Oxide-Main group elements

Oxides are chemical compounds with one or more oxygen atoms combined with another element (e.g. Li₂O). Oxides are binary compounds of oxygen with another element, e.g., CO₂, SO₂, CaO, CO, ZnO, BaO₂, H₂O, etc. These are termed as oxides because here, oxygen is in combination with only one element. Based on their acid-base characteristics oxides are classified as acidic, basic, amphoteric or neutral:

1. An oxide that combines with water to give an acid is termed as an acidic oxide.
2. The oxide that gives a base in water is known as a basic oxide.
3. An amphoteric solution is a substance that can chemically react as either acid or base.
4. However, it is also possible for an oxide to be neither acidic nor basic, but is a neutral oxide.

Defferent type of oxides;-

Acidic Oxides

Acidic oxides are the oxides of non-metals (Groups 14-17) and these acid anhydrides form acids with water:

• Sulfurous Acid

SO2+H2O→H2SO3(1.1)$$\begin{array}{}\text{(1.1)}& {\text{SO}}_2^{}+{\text{H}}_2^{}\text{O}\to {\text{H}}_2^{}{\text{SO}}_3^{}\end{array}$$

• Sulfuric Acid

SO3+H2O→H2SO4(1.2)$$\begin{array}{}\text{(1.2)}& {\text{SO}}_3^{}+{\text{H}}_2^{}\text{O}\to {\text{H}}_2^{}{\text{SO}}_4^{}\end{array}$$

• Carbonic Acid

CO2+H2O→H2CO3(1.3)$$\begin{array}{}\text{(1.3)}& {\text{CO}}_2^{}+{\text{H}}_2^{}\text{O}\to {\text{H}}_2^{}{\text{CO}}_3^{}\end{array}$$

Acidic oxides are known as acid anhydrides (e.g., sulfur dioxide is sulfurous anhydride and sulfur trioxide is sulfuric anhydride) and when combined with bases, they produce salts, e.g.,

SO2+2NaOH→Na2SO3+H2O(1.4)$$\begin{array}{}\text{(1.4)}& {\text{SO}}_2^{}+2\text{NaOH}\to {\text{Na}}_2^{}{\text{SO}}_3^{}+{\text{H}}_2^{}\text{O}\end{array}$$

Basic Oxides

Generally Group 1 and Group 2 elements form bases called base anhydrides or basic oxides e.g.,

K2O(s)+H2O(l)→2KOH(aq)(1.5)$$\begin{array}{}\text{(1.5)}& {\text{K}}_2^{}\text{O}(\text{s})+{\text{H}}_2^{}\text{O}(\text{l})\to 2\text{KOH}(\text{aq})\end{array}$$

Basic oxides are the oxides of metals. If soluble in water, they react with water to produce hydroxides (alkalies) e.g.,

CaO+H2O→Ca(OH)2(1.6)$$\begin{array}{}\text{(1.6)}& \text{CaO}+{\text{H}}_2^{}\text{O}\to \text{Ca}{(\text{OH})}_2^{}\end{array}$$

MgO+H2O→Mg(OH)2(1.7)$$\begin{array}{}\text{(1.7)}& \text{MgO}+{\text{H}}_2^{}\text{O}\to \text{Mg}{(\text{OH})}_2^{}\end{array}$$

Na2O+H2O→2NaOH(1.8)$$\begin{array}{}\text{(1.8)}& {\text{Na}}_2^{}\text{O}+{\text{H}}_2^{}\text{O}\to 2\text{NaOH}\end{array}$$

These metallic oxides are known as basic anhydrides. They react with acids to produce salts, e.g.,

MgO+2HCl→MgCl2+H2O(1.9)$$\begin{array}{}\text{(1.9)}& \text{MgO}+2\text{HCl}\to {\text{MgCl}}_2^{}+{\text{H}}_2^{}\text{O}\end{array}$$

Na2O+H2SO4→Na2SO4+H2O(1.10)$$\begin{array}{}\text{(1.10)}& {\text{Na}}_2^{}\text{O}+{\text{H}}_2^{}{\text{SO}}_4^{}\to {\text{Na}}_2^{}{\text{SO}}_4^{}+{\text{H}}_2^{}\text{O}\end{array}$$

Amphoteric Oxides

An amphoteric solution is a substance that can chemically react as either acid or base. For example, when HSO₄^- reacts with water it will make both hydroxide and hydronium ions:

HSO−4+H2O→SO2−4+H3O+(1.11)$$\begin{array}{}\text{(1.11)}& HS{O}_4^{-}+H_{2}O\to S{O}_4^{2^{-}}+H_3{O}^{+}\end{array}$$

HSO−4+H2O→H2SO4+OH−(1.12)$$\begin{array}{}\text{(1.12)}& HS{O}_4^{-}+H_{2}O\to H_{2}S{O}_4+O{H}^{-}\end{array}$$

Amphoteric oxides exhibit both basic as well as acidic properties. When they react with an acid, they produce salt and water, showing basic properties. While reacting with alkalies they form salt and water showing acidic properties.

• For example ZnO$ZnO$ exhibits basic behavior with HCl$HCl$

ZnO+2HCl→ZnCl2zincchloride+H2O(basicnature)(1.13)$$\begin{array}{}\text{(1.13)}& ZnO+2HCl\to \underset{zincchloride}{ZnC{l}_2}+H_{2}O(basicnature)\end{array}$$

• and acidic behavior with NaOH$NaOH$

ZnO+2NaOH→Na2ZnO2sodiumzincate+H2O(acidicnature)(1.14)$$\begin{array}{}\text{(1.14)}& ZnO+2NaOH\to \underset{sodiumzincate}{N{a}_{2}Zn{O}_2}+H_{2}O(acidicnature)\end{array}$$

• Similarly, Al2O3$A{l}_2{O}_3$  exhibits basic behavior with H2SO4$H_{2}S{O}_4$

Al2O3+3H2SO4→Al2(SO4)3+3H2O(basicnature)(1.15)$$\begin{array}{}\text{(1.15)}& A{l}_2{O}_3+3H_{2}S{O}_4\to A{l}_2(S{O}_4{)}_3+3H_{2}O(basicnature)\end{array}$$

• and acidic behavior with NaOH$NaOH$

Al2O3+2NaOH→2NaAlO2+H2O(acidicnature)(1.16)$$\begin{array}{}\text{(1.16)}& A{l}_2{O}_3+2NaOH\to 2NaAl{O}_2+H_{2}O(acidicnature)\end{array}$$

Neutral Oxides

Neutral oxides show neither basic nor acidic properties and hence do not form salts when reacted with acids or bases, e.g., carbon monoxide (CO); nitrous oxide (N₂O); nitric oxide (NO), etc., are neutral oxides.

Peroxides and Dioxides

Oxides: Group 1 metals react rapidly with oxygen to produce several different ionic oxides, usually in the form of M2O$M_{2}O$ . With the oyxgen exhibiting an oxidation number of -2.

4Li+O2→2Li2O(1.17)$$\begin{array}{}\text{(1.17)}& 4Li+O_2\to 2L{i}_{2}O\end{array}$$

Peroxides: Often Lithium and Sodium reacts with excess oxygen to produce the peroxide, M2O2$M_2{O}_2$ . with the oxidation number of the oxygen equal to -1.

H2+O2→H2O2(1.18)$$\begin{array}{}\text{(1.18)}& H_2+O_2\to H_2{O}_2\end{array}$$

Superoxides: Often Potassium, Rubidium, and Cesium react with excess oxygen to produce the superoxide, MO2$M{O}_2$ . with the oxidation number of the oxygen equal to -1/2.

Cs+O2→CsO2(1.19)$$\begin{array}{}\text{(1.19)}& Cs+O_2\to Cs{O}_2\end{array}$$

A peroxide is a metallic oxide which gives hydrogen peroxide by the action of dilute acids. They contain more oxygen than the corresponding basic oxide, e.g., sodium, calcium and barium peroxides.

BaO2+H2SO4→BaSO4+H2O2(1.20)$$\begin{array}{}\text{(1.20)}& Ba{O}_2+H_{2}S{O}_4\to BaS{O}_4+H_2{O}_2\end{array}$$

Na2O2+H2SO4→Na2SO4+H2O2(1.21)$$\begin{array}{}\text{(1.21)}& N{a}_2{O}_2+H_{2}S{O}_4\to N{a}_{2}S{O}_4+H_2{O}_2\end{array}$$

Dioxides like PbO₂ and MnO₂ also contain higher percentage of oxygen like peroxides and have similar molecular formulae. These oxides, however, do not give hydrogen peroxide by action with dilute acids. Dioxides on reaction with concentrated HCl yield Cl₂ and on reacting with concentrated H₂SO₄ yield O₂.

PbO2+4HCl→PbCl2+Cl2+2H2O(1.22)$$\begin{array}{}\text{(1.22)}& Pb{O}_2+4HCl\to PbC{l}_2+C{l}_2+2H_{2}O\end{array}$$

2PbO2+2H2SO4→2PbSO4+2H2O+O2(1.23)$$\begin{array}{}\text{(1.23)}& 2Pb{O}_2+2H_{2}S{O}_4\to 2PbS{O}_4+2H_{2}O+O_2\end{array}$$

Compound Oxides

Compound oxides are metallic oxides that behave as if they are made up of two oxides, one that has a lower oxidation and one with a higher oxidation of the same metal, e.g.,

Red lead: Pb3O4=PbO2+2PbO(1.24)$$\begin{array}{}\text{(1.24)}& \text{Red lead: }P{b}_3{O}_4=Pb{O}_2+2PbO\end{array}$$

Ferro-ferric oxide: Fe3O4=Fe2O3+FeO(1.25)$$\begin{array}{}\text{(1.25)}& \text{Ferro-ferric oxide: }F{e}_3{O}_4=F{e}_2{O}_3+FeO\end{array}$$

On treatment with an acid, compound oxides give a mixture of salts.

Fe3O4Ferro-ferric oxide+8HCl→2FeCl3ferric chloride+FeCl2ferrous chloride+4H2O(1.26)