1. Reactions of Period 3 Elements with Oxygen
Sodium
Sodium burns in oxygen with an orange flame
to produce a white solid mixture of sodium
oxide and sodium peroxide.
For the simple oxide: 4Na(s) + O2(g) --->
2Na2O(s)
For the peroxide: 2Na(s) + O2(g) --->
Na2O2(s)
3. Magnesium
Magnesium burns in oxygen
with an intense white flame
to give white solid
magnesium oxide.
Note: If magnesium is
burns in air rather than
in pure oxygen, it also
reacts with the nitrogen
in the air. You get a
mixture of magnesium
oxide and magnesium
nitride formed.
4. Aluminium
Aluminium will burn in oxygen if it is
powdered, otherwise the strong oxide layer
on the aluminium tends to inhibit the
reaction. If you sprinkle aluminium powder
into a Bunsen flame, you get white sparkles.
White aluminium oxide is formed.
6. • The metals, sodium, magnesium and aluminium are strong reducing
agents. When they react with oxygen, they readily give up electrons in
their most outermost shells to form positive ions.
Na(s) -> Na+(g) + e-
Mg(s) -> Mg2+(g) +2e-
Al(s) -> Al3+(g) + 3e-
In these reactions, oxygen acts as an oxidising agent. The oxygen molecule
accepts electrons to form oxide ions.
O2(g) - 2e- --> O2-(g)
The metal ions and oxide ions then combine to form ionic oxides.
7. The non-metals, silicon, phosphorus and sulphur are weak
reducing agents.
• Silicon is the weakest
reducing agent and
hence reacts slowly
with oxygen. It burns
in oxygen at red heat
to form silicon(IV)
oxide
8. Phosphorus
White phosphorus catches fire spontaneously in air, burning with a white flame and producing clouds of white
smoke - a mixture of phosphorus(III) oxide and phosphorus(V) oxide.
The proportions of these depend on the amount of oxygen available. In an excess of oxygen, the product will be
almost entirely phosphorus(V) oxide.
For the phosphorus(III) oxide:
For the phosphorus(V) oxide:
9. Sulphur
Sulphur burns in air or oxygen on
gentle heating with a pale blue
flame. It produces colourless
sulphur dioxide gas.
Note: Sulphur dioxide can,
of course, be converted
further into sulphur trioxide
in the presence of oxygen,
but it needs the presence of
a catalyst and fairly carefully
controlled conditions.
10. • Chlorine is a strong oxidising agent. Thus, chlorine does not react with
oxygen. Oxides of chlorine such as dichlorine monoxide (Cl2O) and
chlorine dioxide (ClO2) cannot be prepared by the reaction of
chlorine and oxygen.
Argon is a noble gas and does not react with oxygen.
11. Reactions of Period 3 Elements with Water
• Sodium has a very exothermic reaction with cold water
producing hydrogen and a colourless solution of sodium
hydroxide.
•
12. Magnesium
Magnesium has a very slight reaction with cold water, but burns in steam.
A very clean coil of magnesium dropped into cold water eventually gets covered in small bubbles of hydrogen which
float it to the surface. Magnesium hydroxide is formed as a very thin layer on the magnesium and this tends to stop
the reaction.
Magnesium burns in steam with its typical white flame to produce white magnesium oxide and hydrogen.
13. Aluminium
Aluminium powder heated in steam produces hydrogen and
aluminium oxide. The reaction is relatively slow because of
the existing strong aluminium oxide layer on the metal, and
the build-up of even more oxide during the reaction.
14. • Silicon, Phosphorus, sulphur and argon do not react with water or
steam.
Chlorine
Chlorine dissolves in water to some
extent to give a green solution. A
reversible reaction takes place to
produce a mixture of hydrochloric
acid and chloric(I) acid
(hypochlorous acid).
Chlorine is both simultaneously reducing
and oxidising. Disproportionation is the name
for the reaction where an element
simultaneously oxidises and reduces.
15. ACIDIC AND BASIC PROPERTIES OF
OXIDES AND HYDROLYSIS OF
OXIDES
Acidic and basic properties of the oxides of Period 3 elements
16. Hydrolysis of Oxides
-chemical reaction of a compound with water
1. Na2O (Sodium Oxide)
◦ Soluble in water
◦ Reacts with water to form alkaline solution
◦ pH value- 11-14
◦ Eq: Na2O(s) + H2O(l) 2NaOH(aq)
17. 2.) MgO (Magnesium Oxide)
◦ Sparingly soluble
◦ Reacts with water to produce alkaline solution
◦ pH value- 9-11
◦ Eq: MgO(s) + H2O(l) Mg(OH)2
18. ◦ 3.)Al2O3 (Aluminum Oxide)
◦ Aluminum oxide doesn’t react with water in room temperature because it has a giant
ionic structure with a high degree of covalent bonding.
◦ Insoluble in water.
◦ It is amphoteric, reacting with both to acid and base.
◦ 4.)SiO2 (Silicon(IV) Oxide)
◦ Silicon dioxide doesn't react with water, because of the difficulty of breaking giant
covalent structures.
◦ It doesn’t have basic properties, instead it is a weak acid.
19. 5.) Oxides of phosphorus
a.) Phosphorus (III) oxide
◦ Dissolves in cold water to form phosphorus acid, H3PO4, which is a
weak acid.
◦ Eq: P4O6(s) + 6H2O(l) 4H3PO3(aq)
b.) Phosphorus (IV) oxide
• Reacts violently with water to produce a solution containing a mixture
of acids.
• pH value – 1
• Eq: P4O10(s) + 6H2O 4H3PO4(aq)
20. 6.) Oxides of sulphur
a.) Sulphur dioxide, SO2
◦ Fairly soluble in water
◦ Reacts with water to form sulphurous acid, H2SO3
◦ pH value – 1
◦ Eq: SO2(g) + H2O(l) H2SO3(aq)
b.) Sulphur trioxide, SO3
◦ Reacts violently with water to produce a fog of concentrated sulphuric acid droplets
◦ Strong acid
◦ pH value – 0
◦ Eq: SO3(g) + H2O(l) H2SO4(aq)
21. 7.) Oxides of Chlorine
a.) Dichlorine monoxide, Cl2O
◦ A yellow gas
◦ Reacts with water to produce chloric(I) acid also known as hypochlorous acid
◦ Eq: Cl2O(g) + H2O 2HClO(aq)
b.) Chlorine dioxide, (ClO2)
◦ A reddish-yellow gas
◦ Reacts with water to form chloric (III) acid (HClO2) and chloric (V) acid (HClO3)
◦ Eq: 2ClO2(g) + H2O(l) HClO2(aq) +HClO3(aq)
c.)Dichlorine heptoxide (Cl2O7)
◦ Dissolves in water to form chloric (VII) acid (HClO4)
◦ Eq: Cl2O7(l) + H2O(l) 2HClO4
22. Acidic and basic properties of the oxides
of period 3 elements
Sodium oxide, Na2O & Magnesium oxide, MgO
◦ Soluble in acids but insoluble in alkalis
◦ Dissolves in acids to form salt and water
◦ Eq: Na2O(s) + 2HCl(aq) 2NaCl(aq) + H2O(l)
MgO(s) + H2SO4(aq) MgSO4(aq) + H2O(l)
◦ They have properties of an alkaline
23. Aluminium oxide, Al2O3
◦ Does not react with water but with both alkalis and acid
◦ Reacts with hydrochloric acid to form aluminum chloride
Eq: Al2O3(s) + 6HCl(aq) 2AlCl3(aq) + H2O(l)
◦ Reacts with sodium hydroxide to form sodium aluminate,
NaAl(OH)4
Eq: Al2O3(s) + 2NaOH(aq) + 3H2O(l) 2NaAl(OH)4(aq)
◦ It is an amphoteric
24. Silicon (IV) Oxide
◦ Does not react with water or acid
◦ Dissolves in hot, concentrated sodium hydroxide NaOH to form sodium
silicate and water
◦ Eq: SiO2(s) + 2NaOH(aq) Na2SiO3(aq) + H2O(l)
25. Oxides of phosphorus, sulphur and chlorine
◦ Does not react with acids or water
◦ React with alkalis to form water and salt
Oxides of phosphorus
◦ Eq: P4O6(l) + 12NaOH(aq) 4Na3PO3(aq) sodium phosphate (III) + 6H2O(l)
P4O10(l) +12NaOH(aq) 4Na3PO4(aq)sodium phosphate (IV) +6H2O(l)
Oxides of sulphur
◦ Eq: SO2(s) + 2NaOH(g) Na2SO3(aq) sodium sulphite +6H2O
SO3(s) +2NaOH(g) Na2SO4(aq) sodium sulphate + 6H2O
Oxides of chlorine
◦ Eq: Cl2O(g) +2NaOH(aq) 2NaOCl(aq)sodium chlorate(I) +H2O(l)
Cl2O7(l) + 2NaOH(aq) 2NaClO4(aq) sodium chlorate (VII) + H2O(l)
26. Acidic and basic properties of the oxides
of period 3 elements
Formula
of oxide
Na2O MgO Al2O3 SiO2 P4O10
P4O6
SO3
SO2
Cl2O7
Cl2O
Acid-
Base
Property
Base Base Amphoteric Acid Acid Acid Acid
27. Reactions of the oxides of Period 3
elements with water
Oxides Na2O MgO Al2O3 SiO2 P4O10
P4O6
SO3
SO2
Cl2O7
Cl2O
ClO2
Solubility
in water
Soluble Sparingly
soluble
Insoluble Insoluble Soluble Soluble Soluble
Reaction
with water
Forms
alkaline
solution
Forms
alkaline
solution
No
reaction
No
reaction
Forms
acidic
solution
Forms
acidic
solution
Forms
acidic
solution
ph value 11-14 9-11 - - P4O10 - 1 0 0
28. Classifications of the oxides of Period 3 elements
as basic, amphoteric or acidic based on their
reactions with water, acid and alkali
29. Sodium oxide
• Sodium oxide is a simple strongly basic oxide. It is basic because it contains the
oxide ion, O2-, which is a very strong base with a high tendency to combine with
hydrogen ions.
Reaction with water: Sodium oxide reacts exothermically with cold water to
produce sodium hydroxide solution. A concentrated solution of sodium oxide in
water will have pH 14.
• Na2O+H2O→2NaOH
Reaction with acids: As a strong base, sodium oxide also reacts with acids. For
example, it reacts with dilute hydrochloric acid to produce sodium chloride
solution.
• Na2O+2HCl→2NaCl+H2O
30. Magnesium oxide
• Magnesium oxide is another simple basic oxide, which also contains oxide ions.
However, it is not as strongly basic as sodium oxide because the oxide ions are
not as weakly-bound.
Reaction with water: At first glance, magnesium oxide powder does not appear
to react with water. However, the pH of the resulting solution is about 9,
indicating that hydroxide ions have been produced. Some magnesium hydroxide
is formed in the reaction, but as the species is almost insoluble, few hydroxide
ions actually dissolve. The reaction is shown below:
• MgO+H2O→Mg(OH)2
Reaction with acids: Magnesium oxide reacts with acids as predicted for a simple
metal oxide. For example, it reacts with warm dilute hydrochloric acid to give
magnesium chloride solution.
• MgO+2HCl→MgCl2+H2O
31. Aluminium oxide
• Aluminium oxide is amphoteric. It has reactions as both a base and an acid.
• Reaction with water: Aluminum oxide is insoluble in water and does not react like
sodium oxide and magnesium oxide. The oxide ions are held too strongly in the solid
lattice to react with the water.
• Reaction with acids: Aluminum oxide contains oxide ions, and thus reacts with acids in
the same way sodium or magnesium oxides do. Aluminum oxide reacts with hot dilute
hydrochloric acid to give aluminum chloride solution.
• Al2O3+6HCl→2AlCl3+3H2O
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. This is possible because the
electronegativity difference between aluminum and oxygen is small, unlike the difference
between sodium and oxygen, for example (electronegativity increases across a period)
• Aluminum oxide reacts with hot, concentrated sodium hydroxide solution to produce a
colorless solution of sodium tetrahydroxoaluminate:
• Al2O3+2NaOH+3H2O→2NaAl(OH)4
32. Silicon dioxide (silicon(IV) oxide)
• Silicon is too similar in electronegativity to oxygen to form ionic bonds. Therefore,
because silicon dioxide does not contain oxide ions, it has no basic properties. In
fact, it is very weakly acidic, reacting with strong bases.
Reaction with water: Silicon dioxide does not react with water, due to the
thermodynamic difficulty of breaking up its network covalent structure.
Reaction with bases: Silicon dioxide reacts with hot, concentrated sodium
hydroxide solution, forming a colorless solution of sodium silicate:
• SiO2+2NaOH→Na2SiO3+H2O
• In another example of acidic silicon dioxide reacting with a base, the Blast
Furnace extraction of iron, calcium oxide from limestone reacts with silicon
dioxide to produce a liquid slag, calcium silicate:
• SiO2+CaO→CaSiO3
33. The phosphorus oxides
• Two phosphorus oxides, phosphorus(III) oxide, P4O6, and phosphorus(V) oxide,
P4O10, are considered here.
Phosphorus(III) oxide: Phosphorus(III) oxide reacts with cold water to produce a
solution of the weak acid, H3PO3—known as phosphorous acid,
orthophosphorous acid or phosphonic acid:
• P4O6+6H2O→4H3PO3P4O6+6H2O→4H3PO3
• The fully-protonated acid structure is shown below:
34. • Phosphorus(III) oxide is unlikely to be reacted directly with a base. In
phosphorous acid, the two hydrogen atoms in the -OH groups are acidic, but
the third hydrogen atom is not. Therefore, there are two possible reactions
with a base like sodium hydroxide, depending on the amount of base added:
• NaOH+H3PO3→NaH2PO3+H2O
• 2NaOH+H3PO3→Na2HPO3+2H2O
• In the first reaction, only one of the protons reacts with the hydroxide ions
from the base. In the second case (using twice as much sodium hydroxide),
both protons react.
• If instead phosphorus(III) oxide is reacted directly with sodium hydroxide
solution, the same salts are possible:
• 4NaOH+P4O6+2H2O→4NaH2PO3
• 9NaOH+P4O6→4Na2HPO3+2H2O
35. Phosphoric (V) oxide
• Phosphoric (V) oxide is also unlikely to be reacted directly with a base, but the
hypothetical reactions are considered. In its acid form, molecule has three acidic -
OH groups, which can cause a three-stage reaction with sodium hydroxide:
• NaOH+H3PO4→NaH2PO4+H2O
• 2NaOH+H3PO4→Na2HPO4+2H2O
• 3NaOH+H3PO4→Na3PO4+3H2O
• Similar to phosphorus (III) oxide, if phosphorus(V) oxide reacts directly with
sodium hydroxide solution, the same possible salt as in the third step (and only
this salt) is formed:
• 12NaOH+P4O10→4Na3PO4+6H2O
36. The sulphur oxides
• Two oxides are considered: sulfur dioxide, SO2, and sulfur trioxide, SO3.
Sulfur dioxide: Sulfur dioxide is fairly soluble in water, reacting to give a solution
of sulfurous acid (also known as sulfuric(IV) acid), H2SO3, as shown in the
reaction below. This species only exists in solution, and any attempt to isolate it
gives off sulfur dioxide.
• SO2+H2O→H2SO3SO2+H2O→H2SO3
• The protonated acid has the following structure:
37. The sulphur oxides
• Sulphur dioxide reacts directly with bases such as sodium hydroxide solution.
Bubbling sulphur dioxide through sodium hydroxide solution first forms sodium
sulphite solution, followed by sodium hydrogen sulphite solution if the sulphur
dioxide is in excess.
• SO2+2NaOH→Na2SO3+H2O
• Na2SO3+H2O→2NaHSO3
• Another important reaction of sulphur dioxide is with the base calcium oxide to
form calcium sulphite (also known as calcium sulphate(IV)). This is of the
important methods of removing sulphur dioxide from flue gases in power
stations.
• CaO+SO2→CaSO3
38. The sulphur oxides
• Sulfur trioxide: Sulfur trioxide reacts violently with water to produce a fog of
concentrated sulfuric acid droplets.
• SO3+H2O→H2SO4SO3+H2O→H2SO4
• Pure, fully-protonated sulfuric acid has the structure:
39. The sulphur oxides
• Sulphur trioxide
Pure, fully-protonated sulfuric acid has the structure:
• Sulfuric acid is a strong acid, and solutions will typically have a pH around 0. The
acid reacts with water to give a hydronium ion (a hydrogen ion in solution) and a
hydrogen sulfate ion. This reaction runs essentially to completion:
• H2SO4(aq)+H2O(l)→H3P++HSO−4(aq)
• The second proton is more difficult to remove. In fact, the hydrogen sulfate ion is
a relatively weak acid, similar in strength to the acids discussed above. This
reaction is more appropriately described as an equilibrium:
• HSO−4(aq)+H2O⇌H3O+(aq)+SO2−4(aq)
40. The chlorine oxides
• Chlorine forms several oxides, but only two (chlorine(VII) oxide, Cl2O7, and
chlorine(I)oxide, Cl2O) are considered here.
41. The chlorine oxides
• Chlorine(VII) oxide: Chlorine(VII) oxide is the highest oxide of chlorine— the
chlorine atom is in its maximum oxidation state of +7. It continues the trend of
the highest oxides of the Period 3 elements towards being stronger acids.
Chlorine(VII) oxide reacts with water to give the very strong acid, chloric(VII) acid,
also known as perchloric acid.
• Cl2O7+H2O→2HClO4
• Chloric(VII) acid reacts with sodium hydroxide solution to form a solution of
sodium chlorate(VII) :
• NaOH+HClO4→NaClO4+H2ONaOH+HClO4→NaClO4+H2O
• Chlorine(VII) oxide itself also reacts directly with sodium hydroxide solution to
give the same product:
• 2NaOH+Cl2O7→2NaClO4+H2O
42. The chlorine oxides
• Chlorine(I) oxide: Chlorine(I) oxide is far less acidic than chlorine(VII) oxide. It
reacts with water to some extent to give chloric(I) acid, HOCl−HOCl− also known
as hypochlorous acid.
• Cl2O+H2O⇌2HOCl
• Chlorine(I) oxide also reacts directly with sodium hydroxide to give the same
product:
• 2NaOH+Cl2O→2NaOCl+H2O
43. Use of sulphur dioxide in food
preservations
The process of preserving food with sulphur dioxide is intended to
provide a longer shelf life, kill harmful bacteria that might grow on
vegetation and foods, and help food products maintain a certain visual
appearance
44. As a germicide
• Sulphur dioxide (SO2) can be effective as a anti microbial agent.
• Prevents the growth of microbes
• The molecular form of SO2 (sulphur dioxide) is the most effective form and it has
been calculated that 0.8 ppm molecular SO2 is required to inhibit microbial
growth and activity
• Bacteria, in particular lactic acid bacteria (LAB), are very sensitive to SO2
45. As an antioxidant
• protecting wine from spoilage by bacteria and oxidation
• safeguarding the wine's fruit integrity and protecting it against browning
• preventing the oxidative colouration of white wine
• prevents naturally occurring enzymes in grapes that cause wines to brown (called
polyphenol oxidases)
46. As a preservative
• Sulfur dioxide is sometimes used as a preservative for dried apricots, dried figs,
and other dried fruits, owing to its antimicrobial properties. As a preservative, it
maintains the colorful appearance of the fruit and prevents rotting. It is also
added to sulfured molasses.
47. As a reducing agent
• In the presence of water, sulfur dioxide is able to decolorize substances
• Used as bleach for papers and delicate materials such as clothes
• used to treat chlorinated wastewater prior to release
• SO2 + H2O ⇌ HSO3
− + H+
48. • 1. Which of the Period 3 elements do not react with water at room
temperature, but reacts vigorously with steam? Write an equation for this
reaction.
• 2. Which element has an oxide which dissolves in water to form an acidic
solution?
A. Al
B. Na
C. P
D. Si
49. • 3. Which of these oxides is used in the food industry and for what
purpose is it being used?
A. SiO2
B. SO2
C. Na2O
D. Cl2O7
50. • 4. An oxide X has a melting point of 1600 degree celcius. It dissolves
in hot, aqueous sodium hydroxide but not in water or acid. Oxide X
could be
A. MgO
B. Al2O3
C. SiO2
D. P4O10
