Question

The oxidation potential of \(\mathrm{Mg}\) and \(\mathrm{Al}\) are \(+2.37\) and \(+1.66\) volts respectively. The \(\mathrm{Mg}\) in the chemical reaction (a) will be replaced by Al (b) will replace \(\mathrm{Al}\) (c) will not be able to replace \(\mathrm{Al}\) (d) none of the above

Short answer

Therefore the correct answer is (b): \(\mathrm{Mg}\) will replace \(\mathrm{Al}\).

Step-by-step solution

Identify the oxidation potentials

The problem states that the oxidation potential of \(\mathrm{Mg}\) is \(+2.37\) volts and of \(\mathrm{Al}\) is \(+1.66\) volts. This means \(\mathrm{Mg}\) has a higher tendency to lose electrons or get oxidized compared to \(\mathrm{Al}\).

Predict the replacement

In replacement reactions, an element with a higher oxidation potential will tend to replace an element with a lower oxidation potential, because the element with the higher oxidation potential has a stronger tendency to lose electrons. Based on the given oxidation potentials, \(\mathrm{Mg}\) with a higher oxidation potential, can replace \(\mathrm{Al}\), which has a lower oxidation potential.

Key concepts

Electrochemical Series

Understanding electrochemical series is essential when predicting the outcomes of chemical reactions, particularly redox and replacement reactions. The series arranges elements by their standard electrode potentials, which represent their ability to gain or lose electrons. A more positive potential indicates a greater tendency to get oxidized and lose electrons. Therefore, elements with higher oxidation potentials act as stronger oxidizing agents.

In the context of the exercise, magnesium (Mg) has an oxidation potential of +2.37 volts, while aluminum (Al) has an oxidation potential of +1.66 volts. This implies that Mg is more readily oxidized than Al. In practice, this means that if Mg and Al were both in solution and a suitable electrode were introduced to facilitate electron flow, Mg would lose electrons (be oxidized) before Al.

When comparing elements in the electrochemical series, remember that those higher up will tend to be replaced by the elements lower down in a replacement reaction due to their higher oxidation potential.

Redox Reactions

Redox reactions are a family of reactions that involve the transfer of electrons between substances. These reactions are shorthand for 'reduction-oxidation' reactions, signifying that one substance is reduced (gains electrons) and another is oxidized (loses electrons).

In redox reactions, the substance with the higher oxidation potential, like Mg in our exercise, is more likely to be oxidized. This means it will lose electrons and form a positive ion. The other material, such as Al, with a lower oxidation potential, is more likely to gain those electrons in turn, thus being reduced. Understanding which substance gets oxidized and which gets reduced is fundamental in predicting the course of a redox reaction.

Chemical Reactivity

Chemical reactivity refers to the propensity of a substance to engage in a chemical reaction. The reactivity of an element is influenced by its position in the electrochemical series. Generally, the further apart two elements are in this series, the more vigorously they will react with each other.

In relation to the exercise, because Mg has a higher oxidation potential than Al, it is considered more reactive in terms of its tendency to form compounds by losing electrons. Mg's high reactivity means that it can displace less reactive metals from their compounds in a replacement reaction. The higher the oxidation potential, the greater the chemical reactivity of the element.

Replacement Reactions

Replacement reactions, also known as single displacement or substitution reactions, occur when an element in a compound is replaced by a more reactive element. To determine which element will replace another, we refer to the electrochemical series, which gives us a hierarchy of element reactivity. An element higher up in the series can replace an element lower down.

Applying this to our initial problem: Mg has a higher oxidation potential than Al and is therefore more reactive. According to the principles governing replacement reactions, Mg will replace Al in a chemical reaction because it has a stronger tendency to lose electrons and react. This helps us conclude that answer (b) will replace Al is the right choice.