Question

Using the tables of standard electrode potentials, arrange the following substances in decreasing order of ability as reducing agents: \(\mathrm{Al}, \mathrm{Co}, \mathrm{Ni}, \mathrm{Ag}, \mathrm{H}_{2}, \mathrm{Na}\).

Short answer

The decreasing order of ability as reducing agents for the given substances is: \(\mathrm{Na}>\mathrm{Al}>\mathrm{Co}>\mathrm{Ni}>\mathrm{H}_{2}>\mathrm{Ag}\).

Step-by-step solution

Gather standard electrode potentials of each species

Consult the table of standard electrode potentials and note down the standard reduction potential values for each substance provided: - \(\mathrm{Al}^{3+} + 3e^- \rightarrow \mathrm{Al}\): \(E^°=-1.66V\) - \(\mathrm{Co}^{2+} + 2e^- \rightarrow \mathrm{Co}\): \(E^°=-0.28V\) - \(\mathrm{Ni}^{2+} + 2e^- \rightarrow \mathrm{Ni}\): \(E^°=-0.26V\) - \(\mathrm{Ag}^{+} + e^- \rightarrow \mathrm{Ag}\): \(E^°= 0.80V\) - \(\mathrm{H}^{+} + e^- \rightarrow \frac{1}{2}\mathrm{H}_{2}\): \(E^°=0.00V\) - \(\mathrm{Na}^{+} + e^- \rightarrow \mathrm{Na}\): \(E^°=-2.71V\)

Arrange in the order of decreasing reduction potentials

To find which substance is the strongest reducing agent, we will arrange the substances in the order of decreasing standard reduction potential values. \(\mathrm{Na}>{\mathrm{Al}>{\mathrm{Co}>{\mathrm{Ni}>{\mathrm{H}_{2}>{\mathrm{Ag}\)

Evaluate the result

The decreasing order of ability as reducing agents (from strongest to weakest) for the given substances is: \(\mathrm{Na}>\mathrm{Al}>\mathrm{Co}>\mathrm{Ni}>\mathrm{H}_{2}>\mathrm{Ag}\)

Key concepts

Standard Electrode Potentials

Understanding the concept of standard electrode potentials is crucial in predicting the behavior of different elements in electrochemical reactions. The standard electrode potential, often represented as \(E^\circ\), is a measure of the tendency of a chemical species to be reduced. It is measured in volts (V) and is defined under standard conditions: a temperature of 298 K, a 1 molar solution for each ion participating in the reaction, and a pressure of 1 atm for any gases involved.

The standard electrode potential is a relative measure, which we compare against the standard hydrogen electrode (SHE) set at \(0.00V\). If a substance has a positive standard electrode potential, it means it is more favorable to be reduced (gain electrons) relative to the SHE. If the potential is negative, the substance is less likely to be reduced than hydrogen ions. By comparing the potentials, chemists can predict the spontaneity of redox reactions and determine the strength of reducing and oxidizing agents.

For instance, as seen in the exercise, sodium (Na) with a standard reduction potential of \(-2.71V\) is a stronger reducing agent than aluminum (Al) with \(-1.66V\). This indicates that Na is more inclined to lose electrons and undergo oxidation.

Reduction Potential

The reduction potential, specifically the standard reduction potential discussed in the exercise, is an invaluable tool for determining the tendency of a species to accept electrons and undergo reduction. Reduction is one half of a redox process and involves the gain of electrons. When a chemical species has a higher reduction potential, it means it is more likely to gain electrons and be reduced. Conversely, a lower or more negative reduction potential suggests it will more readily donate electrons, acting as a reducing agent.

In the exercise, we observed that substances like \(\text{Ag}^+\) with a high positive standard reduction potential of \(0.80V\) are less likely to act as reducing agents. On the other hand, elements like \(\text{Na}^+\) and \(\text{Al}^{3+}\) with highly negative values demonstrate a greater tendency to give up electrons and serve as strong reducing agents.

Learning to arrange substances based on their reduction potential enables students to predict the direction of electron flow in electrochemical cells and understand the underlying principles governing redox reactions and electrode behaviors in different chemical systems.

Chemical Reduction

Chemical reduction involves the process of gaining electrons in a chemical reaction. It plays a fundamental role in redox (reduction-oxidation) reactions, where there is a transfer of electrons between species. One of the key points in chemical reduction is identifying the reducing agent: the substance that donates electrons to another substance. This is essentially the atom or molecule that gets oxidized in the process of reducing another.

In our exercise, we classified substances according to their ability to act as reducing agents, which is inversely proportional to their standard reduction potentials. A good reducing agent will have a low (or negative) reduction potential, reflecting its propensity to lose electrons. For example, sodium (Na) and aluminum (Al) are strong reducing agents because they readily undergo oxidation, giving away electrons to reduce other substances. This behavior is linked to their position in the electrochemical series and can be exploited in applications such as metal extraction or battery technology.

Grasping the concept of chemical reduction not only helps solve textbook problems but also provides insights into practical applications such as corrosion prevention, metabolic processes in biology, and synthetic chemistry where reduction reactions are fundamental.