Heating of lead nitrate

   When we heat lead nitrate crystals a brown gas will be given off and a yellow solid will be formed. This gas is called Nitrogen dioxide and the yellow solid is the Lead oxide.

                      HEAT

Pb(NO3)2                          PbO + NO2 +O2

Heating of copper(ii)sulphate

     Copper(ii)sulphate crystals are heated in a hard glass test tube. The blue crystals turn white and water is given of which is collected in the second test tube. this type of occurring reaction is called a Reversible reaction.

                                  HEAT

CuSO.H2O(s)                                CuSO4(s) + H2O(l)

Reactions with oxygen of the air

• The composition of the air

    Oxygen constitutes 21% of the air by volume. It is described as the active part of air, this is because many chemical processes such as respiration(breathing) ,combustion(burning), and corrosion(rusting) take place in the air due to the presence of oxygen in the air.

AN EXPERIMENT TO DETERMINE THE PERCENTAGE BY VOLUME OF OXYGEN IN AIR

• Aim: To determine the percentage of oxygen in air by using the rusting of iron sponge(steel wool)
• Apparatus

• 10ml measuring cylinder
• Beaker
• Iron sponge
• Vinegar
• Water

• Diagram:

Figure: As the iron sponge rust it uses up the oxygen in the airin the measuring cylinder

• Method

• Rinse a small piece of iron sponge in dilute vinegar and shake off the excess liquid. ( the vinegar will assist in the rusting process)
• Push the iron sponge down the measuring cylinder to the bottom. Make sure that its fits tightly and will not slide down when the measuring cylinder is turned upside down.
• Fill a third beaker with water
• Place the measuring cylinder with the iron sponge upside down in the beaker.
• Leave the experiment undisturbed for at least 2 days
• After 2 days, notice that the water level has risen inside the measuring cylinder. Read water level on measuring cylinder.
• Calculate the volume of oxygen that was used by the iron sponge to rust.

• Result:

The iron sponge rusts according to the following equation;

4Fe + 3O2                           2Fe2O3

• CONCLUSION:

• As the oxygen in the air in the measuring cylinder reacts with iron to form IRON OXIDE, the volume of the trapped air decreases and water enters the measuring cylinder.
• This change in volume is equal to the volume of oxygen used in the reaction. You can read off the volume of oxygen used on the side of the measuring cylinder. It should be about 2ml. this means that the percentage of oxygen in the air was 20%.

Note: other components of air include; nitrogen, argon, krypton and xenon.

Separating the components of air

          Due to the boiling point of each gas present in air, they can be separated each by a process called FRACTIONAL DISTILLATION.

Fractional distillation of air follows a number of steps, therefore it can’t be done in a school laboratory. 

The fractional distillation process:

Figure; Fractional distillation of liquid air: different liquids have different boiling point.

Note: argon, krypton and xenon are Noble Gases.