Magnesium redox reactions

Let s examine some of these redox reactions and look for their common characteristic. First, consider the reaction between magnesium and oxygen, which produces magnesium oxide (Fig. K.l) this reaction is used in fireworks to produce white sparks. It is also used, less agreeably, in tracer ammunition and incendiary devices. The reaction of magnesium and oxygen is a classic example of an... 

Redox reactions are more complicated than precipitation or proton transfer reactions because the electrons transferred in redox chemishy do not appear in the balanced chemical equation. Instead, they are hidden among the starting materials and products. However, we can keep track of electrons by writing two half-reactions that describe the oxidation and the reduction separately. A half-reaction is a balanced chemical equation that includes electrons and describes either the oxidation or reduction but not both. Thus, a half-reaction describes half of a redox reaction. Here are the half-reactions for the redox reaction of magnesium and hydronium ions ... 

Separating oxidation from reduction makes it possible to verify that electrons are conserved in a redox reaction. Note that the electrons produced in the oxidation of magnesium are consumed in the reduction of hydronium ions. The electrons required for a reduction must come from an oxidation. 

Redox reactions of metals with acids are described in Chapter 4. Oxidation of the metal generates hydrogen gas and an aqueous solution of ions. Suppose that 3.50 g of magnesium metal is dropped into 0.150 L of 6.00 M HCl in a 5.00-L cylinder at 25.0 °C whose initial gas pressure is 1.00 atm, and the cylinder is immediately sealed. Find the final partial pressure of hydrogen, the total pressure in the container, and the concentrations of all ions in solution. 

A simple example of a redox reaction Is the violent reaction of magnesium metal with molecular oxygen to generate magnesium oxide, shown in Figure 19-1 2 Mg( ) + 02(g) 2 MgO(5 ) In magnesium metal, each atom is... 

Magnesium cations and oxide anions attract each other strongly, forming the ionic solid, MgO. Notice that in the balanced redox reaction there is no net change in the number of electrons two Mg atoms lose four electrons, and one O2 molecule gains four electrons. 

The description of redox reactions may afresh be carried out by introducing oxidation and reduction as an electron-transfer process. For this purpose, a process involving burning of magnesium in oxygen is considered, the reaction being written chemically as ... 

We know the reaction is complete when no more grey metal remains and the solution is clear. In fact, we often say the magnesium dissolves, although such dissolution is in fact a redox reaction (see Chapter 7). 

We may use the activity series to predict certain types of redox reactions. For example, suppose you wanted to write the equation between magnesium metal and hydrochloric acid ... 

You could balance the chemical equation for the reaction of magnesium with aluminum nitrate by inspection, instead of writing half-reactions. However, many redox equations are difficult to balance by the inspection method. In general, you can balance the net ionic equation for a redox reaction by a process known as the half-reaction method. The preceding example of the reaction of magnesium with aluminum nitrate illustrates this method. Specific steps for following the half-reaction method are given below. 

As seen from the change in valency of metal and hydrogen, this is a redox reaction because the metal is oxidized (loses n electrons) by the hydrogen, while the valence of hydrogen becomes, formally, -1. Magnesium dihydride, MgH, can be manufactured in ball mills in such a manner, with the reaction yield close to 90%. The reaction of... 

The reaction of magnesium and oxygen is an example of an oxidation reaction. The combination of an element with oxygen was the traditional way to define an oxidation reaction. This definition of oxidation has been broadened by chemists to include reactions that do not involve oxygen. Our modern definition for oxidation is that oxidation takes place when a substance loses electrons. Anytime oxidation takes place and a substance loses one or more electrons, another substance must gain the electron(s). When a substance gains one or more electrons, the process is known as reduction. Reactions that involve the transfer of one or more electrons always involve both oxidation and reduction. These reactions are known as oxidation-reduction or redox reactions. 

Using the Limiting Reagents (Stoichiometry) simulation (eChapter 3.6), perform the redox reaction between magnesium metal and oxygen gas by combining equal masses of both reactants. 

However, given the presence of these complexing agents in oxygen bleaching, what is required to prevent catalyzed oxidation is a stronger, stable complex that will not permit participation of the transition metals in the radical-redox reactions. This appears to be the most plausible role to ascribe to magnesium. 

When determining which substances were oxidized and reduced in a redox reaction, first assign the oxidation numbers to all the elements in the reaction. The formation for magnesium chloride serves as an example ... 

The reaction of magnesium and oxygen involves a transfer of electrons from magnesium to oxygen. Therefore, this reaction is an oxidation-reduction reaction. Using the classifications given in Chapter 10, this redox reaction also is classified as a combustion reaction. 

The same overall redox reaction occurs if the magnesium metal is placed directly into a solution of copper sulfate, Figure 17.12. However, this is not a galvanic cell because the electrons do not flow through an external circuit. Instead, the electrons move directly from the magnesium metal to the copper ions, forming copper metal. This is a way to make copper metal from copper ions, but it is not a way to make electrical power. 

Write the equation for the redox reaction that occurs when magnesium metal reacts with nitric acid. Name the oxidizing agent and the reducing agent. 

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