Chemical Properties of Oxygen

Introduction to Chemical Properties of Oxygen

– Oxygen is a very reactive non metal.
– Many elements react with oxygen through burning to form a group of compounds called oxides.
– Burning/combustion is the reaction of Oxygen with an element/substances.
– Reaction in which a substance is added oxygen is called Oxidation reaction
– Burning/combustion are an example of an oxidation reaction.
a) Most non metals burn in Oxygen/air to form an Oxide which in solution / dissolved in water is acidic in nature.
b) Some non metals burn in Oxygen/air to form an Oxide which in solution / dissolved in water is neutral in nature.
c) All metals burn in Oxygen/air to form an Oxide which in solution/dissolved in water is basic/alkaline in nature.

– Cut a 2cm length piece of magnesium ribbon.
– Using a pair of tongs introduce it to a Bunsen flame.
– Remove it when it catches fire and observe.
– Place the products in a beaker containing about 5cm3 of water. Test the solution/mixture using litmus papers
– Repeat the experiment using pure oxygen in place of air

NOTES:
When the ribbon is burnt in air, it burns with a bright blinding flame in air forming white solid/ash /powder. Effervescence/bubbles/ fizzing Pungent smell of urine. Blue litmus paper remains blue. Red litmus paper turns blue

When the ribbon is burnt in pure oxygen, it burns faster with a very bright blinding flame pure oxygen forming white solid/ash /powder. No effervescence/bubbles/ fizzing. No pungent smell of urine. Blue litmus paper remains blue. Red litmus paper turns blue

Magnesium burns in air producing enough heat energy to react with both Oxygen and Nitrogen to form Magnesium Oxide and Magnesium nitride. Both Magnesium Oxide and Magnesium nitride are white solid/ash /powder.

The following are chemical equations showing the reactions.
Magnesium + Oxygen  Magnesium Oxide
2Mg(s) + O₂(g)  2MgO(s)

Magnesium + Nitrogen  Magnesium Nitride
3Mg(s) + N₂(g)  Mg₂N₂ (s)

Magnesium Oxide dissolves in water to form a basic/alkaline solution of Magnesium hydroxide
Magnesium Oxide + Water  Magnesium hydroxide
MgO(s) + H2O (l)  Mg(OH)₂ (aq)

Magnesium Nitride dissolves in water to form a basic/alkaline solution of Magnesium hydroxide and producing Ammonia gas. Ammonia is also an alkaline/basic gas that has a pungent smell of urine.
Magnesium Nitride + Water  Magnesium hydroxide + Ammonia gas
Mg₃N₂ (s) + 6H₂O (l)  3Mg (OH)₂ (aq) + 2NH₃(g)

B. Burning Sodium

The experiment should be undertaken as follows;
– Carefully cut a very small piece of sodium.
– Using a deflagrating spoon introduce it to a Bunsen flame.
– Remove it when it catches fire and observe
– Place the products in a beaker containing about 20cm3 of water. Test the solution/mixture using litmus papers.
– Repeat the experiment using pure oxygen

NOTES:
When burnt in air, sodium burns with a yellow flame in air forming a black solid. Blue litmus paper remains blue. Red litmus paper turns blue

When burnt in pure oxygen, sodium burns faster with a golden yellow flame in pure oxygen forming a yellow solid. Effervescence/bubbles/ fizzing. Gas produced relights glowing splint. Blue litmus paper remains blue. Red litmus paper turns blue.

Sodium burns in air forming black Sodium Oxide
Sodium + Oxygen/air  Sodium Oxide
4Na(s) + O₂ (g)  2Na₂O(s)

Sodium Oxide dissolves in water to form a basic/alkaline solution of Sodium hydroxide.
Sodium Oxide + Water  Sodium hydroxide
Na₂O(s) + H₂O (l)  2NaOH (aq)

Sodium burns in pure oxygen forming yellow Sodium peroxide
Sodium + Oxygen  Sodium peroxide
2Na(s) + O₂ (g)  Na₂O₂ (s)

Sodium peroxide dissolves in water to form a basic/alkaline solution of Sodium hydroxide. Oxygen is produced.
Sodium Oxide + Water  Sodium hydroxide + Oxygen
2Na₂O₂ (s) + 2H₂O (l)  4NaOH (aq) + O₂ (l)

C. Burning Calcium

The experiment should be undertaken as follows;
– Using a pair of tongs hold the piece of calcium on a bunsen flame and observe.
– Place the products in a beaker containing about 2cm3 of water.
– Test the solution/mixture using litmus papers.
– Repeat the experiment using pure oxygen

NOTES:
Calcium burns in air with difficulty producing a faint red flame in air forming a white solid. Blue litmus paper remains blue. Red litmus paper turns blue

Calcium burns in oxygen with difficulty producing a less faint red flame Oxygen forming a white solid. Blue litmus paper remains blue. Red litmus paper turns blue

Calcium burns in air forming white calcium Oxide. Calcium Oxide coat/cover the calcium preventing further burning.
Calcium + Oxygen/air  Calcium Oxide
2Ca(s) + O₂(g)  2CaO(s)

Small amount of Calcium Oxide dissolves in water to form a basic/alkaline solution of Calcium hydroxide. The common name of Calcium hydroxide is lime water.
Calcium Oxide + Water  Calcium hydroxide
CaO(s) + H₂O (l)  Ca(OH)₂ (aq)

D. Burning Iron

The experiment should be undertaken as follows;
– Using a pair of tongs hold the piece of Iron wool/steel wire on a Bunsen flame and observe. – Place the products in a beaker containing about 2cm3 of water.
– Test the solution/mixture using litmus papers.
– Repeat the experiment using pure oxygen

NOTES:
Iron wool/steel wire burns producing an Orange flame in air forming a brown solid. Blue litmus paper remains blue. Red litmus paper turns faint blue

Iron wool/steel wire burns producing a golden Orange flame in Oxygen forming a Brown solid. Blue litmus paper remains blue. Red litmus paper turns faint blue

Iron burns in air forming brown Iron (III) Oxide
Iron + Oxygen/air  Iron (III) Oxide
4Fe(s) + 3O₂ (g)  2Fe₂O₃(s)

Very small amount of Iron (III) Oxide dissolves in water to form a weakly basic/alkaline brown solution of Iron (III) hydroxide.
Iron (III) Oxide + Water  Iron (III) hydroxide
Fe₂O₃(s) + 3H₂O (l)  2Fe(OH)₃ (s)

E. Burning Copper

The experiment should be undertaken as follows;
– Using a pair of tongs hold the piece of copper turnings/shavings on a Bunsen flame and observe
– Place the products in a beaker containing about 2cm3 of water.
– Test the solution/mixture using litmus papers.
– Repeat the experiment using pure oxygen

NOTES:
Copper turnings/shavings burns with difficulty producing a green flame in air forming a black solid. Blue litmus paper remains blue. Red litmus paper turns faint blue

Copper turnings/shavings burns less difficulty producing a green flame in Oxygen forming a Brown solid. Blue litmus paper remains blue. Red litmus paper turns faint blue

Copper burns in air forming black Copper (II) Oxide
Copper + Oxygen/air  Copper (II) Oxide
2Cu(s) + O₂ (g)  2CuO(s)

Very small amount of Copper (II) Oxide dissolves in water to form a weakly basic/alkaline blue solution of Copper (II) hydroxide.
Copper (II) Oxide + Water  Copper (II) hydroxide
CuO(s) + H₂O (l)  Cu (OH)₂ (s)

Reaction of non-metals with Oxygen/Air

A. Burning Carbon

The experiment should be undertaken as follows;
– Using a pair of tongs hold a dry piece of charcoal on a Bunsen flame and observe
– Place the products in a beaker containing about 2cm3 of water and swirl.
– Test the solution/mixture using litmus papers.
– Repeat the experiment using pure oxygen

NOTES:
Carbon chars then burns with a blue flame
Colourless and odorless gas produced
Solution formed turn blue litmus paper faint red. Red litmus paper remains red.

Carbon burns in air and faster in Oxygen with a blue non-sooty/non-smoky flame forming Carbon (IV) oxide gas.
Carbon + Oxygen  Carbon (IV) oxide (in excess air/oxygen)
C(s) + O₂ (g)  CO₂ (g) – (in excess air)

Carbon burns in limited supply of air with a blue non-sooty/non-smoky flame forming Carbon (II) oxide gas.
Carbon + Oxygen  Carbon (II) oxide – (in limited air/oxygen)
2C(s) + O₂ (g)  2CO (g) (in limited air)

Carbon (IV) oxide gas dissolves in water to form weak acidic solution of Carbonic (IV) acid.
Carbon (IV) oxide + Water  Carbonic (IV) acid
CO2 (g) + H₂O (l)  H₂CO₃ (aq) -(very weak acid)

B. Burning Sulphur

The experiment should be undertaken as follows;
– Using a deflagrating spoon, place sulphur powder on a Bunsen flame and observe.
– Place the products in a beaker containing about 3cm3 of water.
– Test the solution/mixture using litmus papers.
– Repeat the experiment using pure oxygen

NOTES:
Sulphur burns with a blue flame
Gas produced that has pungent choking smell
Solution formed turn blue litmus paper faint red. Red litmus paper remains red.

Sulphur burns in air and faster in Oxygen with a blue non-sooty/non-smoky flame forming Sulphur (IV) oxide gas.
Sulphur + Oxygen  Sulphur (IV) oxide – (in excess air)
S(s) + O₂ (g)  SO₂ (g)

Sulphur (IV) oxide gas dissolves in water to form weak acidic solution of Sulphuric (IV) acid. Sulphur (IV) oxide + Water  Sulphuric (IV) acid – (a weak acid)
SO₂ (g) + H₂O (l)  H₂SO₃ (aq)

C. Burning Phosphorus

The experiment should be undertaken as follows;
– Remove a small piece of phosphorus from water and using a deflagrating spoon (with a lid cover) places it on a Bunsen flame and observe. – Carefully put the burning phosphorus to cover gas jar containing about 3cm3 of water.
– Test the solution/mixture using litmus papers.
– Repeat the experiment using pure oxygen

NOTES:
Phosphorus catches fire before heating on Bunsen flame
Dense white fumes of a gas produced that has pungent choking poisonous smell
Solution formed turn blue litmus paper faint red, and red litmus paper remains red.

Phosphorus is stored in water.
On exposure to air it instantaneously fumes then catch fire to burn in air and faster in Oxygen with a yellow flame producing dense white acidic fumes of Phosphorus (V) oxide gas.
Phosphorus + Oxygen  Phosphorous (V) oxide
4P(s) + 5O₂ (g)  2P₂O₅(s)

Phosphoric (V) oxide gas dissolves in water to form weak acidic solution of Phosphoric (V) acid.
Phosphorous (V) oxide + Water  Phosphoric (V) acid – (weak acid)
P₂O₅(s) + 3H2O (l)  2H₃PO₄ (aq)

Reactivity Series/Competition for Combined Oxygen

The reactivity series is a list of elements/metals according to their affinity for oxygen.
Some metals have higher affinity for Oxygen than others.
A metal/element with higher affinity for oxygen is placed higher/on top of the one less affinity.

The table below shows the reactivity series of metals and other elements

– The most reactive is potassium and the least reactive is platinum.

Metals compete for combined Oxygen. A metal/element with higher affinity for oxygen removes Oxygen from a metal lower in the reactivity series/less affinity for Oxygen.

1. When a metal/element gains/acquire Oxygen, the process is called Oxidation.
2. When metal/element donate/lose Oxygen, the process is called Reduction.
3. An element/metal/compound that undergoes Oxidation is called Reducing agent.
4. An element/metal/compound that undergoes Reduction is called Oxidizing agent.
5. A reaction in which both Oxidation and Reduction take place is called a Redox reaction

Redox reaction between Magnesium and copper (II) Oxide

Magnesium is higher in the reactivity series than Copper.
It has therefore higher affinity for Oxygen than copper.
When a mixture of copper (II) oxide and Magnesium is heated, Magnesium reduces copper (II) oxide to brown copper metal and itself oxidized to Magnesium oxide.
Copper (II) oxide + Magnesium  Magnesium oxide + Copper
CuO(s) + Mg(s)  MgO(s) + Cu(s)

Magnesium is the reducing agent because it undergoes oxidation process.
Copper (II) oxide is the oxidizing agent because it undergoes redox reduction process.
The reaction of Magnesium and Copper (II) oxide is a redox reaction

POINT TO NOTE: The reactivity series is used during extraction of metals from their ore.
An ore is a rock containing mineral element which can be extracted for commercial purposes.