Experiments to show the difference between air and oxygen when chemicals burn

1. Hold a piece of magnesium wire with a pair of tongs and burn it. Allow it to burn for some time. Observe what happens: Magnesium b in air with a sparkle, forming a white powder. This white powder is magnesium oxide.

2Mg + 0₂ -------------------> 2MgO

Magnesium + Oxygen -----> Magnesium oxide

A large amount of heat is generated in this reaction.

2. Take a few pieces- of charcoal in a deflagrating or combustion spoon. Heat the charcoal until it becomes red hot. Introduce it in a gas jar containing oxygen. Is any flame visible? Add 10 mL of freshly prepared limewater to the gas jar. What do you observe? The limewater turns milky.

The following chemical reaction takes place :

C  + 0₂--------------> C0₂

Carbon + Oxygen -------------> Carbon dioxide

The carbon dioxide formed in this reaction turns limewater milky. As you know, the carbon dioxide reacts with calcium hydroxide present in limewater and forms calcium carbonate. Calcium carbonate appears 'in the form of a white precipitate.

Ca(OH)₂ + Co₂----------> CaCO₃ + H₂0

Calcium hydroxide + Carbon dioxide      =           Calcium carbonate Water

3. Place a little sulphur in a deflagrating spoon. Hold it over the flame of a burner till

the sulphur melts and just begins to burn. Observe the flame of burning sulphur (Fig). Introduce the deflagrating spoon into a gas jar containing oxygen.

Sulphur, like charcoal, bums more vigorously in oxygen than in air. An oxide of sulphur, i.e. sulphur dioxide gas, is formed. Sulphur dioxide gas has a pungent smell.

The following chemical reaction takes place :

S     +      0₂ --------> S0₂

Sulphur + Oxygen   ----------->      Sulphur dioxide

A large amount of heat is liberated during the burning of sulphur.

4. Take a little red phosphorus in a deflagrating spoon. Heat it over the flame of burner till it catches fir How does it burn in air Introduce the deflagrating spoon containing burning phosphorus into a gas jar of oxygen. What do you observe? How does the phosphorus burn now?

Phosphorus burns in oxygen according to the following chemical equation :

4P + 50₂ = 2P₂0₅

Phosphorus + Oxygen   ------>     Phosphorus pentoxide

5. Steel also burns in oxygen without a flame, throwing out glittering sparks in all directions. For conducting this experiment, steel wire or steel wool is used.

The following chemical reaction takes place:

4Fe + 30₂ = 2Fe₂O₃

Iron  +  Oxygen      ------>         Iron oxide

From these activities, we can conclude that

(i) burning of substances is more vigorous in oxygen than in air, and oxygen is a very reactive substance.

(ii) an important chemical property of oxygen is its ability to combine with other substances to form oxides.