Page 17 - Curriculum Visions Dynamic Book

Industrial preparation of oxygen
The easiest way to obtain oxygen in large quantities is to liquefy air in bulk. This process is called distillation, and it is a very low temperature version of, for example, how oil and other mixtures are obtained. The process takes place in a tall column (called a fractionation column) made of a set of “leaky trays”. Air is cooled until it becomes liquid and is then poured onto the trays. There is a boiler at the bottom and a condenser (a trap for the gas given off) at the top.
In this gas, the air begins to evaporate and nitrogen is given off as a gas, while the oxygen (which goes into a gas less easily than nitrogen – it is less volatile) drips to the bottom. In this way carefully controlled conditions can separate out the oxygen from other gases.
The liquid air is kept under a pressure of five atmospheres in the tower, at which pressure the boiling point of the nitrogen and oxygen are much higher (and so easier to maintain) than at normal atmospheric pressure.
catalyst: a substance that speeds up a chemical reaction but itself remains unaltered at the end of the reaction.
decompose: to break down a substance (for example by heat or with the aid of a catalyst) into simpler components. In such a chemical reaction only one substance is involved.
 Fractional distillation of air. The liquid air is pumped into a fractionating column and subjected to pressure and temperature changes to separate the component gases that make up air.
Air is cooled
to -190°C and pressurised to generate liquid air.
Nitrogen gas. Nitrogen boils at -196°C. It is used to make fertilisers, and nitric acid.
Argon gas. Argon boils at -186°C and is used as an unreactive filling for some light bulbs.
Liquid oxygen. Oxygen boils at -183°C and is used for breathing apparatus.
EQUATION 1: Production of oxygen using hydrogen peroxide
Hydrogen peroxide ➪ oxygen + water 2H2O2(aq) ➪ O2(g) + 2H2O(l)
Also...
catalyst
Hydrogen Oxygen
➡+
EQUATION 2: Using potassium chlorate to make oxygen
Potassium chlorate ➪ potassium chloride + oxygen
Manganese oxide acts as a catalyst, a compound that is essential to allow a reaction to happen quickly, but that actually does not change chemically itself.
The decomposition of potassium chlorate (KClO3) occurs when the temperature reaches 400°C, but with the use of the catalyst manganese dioxide (MnO2) decomposition occurs
at a temperature of only 200°C. Hydrogen peroxide decomposes with no heating at all as shown in the demonstration on this page.
There are many other examples of catalysts. One of the most common examples is the catalytic converter found in the exhaust systems of modern cars.
2KClO (s) ➪ 2KCl(s) 3
+
3O (g) 2
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