Ch.20 - Electrochemistry

Brown - Chemistry: The Central Science 14th Edition

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Brown 14th Edition

Ch.20 - Electrochemistry

Problem 12a

Chapter 20, Problem 12a

Magnesium, the element, is produced commercially by electrolysis from a molten salt (the 'electrolyte') using a cell similar to the one shown here. (a) What is the most common oxidation number for Mg when it is part of a salt?

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Identify the position of magnesium (Mg) in the periodic table. It is located in Group 2, which is also known as the alkaline earth metals.

Recall that elements in Group 2 typically form ions with a +2 charge because they have two valence electrons that they tend to lose in chemical reactions.

Understand that the oxidation number of an element in a compound is the charge it would have if all bonds were ionic. For magnesium, losing two electrons results in a +2 charge.

Conclude that the most common oxidation number for magnesium when it is part of a salt is +2.

Consider examples of magnesium salts, such as magnesium chloride (MgCl₂) or magnesium oxide (MgO), where magnesium exhibits a +2 oxidation state.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Oxidation Number

The oxidation number, or oxidation state, is a measure of the degree of oxidation of an atom in a compound. It indicates the number of electrons that an atom can gain, lose, or share when forming chemical bonds. For magnesium (Mg), the most common oxidation number is +2, which reflects its tendency to lose two electrons to achieve a stable electron configuration.

Ionic Compounds

Ionic compounds are formed when atoms transfer electrons, resulting in the formation of positively and negatively charged ions. In the case of magnesium salts, magnesium typically forms Mg²⁺ ions, which combine with anions (negatively charged ions) to create stable ionic compounds. Understanding the formation of these compounds is essential for predicting the behavior of magnesium in various chemical contexts.

Electrolysis

Electrolysis is a chemical process that uses electrical energy to drive a non-spontaneous reaction, often used to decompose compounds into their elements. In the context of magnesium production, electrolysis of molten magnesium salts allows for the extraction of magnesium metal by reducing Mg²⁺ ions to elemental magnesium. This process highlights the importance of oxidation states in understanding how elements behave during chemical reactions.

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The Electrolytic Cell

Related Practice

Textbook Question

Magnesium, the element, is produced commercially by electrolysis from a molten salt (the 'electrolyte') using a cell similar to the one shown here. (b) Chlorine gas is evolved as voltage is applied in the cell. Knowing this, identify the electrolyte.

The electrodes in a silver oxide battery are silver oxide 1Ag2O2 and zinc (b) Which battery do you think has an energy density most similar to the silver oxide battery: a Li-ion battery, a nickel– cadmium battery, or a lead–acid battery? [Section 20.7]

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Textbook Question

Magnesium, the element, is produced commercially by electrolysis from a molten salt (the 'electrolyte') using a cell similar to the one shown here. (c) Recall that in an electrolytic cell the anode is given the + sign and the cathode is given the – sign, which is the opposite of what we see in batteries. What half-reaction occurs at the anode in this electrolytic cell?

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