Title: Lesson 4 Period 3 Oxides

Learning Objectives:

• Understand and explain the trend in acid-base behaviour of the period 3 oxides

• Complete an experiment to demonstrate the amphoteric nature of aluminium oxide

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Which properties of the alkali metals decrease going down group 1?

A. First ionization energy and reactivityB. Melting point and atomic radiusC. Reactivity and electronegativityD. First ionization energy and melting point

The Period 3 OxidesElement Formula of

oxideStructure Reaction of oxide with water Acid/base

natureSodium* Na2O Giant Ionic Na2O + H2O 2NaOH Strongly basic

Magnesium* MgO Giant Ionic Slight: MgO + H2O Mg(OH)2Weakly basic

Aluminium Al2O3 Giant Ionic Amphoteric

Silicon SiO2 Giant Covalent (Metalloid)

Very weakly acidic

Phosphorous* P4O10 Molecular Covalent P4O10 + 6 H2O 4 H3PO4Strongly acidic

Sulphur* SO2SO3

Molecular CovalentSO3 + H2O H2SO4

Strongly acidic

Chlorine no direct reaction but:Cl2O7

Molecular Covalent

Cl2O7 + H2O 2 HClO4

Strongly acidic

Argon no oxides

There is a gradual transition from basic to acidic character, reflecting a gradual transition from metallic to non-metallic nature

Note: you will only be tested on the elements marked with an asterisk, *

13.3 OXIDES WITH ACIDS & BASESpH OF PERIOD 3 OXIDES:

Na2OMgO

Al2O3SiO2

P4O10SO2SO3

13.3 OXIDES WITH ACIDS & BASESA CLASSIC

The equation for neutralising an acid with a base is a classic

Acid + Base Salt + Water

It’s no different for Period 3 oxides

You will be expected to write the equations

SODIUM & MAGNESIUM:

Na2(s) + H2O(l) 2NaOH (aq) (Alkaline solution formed)

These oxides are basic so will neutralise acids.

E.g. Sodium oxide reacts with hydrochloric acid to form Sodium chloride and water

Na2O(s) + 2HCl(aq) 2NaCl(aq) + H2O(l)

E.g. Magnesium oxide reacts with sulphuric acid to form magnesium sulphate and water

MgO(s) + H2SO4(aq) MgSO4(aq) + H2O(l)

BASIC OXIDESCreate 2 other equations for Na & Mg with different acids

ALUMINIUM OXIDE:Aluminium Oxide does not affect pH when added to water because it is insoluble.This is an amphoteric oxide it can react with both acids and alkalisE.g. With sulphuric acid, aluminium sulphate is formed

Al2O3(s) + 3H2SO4(aq) Al2(SO4)3 (aq) + 3H2O(l)

Reaction with bases: Aluminum oxide also displays acidic properties, as shown in its reactions with bases such as sodium hydroxide. Various aluminates (compounds in which the aluminum is a component in a negative ion) exist, which is possible because aluminum can form covalent bonds with oxygen. E.g. With hot, concentrated sodium hydroxide, sodium aluminate is formed

Al2O3(s) + 2NaOH(aq) + 3H2O(l) 2NaAl(OH)4(aq)

AMPHOTERIC OXIDES

Acidic OxidesNon metallic oxides react with water to produce acidicsolutions:• Phosphorous(V) oxide reacts with water to produce:

• Phosphorous (III) oxide reacts with water to produce:

• Sulphur trioxide reacts with water to produce sulphuric(VI) acid:

• Sulphur dioxide reacts with water to produce sulphuric(IV) acid:

SILICON, PHOSPHOROUS & SULPHUR:

These oxides are all acidic so will neutralise bases

P4O10(s) + 12NaOH(aq) 4Na3PO4(aq) + 6H2O(l)

SO2(g) + 2NaOH(aq) Na2SO3(aq) + H2O(l)

SO3(g) + 2NaOH(aq) Na2SO4(aq) + H2O(l)

ACIDIC OXIDES