Air and water Lesson Objectives • State the composition of clean, dry air • Describe the separation of oxygen and nitrogen from liquid air by fractional distillation • State the uses for nitrogen, oxygen and argon What is in air? Separating the gases from the air • Air gets separated because the gases in the mixture have different boiling points Fractional distillation of liquefied air 1. Air is filtered to remove dust 2. Air is cooled until it turns into liquid 3. Liquefied air is then passed into bottom of a fractionating column – the temperature of the column decreases upwards 4. There it is slowly warmed up. The gases boil off one by one and are collected at different heights Some uses of oxygen • In hospitals, patients with breathing problems are given oxygen through an oxygen mask, or in an oxygen tent. • Used in making steel • Used I gas cutting and welding • Used in diving and in space travel Some uses of nitrogen • Liquid nitrogen is very cold. (It boils at 2196 °C.) So it is used to quick-freeze food in food factories, and to freeze liquid in cracked pipes before repairing them. It is also used in hospitals to store tissue samples. • Nitrogen is unreactive. So it is flushed through food packaging to remove oxygen and keep the food fresh. Some uses of the noble gases • Argon provides the inert atmosphere in ordinary tungsten light bulbs. • Neon is used in advertising signs because it glows red when a current is passed through it. • Helium is used to fill balloons, since it is very light, and safe. In the next lesson.. • We’ll be discussing about the common pollutants in the air. • Try to refer the textbook for the pollutants in the air at home. (Self learning is important) • Thank you for your co-operation.
