Question

Refer to standard reduction potentials, and predict which metal in each of the following pairs is the stronger reducing agent: (a) sodium or potassium (b) magnesium or barium

Short answer

The stronger reducing agent in the first pair (sodium and potassium) is potassium. In the second pair (magnesium and barium), barium is the stronger reducing agent.

Step-by-step solution

Determine the Standard Reduction Potentials

Refer to a standard reduction potentials table. The standard reduction potential of sodium is -2.71V and for potassium is -2.93V (values are approximate and may vary slightly depending on the source used). For magnesium it is -2.37V and for barium it is -2.92V.

Compare the Reduction Potentials for Sodium and Potassium

Compare the standard reduction potentials of sodium and potassium. Potassium has a more negative reduction potential (-2.93V) than sodium (-2.71V).

Identify the Stronger Reducing Agent in the First Pair

The metal with the more negative reduction potential will be the stronger reducing agent. In the case of sodium and potassium, that is potassium.

Compare the Reduction Potentials for Magnesium and Barium

Now, compare the standard reduction potentials of magnesium and barium. Barium has a more negative reduction potential (-2.92V) than magnesium (-2.37V).

Identify the Stronger Reducing Agent in the Second Pair

In the case of magnesium and barium, barium is the stronger reducing agent because it has a more negative standard reduction potential than magnesium does.

Key concepts

Reducing Agent Strength

When comparing the reducing ability of different metals, we look to their standard reduction potentials, also referred to as redox potentials. These potentials are measured under standard conditions, typically at a concentration of 1M for each ion, a pressure of 1atm for gases, and a temperature of 25°C (298 K).

In simple terms, the standard reduction potential indicates the tendency of a substance to gain electrons and thus be reduced. A more negative reduction potential suggests a greater tendency to donate electrons to other substances, acting as a reducing agent.

For example, in comparing sodium (-2.71V) and potassium (-2.93V), we can determine that potassium, with its more negative reduction potential, is the stronger reducing agent. This implies that potassium is more likely to give up its electrons during a chemical reaction, making it more effective at reducing other substances.

Electrochemical Series

The electrochemical series, also known as the activity series, is a powerful tool in predicting the outcome of redox reactions. It ranks elements according to their standard reduction potentials. The series places the most powerful reducing agents, which have the most negative reduction potentials, at the top, and the weakest, which have the least negative (or most positive) potentials, at the bottom.

The position of an element within this series helps predict how it will behave in combination with other substances. For instance, because potassium appears higher up in the series compared to sodium due to its more negative potential (-2.93V vs -2.71V), it serves as a stronger reducing agent.

Understanding the Electrochemical Series:

• Metals towards the top of the series readily lose electrons and have a strong tendency to form positive ions.
• Halogens, and certain other non-metals that are positioned towards the bottom of the series, have a tendency to gain electrons and form negative ions.
• The series can also offer insights into the spontaneity of redox reactions between two substances.

Chemical Reactivity of Metals

The chemical reactivity of metals is intimately linked with their standard reduction potentials. Highly reactive metals, such as those found in the alkali and alkaline earth metals groups, have more negative standard reduction potentials.

These metals, including potassium and barium which have potentials of -2.93V and -2.92V respectively, are so reactive because they have a strong desire to lose electrons and form positive ions. This makes them excellent reducing agents in redox reactions.

Implications of Metal Reactivity:

• HIGHLY REACTIVE METALS: These metals can displace hydrogen from water and are quickly oxidized in air.
• LESS REACTIVE METALS: These metals, such as copper or silver, are less likely to oxidize and are often found in nature in their native, or uncombined, states.

The understanding of metal reactivity can also dictate its extraction method, storage conditions, and safety measures during handling. For example, potassium, being highly reactive, must be stored in oil to prevent it from reacting with moisture or oxygen in the air.