Chapter 19: Problem 74
Identify each of the following changes as either oxidation or reduction. a. \(2 {Cl}^{-} \rightarrow {Cl}_{2}+2 {e}^{-}\) c. \({Ca}^{-2}+2 {e}^{-} \rightarrow 2 {Ca}\) b. \({Na} \rightarrow {Na}^{+}+{e}^{-}\) {d} . \({O}_{2}+4 \mathrm{e}^{-} \rightarrow 2 {O}^{2-}\)
Short Answer
Expert verified
a. Oxidation
b. Oxidation
c. Reduction
d. Reduction
Step by step solution
01
Identify electron transfer in reaction a.
We will look at the first reaction: \(2 Cl^- \rightarrow Cl_2 + 2 e^-\). In this reaction, two chloride ions (each with a charge of -1) lose one electron each, forming a neutral chlorine molecule and two electrons: \[2 Cl^- \rightarrow Cl_2 + 2 e^-\]
02
Classify reaction a as oxidation or reduction.
Since in reaction a, we see that the chloride ions are losing electrons, this is an example of oxidation.
03
Identify electron transfer in reaction b.
We will now look at the second reaction: \(Na \rightarrow Na^+ + e^-\). In this reaction, a neutral sodium atom loses one electron to form a sodium ion with a charge of +1: \[Na \rightarrow Na^+ + e^-\]
04
Classify reaction b as oxidation or reduction.
Since in reaction b, we see that the sodium atom is losing an electron, this is another example of oxidation.
05
Identify electron transfer in reaction c.
Next, we examine the third reaction: \(Ca^{2+} + 2 e^- \rightarrow Ca\). In this reaction, a calcium ion with a charge of +2 gains two electrons, forming a neutral calcium atom: \[Ca^{2+} + 2 e^- \rightarrow Ca\]
06
Classify reaction c as oxidation or reduction.
Since in reaction c, we see that the calcium ion is gaining electrons, this is an example of reduction.
07
Identify electron transfer in reaction d.
Finally, we look at the fourth reaction: \(O_2 + 4 e^- \rightarrow 2 O^{2-}\). In this reaction, one oxygen molecule gains four electrons, forming two oxide ions (each with a charge of -2): \[O_2 + 4 e^- \rightarrow 2 O^{2-}\]
08
Classify reaction d as oxidation or reduction.
Since in reaction d, we see that the oxygen molecule is gaining electrons, this is another example of reduction.
So to sum up, the reactions can be classified as follows:
a. Oxidation
b. Oxidation
c. Reduction
d. Reduction
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Oxidation and Reduction
Understanding the nature of oxidation and reduction is essential for diving into the complex world of chemical reactions. These are two halves of a type of chemical process known as redox reactions, which are fundamental to many forms of life and a myriad of industrial processes.
Oxidation involves the loss of electrons from an element. When we say an atom is oxidized, it means it's given up one or more electrons. This may seem counterintuitive, because the element's charge becomes more positive, but remember: electrons are negatively charged, so losing them increases the positive charge of the atom. In our textbook exercise, when we see chloride ions (\( 2Cl^- \rightarrow Cl_2 + 2e^- \) and sodium atoms (\( Na \rightarrow Na^+ + e^- \) ) losing electrons, these are clear examples of oxidation.
Conversely, reduction is the gain of electrons. When a substance is reduced, it adds electrons to its structure, which decreases its oxidation state—reducing the positive charge or increasing the negative charge of the molecule or atom. Reduction can be easy to spot when you see an atom or ion gaining electrons, such as the calcium ion (\( Ca^{2+} + 2 e^- \rightarrow Ca \) ) and oxygen molecule (\( O_2 + 4 e^- \rightarrow 2 O^{2-} \) ) in the exercise. The central mantra to remember for these processes is 'LEO the lion says GER': Lose Electrons Oxidation, Gain Electrons Reduction.
Oxidation involves the loss of electrons from an element. When we say an atom is oxidized, it means it's given up one or more electrons. This may seem counterintuitive, because the element's charge becomes more positive, but remember: electrons are negatively charged, so losing them increases the positive charge of the atom. In our textbook exercise, when we see chloride ions (\( 2Cl^- \rightarrow Cl_2 + 2e^- \) and sodium atoms (\( Na \rightarrow Na^+ + e^- \) ) losing electrons, these are clear examples of oxidation.
Conversely, reduction is the gain of electrons. When a substance is reduced, it adds electrons to its structure, which decreases its oxidation state—reducing the positive charge or increasing the negative charge of the molecule or atom. Reduction can be easy to spot when you see an atom or ion gaining electrons, such as the calcium ion (\( Ca^{2+} + 2 e^- \rightarrow Ca \) ) and oxygen molecule (\( O_2 + 4 e^- \rightarrow 2 O^{2-} \) ) in the exercise. The central mantra to remember for these processes is 'LEO the lion says GER': Lose Electrons Oxidation, Gain Electrons Reduction.
Electron Transfer
The very essence of redox reactions is the transfer of electrons. This exchange is not just a simple shift; it's a fundamental change that affects the entire structure and energy of the reacting substances. Understanding electron transfer helps us decipher why and how chemical reactions occur.
Electrons are the currency of chemical reactions. When an atom or ion loses or gains an electron, its properties change. This is why the reactions we see in the exercise are significant. An element's ability to donate or accept electrons can determine the types of chemical bonds it forms, its reactivity, and even its role in biological systems. For example, in our reaction b (\( Na \rightarrow Na^+ + e^- \)), sodium is more reactive and willing to part with its electron, which is characteristic of metals, particularly those in Group 1 of the periodic table.
In reaction c, the reverse is occurring. The calcium ion is eager to return to a more stable state by gaining electrons (\( Ca^{2+} + 2 e^- \rightarrow Ca \)). This electron transfer is what drives the process of reduction and is also reflected in reaction d with oxygen (\( O_2 + 4 e^- \rightarrow 2 O^{2-} \) ).
Electrons are the currency of chemical reactions. When an atom or ion loses or gains an electron, its properties change. This is why the reactions we see in the exercise are significant. An element's ability to donate or accept electrons can determine the types of chemical bonds it forms, its reactivity, and even its role in biological systems. For example, in our reaction b (\( Na \rightarrow Na^+ + e^- \)), sodium is more reactive and willing to part with its electron, which is characteristic of metals, particularly those in Group 1 of the periodic table.
In reaction c, the reverse is occurring. The calcium ion is eager to return to a more stable state by gaining electrons (\( Ca^{2+} + 2 e^- \rightarrow Ca \)). This electron transfer is what drives the process of reduction and is also reflected in reaction d with oxygen (\( O_2 + 4 e^- \rightarrow 2 O^{2-} \) ).
Chemical Changes
During redox reactions, substances undergo chemical changes that alter their identity and properties. These changes can be observed and measured in a variety of ways.
For instance, when a metal oxidizes, it might change color, produce heat, or become less reactive. Think of rust forming on iron: this is oxidation at work in the real world. Similarly, when nonmetallic substances like oxygen or chlorine gain electrons, they usually change from a gaseous state to become part of a compound, often altering their color or odor.
In our exercise solutions, each reaction signifies a profound chemical change. For example, the oxidation of chloride ions results in the formation of chlorine gas (\( 2Cl^- \rightarrow Cl_2 + 2 e^- \)), a change from individual ions to a diatomic molecule. On the reduction side, calcium ions accepting electrons (\( Ca^{2+} + 2 e^- \rightarrow Ca \) ) turn into solid metal calcium, highlighting the transformative power of electron transfer in chemical reactions.
For instance, when a metal oxidizes, it might change color, produce heat, or become less reactive. Think of rust forming on iron: this is oxidation at work in the real world. Similarly, when nonmetallic substances like oxygen or chlorine gain electrons, they usually change from a gaseous state to become part of a compound, often altering their color or odor.
In our exercise solutions, each reaction signifies a profound chemical change. For example, the oxidation of chloride ions results in the formation of chlorine gas (\( 2Cl^- \rightarrow Cl_2 + 2 e^- \)), a change from individual ions to a diatomic molecule. On the reduction side, calcium ions accepting electrons (\( Ca^{2+} + 2 e^- \rightarrow Ca \) ) turn into solid metal calcium, highlighting the transformative power of electron transfer in chemical reactions.