Chemistry Kenya
Air and Combustion
Air and Combustion
Air and Combustion
Composition of air
Approximate percentage of Nitrogen and oxygen in air by volume(mention of carbon dioxide and noble gases as other constituents of air)
The composition of air is not exactly the same everywhere. It changes slightly from day to day and from place to place. There is more water vapour in the air on a damp day and in air above water bodies such as oceans, seas, lakes, rivers, etc. Over busy cities and industrial areas there is more carbon dioxide. But the uneven heating of the earth's surface by the sun causes the air to move continually, resulting in winds. The resultant winds spread the pollutants around.
The Presence of Different Gases in Air
The determination of air by mass was carried out by Dumas in 1841. The apparatus used consists of three units as shown below.
- Several U-tubes containing potassium hydroxide pellets to remove carbon dioxide (only one tube shown in the figure for simplicity).
- Another set of U-tubes containing concentrated sulphuric acid to remove water vapour (only one tube shown in the figure).
- A heated, weighed glass tube containing finely divided copper to absorb oxygen.
The three parts of the apparatus would, therefore, remove all carbon dioxide, water vapour and oxygen contained in air. The remaining gas which enters the weighed evacuated flask (globe) will be atmospheric nitrogen and, of course, plus the rare gases. The copper will have reacted with all oxygen to form copper (II) oxide. The increase in mass of the copper will give the mass of oxygen. The increase in weight of the globe will be due to the weight of nitrogen and the rare gases. If we neglect the weight of carbon dioxide, the percentage of oxygen by mass (weight) in dry, pure air is 23.2% and the remaining 76.8% is the percentage of nitrogen and rare gases.
Quantitative determinative of oxygen in air using copper, iron findings and burning candle
Burning of substances in air; carbon, sulphur, phosphorus (CARE) sodium and copper
Oxygen as an active part of air (mass changes involved)
Fractional distillation of liquefied air
Rusting: conditions, composition and prevention
Oxygen Introduction
Laboratory preparation of oxygen using 20 volume by volume (v/v) hydrogen peroxide with manganese (IV) oxide or reaction of sodium peroxide with water (relate methods of collection to the properties of the gas)
Properties of oxygen; physical and chemical
Combustion of elements in oxygen (metals and non-metals)
Competition of combined oxygen illustrated by the reaction of magnesium with carbon (IV) oxide, lead (II) oxide and copper (II) oxide
Atmospheric pollution due to burning in oxygen
Reactivity Series
Order of reactivity of elements from reaction with oxygen: potassium, sodium, calcium, magnesium, aluminium, carbon, zinc, iron, lead and copper. (It is not possible to establish full series practically)
Uses: oxy-acetylene in welding; life support functions
Applications: Extraction of metals (use the concept of reactivity series only)
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