AIR

AIR

The atmosphere surrounding the earth contains air. Air is a mixture of gases. It consists of 78% nitrogen, 21% oxygen , argon and other inert gases to the extent of about 1.0%. In addition carbon(iv)oxide is another important constituent of the atmosphere which varies in amount from 0.1% to 0.3%. The variation is mainly due to combustion photosynthetic processes. The other gases e.g sulphur (iv) oxide, ozone etc are found in very small quantities. Water vapour is also an important constituent which varies from region to region.

Reasons why air is a mixture

1.       The properties of the constituents of air are not change.

2.       The proportion of the constituents of air vary from place to place.

3.       No thermal change occurs when the constituent of the air are mixed together.

4.       Liquid air does not have a fixed boiling point.

5.       On distillation of liquefied air, nitrogen distilled off first, leaving behind oxygen in the liquid form.

PROPERTIES OF AIR

  I.            Air has weight.

II.            Air is under pressure

III.            It has temperature

IV.            It usually contains some water vapour

V.            It has some velocity (speed)

FLAMES

Flames are produced when substances burn. A flame can be described as a region where gases combine chemically, with the production of heat and light. In most cases, one of the gases involves is the oxygen although combustion can occur without oxygen, for example when hydrogen burns in chlorine.

Flames are not homogenous, but are composed of several defined zones. These type of flame produce  depends on the nature of the substance burning. A flame may be luminous or non-luminous. The luminosity of a flame is caused by the presence of solid particles in the flame. An increase in the temperature or pressure of the burning gases also increase the luminosity of a flame.

HYDROGEN  FLAME: Hydrogen burns with a very faint , non -luminous flame . The structure of the hydrogen flame is simple, consisting of only two region: the unburnt gas zone and the zone of the complete combustion.

CANDLE FLAME: A candle burns with a luminous flame. Four zones can be identified  in the flame:

   i.            The zone of unburn gas around the wick

 ii.            The bright  yellow luminous zone where there is incomplete burning of the hydrocarbon due to insufficient air supply.

iii.            The barely visible, non-luminous zone on the outsider where complete combustion of carbon particles takes place because of a plentiful supply of air from the atmosphere.

iv.            The blue zone at the base of the flame which is also a region of complete combustion.

BUNSEN FLAME: A Bunsen burner is built with an air inlet at the base of the burner tube so that a stream of air can be supplied to the flame together with the fuel gas. This supplement the external supply of air , and allows a more complete combustion of the fuel. The air-hole can also be adjusted to give a flame with the required luminosity.

The fuel for the Bunsen burner is a mixture of hydrocarbon gases (methane and butane) and some hydrogen and carbon (ii) oxide. The products of combustion are mainly water, carbon (iv) oxide, carbon (ii) oxide and soot.

To produce luminous Bunsen flame, the airhole at the base of the burner tube should be closed. The flame produced is highly and wavy, with a large, bright yellow zone within it. It is not hot, and deposits soot on the surface of any object held in it. Like the candle flame, it has four zones.

To produce a non-luminous Bunsen flame, the air hole should be kept open. The flame is non-luminous, much hotter, cleaner and more compact than the luminous Bunsen flame. Only three (3) zones can be seen in the flame:

1.       The unburnt gas zone, much reduce in size when compare to that of the luminous Bunsen flame.

2.       The luminous zone also much smaller.

3.       The outermost non-luminous zone which was increased in size because the flame has a sufficient

  

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