Reactions of the Period 3 Oxides & Chlorides (Oxford AQA International A Level (IAL) Chemistry): Revision Note
Exam code: 9622
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 |
MgO | MgO (s) + H2O (l) → Mg(OH)2 (aq) | 10 |
Al2O3 | No reaction | - |
SiO2 | No reaction | - |
P4O10 | P4O10 (s) + H2O (l) → 4H3PO4 (aq) | 2 |
SO2 | SO2 (g) + H2O (l) → H2SO3 (aq) | 1 |
SO3 | SO3 (g) + H2O (l) → H2SO4 (aq) | 1 |
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 |
|---|---|---|---|---|---|---|
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) | Reacts with acid to form salt and water
|
SiO2 | SiO2 (s) + 2NaOH (aq) → Na2SiO3 (aq) + H2O (l) |
|
P4O10 | P4O10 (s) + 12NaOH (aq) → 4Na3PO4 (aq) + 6H2O (l) | |
SO2 | SO2 (g) + 2NaOH (aq) → Na2SO3 (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
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
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
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
When SO2 and SO3 react with water the SO32- and SO42- ions are formed respectively
SO32- ion
SO42- ion
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