OXYGEN

a) Occurrence.

1. Fifty 50% of the earth’s crust consist of Oxygen combined with other elements e.g. oxides of metals
2. About 70% of the earth is water made up of Hydrogen and Oxygen.
3. About 20% by volume of the atmospheric gases is Oxygen that form the active part of air.

b) School laboratory preparation

Oxygen was first prepared in 1772 by Karl Scheele and later in 1774 by Joseph Priestly. It was Antony Lavoisier who gave it the name “Oxygen”

Procedure

Method 1: Using Hydrogen peroxide

Half fill a trough/basin with tap water.

Place a bee hive shelf/stand into the water.

Completely fill the gas jar with water and invert in onto the bee hive shelf/stand.

Clamp a round bottomed flask and set up the apparatus as below.

Collect several gas jars of Oxygen covering each sample.

Sample observation questions

1. What is observed when the hydrogen peroxide is added into the flask

Rapid effervescence/bubbling/fizzing

2. Describe the colour and smell of the gas

Colourless and odourless.

3. (a)Name the method of gas collection used.

-Over water

-Upward delivery

-Down ward displacement of water

(b) What property of Oxygen make it to be collected using the method above

-Slightly soluble in water

4. What is the purpose of manganese(IV)oxide?

Manganese(IV)oxide is catalyst.

A catalyst is a substance that speeds up the rate of a chemical reaction but remain chemically unchanged at the end of the reaction. Hydrogen peroxide decomposes slowly to form water and Oxygen gas. A little Manganese(IV)oxide speeds up the rate of decomposition by reducing the time taken for a given volume of Oxygen to be produced.

5. Write the equation for the reaction.

Hydrogen peroxide -> Water+ Oxygen 2H₂O₂ (aq) -> 2H₂ O (l) + O₂ (g)

6. Lower a glowing splint slowly into a gas jar containing Oxygen gas. State what is observed.

The glowing splint relights/rekindles

Oxygen relights/rekindles a glowing splint.

This is the confirmatory test for the presence of Oxygen gas

Method 1: Using Sodium peroxide

Half fill a trough/basin with tap water. Add four drops of phenolphthalein indicator. Place bee hive shelf/stand into the water.

Completely fill a gas jar with water and invert in onto the bee hive shelf/stand. Clamp a round bottomed flask and set up the apparatus as below.

Collect several gas jars of Oxygen covering each sample.

Sample observation questions

1. What is observed when water is added

(i) into the flask containing sodium peroxide

Rapid effervescence/bubbling/fizzing

(ii) phenolphththalein

Remains colourless/Phenolphthalein indicator is colourless in neutral solution

2. Describe the colour and smell of the gas

Colourless and odourless.

3. (a)Name the method of gas collection used.

-Over water. Oxygen is slightly soluble in water.

4. Test the gas by lowering a glowing splint slowly into a gas jar containing the prepared sample.

The glowing splint relights/rekindles. This confirms the presence of Oxygen gas 5.Write the equation for the reaction.

Sodium peroxide + Water -> Sodium hydroxide +Oxygen

2Na₂O₂ (aq) + 2H₂O (l) -> 4NaOH(aq) + O₂ (g)

1. Test the gas by lowering a glowing splint slowly into a gas jar containing the prepared sample.

The glowing splint relights/rekindles.

This confirms the presence of Oxygen gas

2. Write the equation for the reaction. Potassium Chlorate(V) -> Potassium Chloride + Oxygen

2KClO₃ (aq) -> 2KCl(aq) + 3O₂ (g)

3. What is the purpose of manganese(IV)oxide?

Manganese(IV)oxide is catalyst.

A catalyst is a substance that speeds up the rate of a chemical reaction but remain chemically unchanged at the end of the reaction. Potassium Chlorate(V) decomposes slowly to form potassium chloride and Oxygen gas. A little Manganese(IV)oxide speeds up the rate of decomposition by reducing the time taken for a given volume of Oxygen to be produced.