Question

From each of the following pairs of substances, use data in Appendix \(\mathrm{E}\) to choose the one that is the stronger reducing agent: (a) \(\mathrm{Fe}(s)\) or \(\mathrm{Mg}(s)\) (b) \(\mathrm{Ca}(s)\) or \(\mathrm{Al}(s)\) (c) \(\mathrm{H}_{2}(g\), acidic solution \()\) or \(\mathrm{H}_{2} \mathrm{~S}(g)\) (d) \(\mathrm{H}_{2} \mathrm{SO}_{3}(a q)\) or \(\mathrm{H}_{2} \mathrm{C}_{2} \mathrm{O}_{4}(a q)\)

Short answer

The stronger reducing agents are: (a) Mg(s), (b) Ca(s), (c) H₂S(g), and (d) H₂C₂O₄(aq).

Step-by-step solution

Analyze Data from Appendix E

First, gather the standard reduction potentials for each substance from Appendix E. Keep in mind that a lower reduction potential indicates a stronger reducing agent. (a) For Fe and Mg, \(E°_{Fe^{2+}/Fe(s)} = -0.44 V\) and \(E°_{Mg^{2+}/Mg(s)} = -2.37 V\) (b) For Ca and Al, \(E°_{Ca^{2+}/Ca(s)} = -2.87 V\) and \(E°_{Al^{3+}/Al(s)} = -1.66 V\) (c) For H₂ (in acidic solution) and H₂S, \(E°_{2H^{+}/H_2(g)} = 0.00 V\) and \(E°_{H^{+}/H_2S(g)}=-0.14 V\) (d) For H₂SO₃ and H₂C₂O₄, \(E°_{HSO_3^-/H_2SO_3(aq)}=0.60 V\) and \(E°_{C_2O_4^{2-}/H_2C_2O_4(aq)}=0.49 V\)

Compare Reduction Potentials

Compare the standard reduction potential values for each pair of substances. (a) For Fe and Mg, since \(E°_{Mg^{2+}/Mg(s)} < E°_{Fe^{2+}/Fe(s)}\), Mg(s) is the stronger reducing agent. (b) For Ca and Al, since \(E°_{Ca^{2+}/Ca(s)} < E°_{Al^{3+}/Al(s)}\), Ca(s) is the stronger reducing agent. (c) For H₂ (in acidic solution) and H₂S, since \(E°_{H^{+}/H_2S(g)} < E°_{2H^{+}/H_2(g)}\), H₂S(g) is the stronger reducing agent. (d) For H₂SO₃ and H₂C₂O₄, since \(E°_{C_2O_4^{2-}/H_2C_2O_4(aq)} < E°_{HSO_3^-/H_2SO_3(aq)}\), H₂C₂O₄(aq) is the stronger reducing agent.

Provide Final Answers

Based on the comparisons, we can conclude that the stronger reducing agent in each pair is: (a) Mg(s) (b) Ca(s) (c) H₂S(g) (d) H₂C₂O₄(aq)

Key concepts

Reduction Potential

Reduction potential is a crucial concept in electrochemistry. It measures a substance's tendency to gain electrons and be reduced. In a chemical reaction, substances with higher reduction potentials are more likely to be reduced, while those with lower reduction potentials act as stronger reducing agents.

Reduction potentials are often measured in volts (V) and the standard potential values are tabulated for reference. The sign and magnitude of a reduction potential can tell us a lot about the chemical activity of a substance. For example, a negative reduction potential indicates that a substance prefers to donate electrons rather than receive them, making it more likely to be oxidized.

Therefore, when comparing two substances, the one with the more negative reduction potential is considered a stronger reducing agent. This concept is key to understanding how reduction and oxidation work together in electrochemical reactions.

Electrochemistry

Electrochemistry is the study of chemical processes that cause electrons to move. This movement of electrons is usually related to electricity generation or storage. At the heart of electrochemistry are oxidation-reduction reactions, often called redox reactions.

In an electrochemical cell, these reactions occur at two different electrodes. One serves as the anode, where oxidation occurs, and the other as the cathode, where reduction takes place. The difference in electrochemical potential between these electrodes generates an electric current.

Within electrochemistry, understanding terms like electrolyte, anode, cathode, and electrode potential is important. Electrolytes are substances that conduct electricity when dissolved in water, while electrodes are the materials that serve as the site of oxidation or reduction. Electrochemical studies help in the development of batteries, corrosion prevention, and even electroplating, showcasing its wide applications.

Oxidation-Reduction Reactions

Oxidation-reduction reactions, or redox reactions, involve the transfer of electrons between substances. One substance loses electrons (oxidation) while another gains electrons (reduction). These reactions are vital to many processes, both biological and industrial.

To identify these reactions, look for changes in the oxidation state of the elements involved. The substance that is oxidized undergoes an increase in oxidation state, while the substance that is reduced shows a decrease.

Redox reactions often involve reducing agents and oxidizing agents. A reducing agent donates electrons and is oxidized in the process. Conversely, an oxidizing agent gains electrons and gets reduced. With this understanding, comparing reduction potentials of other substances becomes valuable, as we can determine which ones will act as reducing or oxidizing agents in chemical equations.

These basic principles of redox reactions provide a framework for understanding more complex chemical behaviors, including the energy changes and equilibrium scenarios involved in chemical cells and reactions.