Form 1:
Air and Combustion

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Reaction of non metals with Oxygen/air

The following experiments show the reaction of non metals with Oxygen and air.

I. Burning Carbon

Procedure

(a)Using a pair of tongs hold a dry piece of charcoal on a Bunsen flame. Observe.

Place the products in a beaker containing about 2cm3 of water. Test the solution/mixture using litmus papers

(b)Using a pair of tongs hold another piece of dry charcoal on a Bunsen flame.

Quickly lower it into a gas jar containing Oxygen gas .

Observe.

Place about 2cm3 of water.

Swirl.

Test the solution/mixture using litmus papers

Observations

-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.

Explanation

Carbon burns in air and faster in Oxygen with a blue non-sooty/non-smoky flame forming Carbon (IV) oxide gas.

Carbon burns in limited supply of air with a blue non-sooty/non-smoky flame forming Carbon (II) oxide gas.

Carbon (IV) oxide gas dissolves in water to form weak acidic solution of Carbonic (IV) acid.

Chemical Equation

Carbon + Oxygen -> Carbon (IV) oxide (excess air/oxygen)
C(s) + O2 (g) -> CO2 (g) (in excess air)

Carbon + Oxygen -> Carbon (II) oxide (limited air/oxygen)
2C(s) + O2 (g) -> 2CO (g) (in limited air)

Carbon (IV) oxide + Water -> Carbonic (IV) acid
CO2 (g) + H2O (l) -> H2CO3 (aq) (very weak acid)

II. Burning Sulphur

Procedure

(a)Using a deflagrating spoon place sulphur powder on a Bunsen flame. Observe.

Place the products in a beaker containing about 3cm3 of water.

Test the solution/mixture using litmus papers

(b) Using a deflagrating spoon place sulphur powder on a Bunsen flame.

Slowly lower it into a gas jar containing Oxygen gas.

Observe.

Place about 5cm3 of water. Swirl. Test the solution/mixture using litmus papers.

Observations

-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.

Explanation

Sulphur burns in air and faster in Oxygen with a blue non-sooty/non-smoky flame forming Sulphur (IV) oxide gas.

Sulphur (IV) oxide gas dissolves in water to form weak acidic solution of Sulphuric (IV) acid.

Chemical Equation

Sulphur + Oxygen -> Sulphur (IV) oxide
S(s) + O2 (g) -> SO2 (g) (in excess air)

Sulphur (IV) oxide + Water -> Sulphuric (IV) acid
SO2 (g) + H2O (l) -> H2SO3 (aq) (very weak acid)

III. Burning Phosphorus

Procedure

(a)Remove a small piece of phosphorus from water and using a deflagrating spoon (with a lid cover) place it on a Bunsen flame.

Observe.

Carefully put the burning phosphorus to cover gas jar containing about 3cm3 of water.

Test the solution/mixture using litmus papers

(b) Remove another small piece of phosphorus from water and using a deflagrating spoon (with a lid cover) place it on a Bunsen flame.

Slowly lower it into a gas jar containing Oxygen gas with about 5 cm3 of water.

Observe.

Swirl.

Test the solution/mixture using litmus papers.

Observations

-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.
Red litmus paper remains red.

Explanation

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.

Phosphoric (V) oxide gas dissolves in water to form weak acidic solution of Phosphoric (V) acid.

Chemical Equation

Phosphorus + Oxygen -> Phosphorous (V) oxide
4P(s) + 5O2 (g) -> 2P2O5(s)

Phosphorous (V) oxide + Water -> Phosphoric (V) acid
P2O5(s) + 3H2O (l) -> 2H3PO4 (aq) (very weak acid)

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