Chapter 21, Problem 105A

(a)

Interpretation Introduction

Interpretation: The given reaction is a redox reaction needs to be identified. Also, the element oxidized and reduced needs to be identified.

  ${\text{CaCO}}_{\text{3}}\left(s\right)\to \text{CaO}\left(s\right)+{\text{CO}}_2\left(g\right)$

Concept Introduction: A reaction in which oxidation and reduction take place simultaneously is known as a redox reaction.

Explanation of Solution

The given reaction is as follows:

  ${\text{CaCO}}_{\text{3}}\left(s\right)\to \text{CaO}\left(s\right)+{\text{CO}}_2\left(g\right)$

Here, the oxidation state of Ca in ${\text{CaCO}}_{\text{3}}$ and $\text{CaO}$ is +2 thus, Ca does not undergo oxidation or reduction. The oxidation state of C in ${\text{CaCO}}_{\text{3}}$ and ${\text{CO}}_2$ can be calculated as follows:

  $\begin{array}{c}{\text{CO}}_{\text{3}}{}^{2-}\to x+3\left(-2\right)=-2\\ x-6=-2\\ x=-2+6\\ x=+4\end{array}$

  $\begin{array}{c}{\text{CO}}_2\to x+2\left(-2\right)=0\\ x-4=0\\ x=+4\end{array}$

Oxidation state of C is also the same it does not undergo oxidation or reduction.

Thus, the given reaction is not a redox reaction.

(b)

Interpretation Introduction

Interpretation: The given reaction is a redox reaction needs to be identified. Also, the element oxidized and reduced needs to be identified.

  $\text{Ca}\left(s\right)+{\text{Cl}}_{\text{2}}\left(g\right)\to {\text{CaCl}}_{\text{2}}\left(s\right)$

Concept Introduction: A reaction in which oxidation and reduction take place simultaneously is known as a redox reaction.

Explanation of Solution

The given reaction is as follows:

  $\text{Ca}\left(s\right)+{\text{Cl}}_{\text{2}}\left(g\right)\to {\text{CaCl}}_{\text{2}}\left(s\right)$

Here, the oxidation state of Ca in $\text{Ca}\left(s\right)$ is 0 and that in ${\text{CaCl}}_{\text{2}}\left(s\right)$ is +2. Thus, oxidation of Ca takes place.

Similarly, the oxidation state of ${\text{Cl}}_{\text{2}}\left(g\right)$ is 0 and that of ${\text{CaCl}}_{\text{2}}\left(s\right)$ is -1. Thus, a reduction of Cl takes place.

In the given reaction since both reduction and oxidation takes place, the reaction is a redox reaction.

Here, the element oxidized is Ca and the element reduced is Cl.

(c)

Interpretation Introduction

Interpretation: The given reaction is a redox reaction needs to be identified. Also, the element oxidized and reduced needs to be identified.

  $\text{Ca}\left(s\right)+{\text{2H}}_{\text{2}}\text{O}\left(l\right)\to \text{Ca}{\left(\text{OH}\right)}_{\text{2}}\left(aq\right)+{\mathrm{H}}_2\left(g\right)$

Concept Introduction: A reaction in which oxidation and reduction take place simultaneously is known as a redox reaction.

Explanation of Solution

The given reaction is as follows:

  $\text{Ca}\left(s\right)+{\text{2H}}_{\text{2}}\text{O}\left(l\right)\to \text{Ca}{\left(\text{OH}\right)}_{\text{2}}\left(aq\right)+{\mathrm{H}}_2\left(g\right)$

The oxidation state of Ca in $\text{Ca}\left(s\right)$ and $\text{Ca}{\left(\text{OH}\right)}_{\text{2}}\left(aq\right)$ is 0 and +2 respectively. Similarly, the oxidation state of H in ${\text{H}}_{\text{2}}\text{O}\left(l\right)$ and ${\mathrm{H}}_2\left(g\right)$ is +1 and 0 respectively.

Since both oxidation and reduction reactions take place, the above reaction is a redox reaction.

Here, the element oxidized is Ca and the element reduced is H.