Mg}\)

Short answer

Lithium (Li) is the strongest reducing agent.

Step-by-step solution

Understanding Reduction Potentials

The reduction potential of an element is a measure of the tendency of a chemical species to gain electrons and thereby be reduced. A more negative reduction potential indicates a greater tendency to lose electrons and, as a result, act as a better reducing agent.

Comparing the Reduction Potentials

To determine the strongest reducing agent, compare the standard reduction potentials for the given elements. The element with the most negative potential is the strongest reducing agent since it has the greatest tendency to lose electrons.

Identifying the Strongest Reducing Agent

Here are the standard reduction potentials for the elements provided: Li: -3.05 VBa: -2.73 VNa: -2.71 VMg: -2.37 VSince lithium (Li) has the most negative reduction potential at -3.05 V, it is the strongest reducing agent among those listed.

Key concepts

Standard Reduction Potential

Understanding standard reduction potential (SRP) is key when studying electrochemistry, as it tells us about a substance's ability to gain electrons. SRP is measured in volts (V) and is determined under standard conditions, which is at a temperature of 25 degrees Celsius, a 1 Molar solution, and at 1 atmosphere of pressure for gasses.

Chemical species with a more negative SRP are considered better reducing agents because they have a higher tendency to lose electrons and be oxidized themselves. Think of SRP as a 'score' that indicates how eager a species is to snatch electrons – the more negative the score, the more eager it is. In the exercise, lithium (Li) had the most negative SRP at -3.05 V, marking it as the best reducing agent among the options provided.

Chemical Species

A chemical species might sound like a term borrowed from biology, but in chemistry, it refers to form of an element or compound in a particular state that has a unique reactivity. For example, an atom, ion, molecule, or a radical can all be considered chemical species. These species can undergo chemical reactions, including redox reactions, which involve the transfer of electrons.

In electrochemistry, the behavior of chemical species in terms their ability to either gain or lose electrons is critical. This behavior conditions not only their role in redox reactions but also informs us regarding their corrosiveness, electrical conductivity, and battery chemistry.

Electron Gain Tendency

The tendency of a chemical species to gain electrons is described as its electron gain tendency. This propensity plays a pivotal role in redox reactions, influencing how a species will interact with others. It is related to several factors, including atomic size, nuclear charge, and the overall energy change associated with the gain of an electron.

Species with high electron gain tendency often have a strong affinity for electrons and are likely to be good oxidizing agents. Conversely, species with low electron affinity tend to lose electrons easily, making them strong reducing agents. In our exercise, lithium's exceptional readiness to lose electrons is exactly what makes it the strongest reducing agent.

Redox Reactions

Redox reactions, short for reduction-oxidation reactions, are processes where electrons are transferred between chemical species. This tandem of processes is inseparable – as one species undergoes reduction (gains electrons), another must be oxidized (lose electrons).

The concept of reducing agents and oxidizing agents comes into play here, with reducing agents being the donors of electrons and oxidizing agents the acceptors. The strength of a reducing agent, as we've seen with lithium in the exercise, is intrinsically tied to its standard reduction potential. Redox reactions are fundamental to energy production, metallurgy, cellular respiration, and many applications in chemistry.