International A LevelChemistryOxford AQARevision NotesInorganic ChemistryProperties of Period 3 Elements & Their OxidesReactions of the Period 3 Oxides & Chlorides

Reactions of the Period 3 Oxides & Chlorides (Oxford AQA International A Level Chemistry)

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Reactions of the Period 3 Oxides & Chlorides

  • You need to know the reactions of the following Period 3 oxides with water

Reaction of Period 3 oxides with water

Oxide

Chemical equation

pH

Na2O

Na2O (s) + H2O (l) → 2NaOH (aq)

14
(strongly alkaline)

MgO

MgO (s) + H2O (l) → Mg(OH)2 (aq) 

10
(weakly alkaline)

Al2O3

No reaction

-

SiO2

No reaction

-

P4O10

P4O10 (s) + H2O (l) → 4H3PO4 (aq)

2
(strongly acidic)

SO2

SO2 (g) + H2O (l) → H2SO3 (aq)

1
(strongly acidic)

SO3

SO3 (g) + H2O (l) → H2SO4 (aq)

1
(strongly acidic)

Acid / Base Nature of Period 3 Oxides

  • Aluminium oxide is amphoteric which means that it can act both as a base (and react with an acid such as HCl) and an acid (and react with a base such as NaOH)

Acidic and basic nature of Period 3 oxides table

Period 3 oxide

Na2O

MgO

Al2O3

SiO2

P4O10

SO2
SO3

Acid / base nature

Basic

Basic

Amphoteric

Acidic

Acidic

Acidic

Reaction of Period 3 oxides with acid / base table

Oxide

Chemical equation

Comment

Na2O

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

 

MgO

MgO (s) + 2HCl (aq) → MgCl2 (aq) + H2O (l)

Used in indigestion remedies by neutralising excess acid in the stomach

Al2O3

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

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

Reacts with acid to form salt and water


Reacts with hot, concentrated alkali to form salt

SiO2

SiO2 (s) + 2NaOH (aq)  → Na2SiO3 (aq) + H2O (l)

 

P4O10

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

SO2 

SO3

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

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

Reaction of Period 3 chlorides

Sodium & magnesium chloride

  • NaCl and MgCl2 do not react with water as the polar water molecules are attracted to the ions, dissolving the chlorides and breaking down the giant ionic structures: the metal and chloride ions become hydrated ions

The Periodic Table - Hydration of Sodium Chloride, downloadable AS & A Level Chemistry revision notes
The diagram shows water molecules breaking down the giant ionic structure of NaCl to form hydrated ions

Aluminium chloride

  • Aluminium chloride exists in two forms:

    • AlCl3 as a giant lattice and with ionic bonds

    • Al2Cl6 as a dimer with covalent bonds

AlCl3 and Al2Cl6

2-1-the-periodic-table---aluminium-chloride-new
The two forms in which aluminium chloride exists

  • When water is added to aluminium chloride the dimers are broken down and Al3+ and Cl- ions enter the solution

  • The highly charged Al3+ ion becomes hydrated and cause a water molecule that is bonded to the Al3+ to lose an H+ ion which turns the solution acidic

  • The H+ and the Cl- form hydrogen chloride gas which is given off as white fumes

How the Al3+ makes an acidic solution

Al3+ ion as an acid
The hydrated aluminium causes a water molecule to lose a H+ ion turning the solution acidic

Silicon chloride

  • SiCl4 is hydrolysed in water, releasing white fumes of hydrogen chloride gas in a rapid reaction

SiCl4 (l) + 2H2O (l) → SiO2 (s) + 4HCl (g)

  • The SiO2 is seen as a white precipitate and some of the hydrogen chloride gas produced dissolves in water to form an acidic solution

Phosphorus(V) chloride

  • PCl5 also gets hydrolysed in water

PCl5 (s) + 4H2O (l) → H3PO4 (aq) + 5HCl (g)

  • Both H3PO4 and dissolved HCl are highly acidic

Structures of ions

  • When P4O10 and PCl5 react with water the PO43- ion is formed

PO43- ion

A diagram to show the phosphate ion
The phosphate anion present in phosphoric(V) acid

  • When SO2 and SO3 react with water the SO32- and SO42- ions are formed respectively

SO32- ion

A diagram to show the structure of the sulftae(IV ) ion
The sulfate(IV) anion

SO42- ion

A diagram to show the structure of the sulfate(VI) anion
The sulfate(VI) ion

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