Oxides and Ozone

There are different types of oxides, which include the following:

(1). Basic oxides - these are metallic oxides which react with acids to form salts and water only.

Those that are soluble in water form alkaline solutions.

Example: CaO_(s) + 2HCl_(aq) → CaCl_2(aq) + H₂O_(l)

CaO_(s) + H₂O_(l) → Ca(OH)_2(aq) - alkali

Other basic oxides include Na₂O, K₂O, CuO and MgO

(2). Acidic oxides - these are non-metallic oxides which dissolve in water to form acids. They are also called acid anhydrides.

Examples include CO₂, SO₂, SO₃, and SiO₂

(3). Amphoteric oxides - these are metallic oxides which are insoluble in water, but will react with solutions of strong acids or bases to form either salts and water only or form complex salts only.

This behaviour is called amphoterism.

Examples include oxide of: zinc, lead, beryllium, iron, silver, gold, and Aluminium.

As a base:

ZnO_(s) + H₂SO_4(aq) → ZnSO_4(aq) + H₂O_(l)

Al₂O_3(s) + 6HCl_(aq) → 2AlCl_3(aq) + 3H₂O_(l)

As an acid:

ZnO_(s) + 2NaOH_(aq) + H₂O_(l) → Na₂Zn(OH)_4(aq) -- sodium tetrahydroxo zincate(II)

Al₂O_3(s) + 2NaOH_(aq) + 3H₂O_(l) → 2NaAl(OH)_4(aq) -- sodium tetrahydroxo aluminate(III)

Notice that the oxide of hydrogen, H₂O, is also classified as an amphoteric oxide because it contains both acidic and basic characters: H₂O → H⁺ + OH^-

(4). Neutral oxides - these are oxides which behave neither acidic nor basic.

Examples of such oxides include dinitrogen oxide, N₂O, carbon monoxide, CO and nitrogen monoxide, NO.

(5). Peroxides - these are oxides with greater proportion of oxygen than the ordinary oxides.

Examples are sodium peroxide, Na₂O₂, calcium peroxide, CaO₂ and Barium peroxide, BaO₂.

Note:

* The oxidation state of oxygen in peroxides is -1

* Peroxides produce hydrogen peroxide when treated with dilute acids.

Example, BaO_2(s) + H₂SO_4(aq) → BaSO_4(s) + H₂O_2(aq)

(6). Superoxides - these are produced when the heavier alkaline metals (potassium, rubidium and cesium) react with oxygen.

Here, the oxidation state of oxygen is - ¹/₂ . An example of superoxides is KO₂. They are coloured solids, and are paramagnetic because the superoxide ion, O₂^-, contains an unpaired electron. This ion exists only in the solid state.

In the presence of water, superoxides produce oxygen and hydrogen peroxide:

2KO_2(s) + 2H₂O_(l) → H₂O_2(aq) + 2K⁺_(aq) + 2OH^-_(aq) + O_2(g)

(7). Other Higher oxides - these also, like the peroxides contain a higher proportion of oxygen than the ordinary oxides, but they do not produce hydrogen peroxide with acids.

Note: these oxides are oxidizing agents, and when heat is applied on them, they liberate oxygen.

Example include: manganese(IV) oxide, MnO₂; lead(IV) oxide, PbO₂; dilead(II) lead(IV) oxide (red lead oxide), Pb₃O₄; and iron(II) diiron(III) oxide (or tri-iron tetraoxide), Fe₃O₄ .

Ozone, O₃ - Allotrope of Oxygen

Ozone, O₃ and oxygen are allotropes of the same element. An evidence of this is that there is no change in mass if one is converted to the other.

Ozone has a very important environmental consequence - it is found as a layer in the atmosphere. This layer, called ozone layer, protects the earth from exposures to harmful ultraviolet rays from the sun, by shielding the earth from these rays.