Question

The decreasing order of standard electrode potential of \(\mathrm{Mg}, \mathrm{K}, \mathrm{Ba}\) and \(\mathrm{Ca}\), is (a) \(\mathrm{K}, \mathrm{Ca}, \mathrm{Ba}, \mathrm{Mg}\) (b) \(\mathrm{Ba}, \mathrm{Ca}, \mathrm{K}, \mathrm{Mg}\) (c) \(\mathrm{Ca}, \mathrm{Mg}, \mathrm{K}, \mathrm{Ba}\) (d) \(\mathrm{Mg}, \mathrm{Ca}, \mathrm{Ba}, \mathrm{K}\)

Short answer

The decreasing order of standard electrode potential of Mg, K, Ba, and Ca is (d) Mg, Ca, Ba, K.

Step-by-step solution

Understanding Standard Electrode Potentials

To solve this exercise, you need to understand that the standard electrode potential (SEP) of an element is a measure of its ability to be reduced, and it is represented by its standard reduction potential. A higher standard electrode potential means that the element is more likely to gain electrons and be reduced. Conversely, a lower standard electrode potential means the element is less likely to gain electrons and be reduced.

Consulting the Standard Electrode Potential Table

The next step is to consult a table of standard electrode potentials to find the values for the elements Mg, K, Ba, and Ca. These tables are found in textbooks or reputable scientific sources. For this exercise, the typical electrode potentials from the table (in volts) might look like this: Mg: -2.37VK: -2.93VBa: -2.90VCa: -2.87VIt is important to note that these values are negative because all these elements are less noble than hydrogen and have a tendency to lose electrons (oxidation), but the higher the value, the less negative it is, and the stronger the element is as a reducing agent.

Ranking the Elements by Standard Electrode Potential

To arrange the elements in decreasing order of standard electrode potential, we will list them from the least negative SEP value to the most negative SEP value. This will show us which element is more likely to be reduced (i.e., has a stronger tendency to gain electrons): 1. Mg: -2.37V (least negative, highest SEP)2. Ca: -2.87V3. Ba: -2.90V4. K: -2.93V (most negative, lowest SEP)This ranking is in decreasing order of standard electrode potential.

Key concepts

Chemical Reactivity

Understanding the chemical reactivity of metals is essential when dealing with compounds and reactions in chemistry. Chemical reactivity refers to the tendency of a substance to engage in chemical reactions, either by losing, gaining, or sharing electrons. In the case of metals, reactivity is often discussed in the context of their ability to lose electrons and form positive ions. This process is known as oxidation.

Metals like Mg, K, Ba, and Ca are considered to be highly reactive. They readily lose electrons when they come into contact with other substances. This is why they are usually found in nature as compounds rather than as pure elements. By using the standard electrode potentials, we can compare their reactivity quantitatively. The less negative the standard electrode potential, the higher is the tendency of the metal to gain electrons and therefore, the lower its reactivity in terms of oxidation. Mg, having the least negative standard electrode potential, is the least likely to lose electrons, thus it is the least reactive among the given metals in terms of oxidation.

Redox Reactions

Redox reactions are a type of chemical reaction that involves the transfer of electrons between two species. These reactions are a combination of two simultaneous processes: oxidation (loss of electrons) and reduction (gain of electrons). The element that loses electrons is oxidized, while the element that gains electrons is reduced.

Standard electrode potentials are integral in understanding redox reactions because they help us predict the direction of electron flow. In a redox reaction between two elements, the one with higher electrode potential will typically be reduced, while the other with a lower potential will be oxidized. Let's apply this to our metals: since magnesium has the least negative standard electrode potential among the four, it is less likely to be oxidized; thus, when reacting with any of the other three metals (K, Ba, or Ca), Mg is more likely to remain in its reduced state.

Electrochemical Series

The electrochemical series is a list of elements arranged in order of their standard electrode potentials. This series predicts how different metals will react relative to each other, particularly in terms of their tendency to lose or gain electrons. Metals that are higher in the series have higher standard reduction potentials and are less inclined to lose electrons (less reactive in terms of oxidation). Conversely, metals lower in the series have lower electrode potentials and are more inclined to lose electrons (more reactive).

When we consider the elements Mg, K, Ba, and Ca, we can arrange them according to their standard electrode potentials, as seen in the exercise. This ordering forms part of the electrochemical series, with magnesium at the top (least negative, least reactive) and potassium at the bottom (most negative, most reactive). Consequently, if we place these metals in an electrochemical cell, the metal higher in the series would act as the cathode (the electrode where reduction takes place) and the metal lower in the series would act as the anode (the electrode where oxidation occurs).