Chapter 21, Problem 1PS

Give examples of two basic oxides. Write equations illustrating the formation of each oxide from its component elements. Write another chemical equation that illustrates the basic character of each oxide.

Interpretation Introduction

Interpretation: Examples for two basic oxides has to be given. Equations illustrating the formation of each oxide from its component elements should be written.

Concept introduction: Oxides are formed by reaction of metal with oxygen. If metal belongs to group $\text{2A}$ of periodic table, then the general reaction of formation of oxide is:

    $\text{M}\left(\text{s}\right){\text{+O}}_{\text{2}}\left(\text{g}\right)\to \text{MO}\left(\text{s}\right)$

Here, metal has $+2$ oxidation number and oxide ion has $-2$ oxidation number.

A basic oxide is an oxide that shows basic properties in solution. Basic oxides on reaction with water form a base. This is a characteristic property of basic oxides and thus illustrates its basic behavior. Basic oxides are mostly oxides of group $\text{1A}$ and $\text{2A}$ elements. Thus, basic oxides are generally oxides of metals and they react with water to form alkaline solutions of metal hydroxides. The general reaction of a metal oxide with water is as follows:

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

Answer to Problem 1PS

The two example of basic oxides are $CaO$ and $MgO$.

The equation illustrating the formation of each oxide from its elements is:

For $\text{CaO}$,

    $2Ca\left(s\right)+O_2\left(g\right)\to 2CaO\left(s\right)$

For $\text{MgO}$,

    $2Mg\left(s\right)+O_2\left(g\right)\to 2MgO\left(s\right)$

The equation that illustrates the basic character of each oxide is:

For $\text{CaO}$,

    $CaO\left(s\right)+H_{2}O\left(l\right)\to Ca{\left(OH\right)}_2\left(aq\right)$

For $\text{MgO}$,

    $MgO\left(s\right)+H_{2}O\left(l\right)\to Mg{\left(OH\right)}_2\left(aq\right)$

Explanation of Solution

Basic oxides are generally oxides of metals of group $\text{1A}$ and $\text{2A}$ metals. The two examples of basic oxide are $\text{CaO}$ and $\text{MgO}$. Both calcium and magnesium belongs to group $\text{2A}$ of periodic table and have  highest oxidation number of $+2$. Oxide ion has oxidation number of $-2$. Thus, the formula of the product is $\text{CaO}$ and $\text{MgO}$ respectively.

Thus, the balanced chemical equation is:

• $\text{2Ca}\left(\text{s}\right){\text{+O}}_{\text{2}}\left(\text{g}\right)\to 2\text{CaO}\left(\text{s}\right)$
• $\text{2Mg}\left(\text{s}\right){\text{+O}}_{\text{2}}\left(\text{g}\right)\to 2\text{MgO}\left(\text{s}\right)$

The stoichiometric coefficients are multiplied with the compounds in the chemical equation to have equal number of atoms on both sides of the equation. Since oxygen is present as ${\text{O}}_{\text{2}}$ in the reaction, hence the stoichiometric coefficient of metal oxide is $2$ due to which metal also has a stoichiometric coefficient of $2$.

A major property of basic oxide that illustrates its basic character is that the basic oxides on reaction with water produce alkaline solution of hydroxides. Thus, the equation illustrating the basic character of each oxide is the reaction of its oxide with water.

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

Thus, both $\text{CaO}$ and $\text{MgO}$ forms alkaline solution of their hydroxides on reaction with water, which illustrates that these oxides are basic in nature.