$obtained from liquid air by fractional distillation$

$obtained from liquid air by fractional distillation$

When it is heated in air, it turns black. In the combustion tube, at the end of the experiment, the red-brown copper turnings turn black.Ĭopper is a red-brown metal. Allow the glass tube to cool and record the volume of the gas in syringe A. Repeat this process while heating the copper turnings until the new volume of air in syringe A is constant. Slowly pass the air from syringe A through the hot turnings to syringe B and back. Heat the copper turnings until they are red hot. Connect the tube with two glass syringes with one syringe containing a specific volume of air while the other is empty. Pack copper turnings in a long hard glass tube about 6cm long. When copper is heated in air, it reacts with oxygen in air to form black copper (II) oxide. (b) Heating copper in a fixed volume of air

$obtained from liquid air by fractional distillation$

The component of air that is inactive is mainly nitrogen. The part of air that remains in the gas jar does not support combustion. The active part of air is oxygen, which forms about 20% of dry air by volume. Heating causes expansion of gases therefore the apparatus should be allowed to cool before the final reading is taken.The candle may go off before all the oxygen is used up due to the build-up of carbon (IV) oxide levels.The sodium hydroxide solution may not absorb all the carbon (IV) oxide gas.This is due to experimental errors, which may result from: The experimental result is not the same as the theoretical value of the percentage of oxygen in air by volume.Dilute sodium hydroxide is preferably used instead of water to absorb carbon (IV) oxide that was initially in the gas jar and that which is produced during combustion.Percentage of air by volume used up = × 100 Height of air used during burning = 3.1cm The percentage of air used up during the experiment can be determined as follows: Height of air column after burning = 12.9cm Height of air column before burning = 16.0cm The following are sample results for a similar experiment.

$obtained from liquid air by fractional distillation$

Greater atmospheric pressure acting on the surface of the sodium hydroxide forces the solution up into the jar. The level of dilute sodium hydroxide solution in the gas jar rises after the candle goes off.Īs the candle burns, it uses up the active part of air in the fixed amount of air enclosed in the gas jar. The candle burns for a while then it goes off.Īs the candle burns, it uses up the active part of air in the fixed amount of air enclosed. Remove the gas jar and measure the change in height. Measure and record the height of the air column once more. Mark on the gas jar the final level of the solution. After the candle has gone off leave the apparatus to cool to room temperature. Gently cover the burning candle with the gas jar. Measure the height of the air column and record it. Mark on the gas jar, the level of the solution. Place a small candle on a cork and float it on the solution. Put dilute sodium hydroxide solution in a trough. The active part of air can be determined experimentally using a burning candle as follows: The active part is oxygen, which forms about 20% of dry air by volume. The part of air that supports combustion is active air. (a) Burning of candle in airĬombustion or burning is a process in which a substance combines with oxygen with the production of heat. Several experiments such as burning of candle, heating of copper(II) oxide (combustion), smoldering of phosphorus and rusting, all of which use oxygen, can be done to determine the active part of air. Approximate percentage composition of air ComponentĮxperiments to determine the percentage of oxygen in air by volume. Composition of air Is air a mixture or a compound?Īir is a mixture of gases such as oxygen, nitrogen, carbon (IV) oxide and water vapour.Īir is considered a mixture and n ot a compound because the various components of air c an be separated by physical means (fractional distillation of liquefied air). Air is required for combustion of fuels to give energy. Living organisms need air for respiration.

State the applications of the reactivity series.Īir sustains life on earth.

State the pollution effects of combustion.

State the nature of the products of burning elements in air and in oxygen.

Experimentally compare the rates of combustion of elements in air and in oxygen.

Prepare and investigate the properties of oxygen.

State the methods of preventing rusting.

Investigate the conditions for rusting and state the composition of rust.

Describe fractional distillation of air.

Determine experimentally the percentage of oxygen in air by volume.

Past KCSE Questions on Air and Combustionīy the end of this lesson on Air and Combustion, the learner should be able to:

$obtained from liquid air by fractional distillation$

Obtained from liquid air by fractional distillation