Air and Water

Tests for Water#

Purification of Water#

• Water is pumped into screens, which remove solid floating debris.

• Aluminum sulfate is added to coagulate (stick together) small pieces of clay so that they are easily removed.

• The water is then filtered through coarse sand to remove larger, insoluble debris.

• The water encounters more flocculants (chemicals that make particles move down to bottom of tank) and is filtered again through fine sand.

• Chlorine gas is bubbled through the water to kill bacteria. This makes the water slightly acidic, so to reverse this appropriate amounts of sodium hydroxide (an alkali) is added.

• Some countries also add fluorine

Use of Water#

Air#

• Clean air is composed of approximately

  • 79% nitrogen

  • 20% oxygen

  • Remainder: noble gases, water vapor & carbon dioxide

Pollutants in Air#

Fractional Distillation of Air#

• Air is filtered to remove dust

• Water vapor and carbon dioxide removed, (because they would freeze and block the pipes):

  • air is cooled until water vapor condenses

  • then passes over absorbent beads to trap carbon dioxide

• It is compressed, causing it to heat up. Cooled by recycling cold air

• The cold compressed air is passed through a jet, into a larger space. It expands rapidly, making it very cold.

• This is repeated, cooling the air more. By -200°C it is liquid except for neon and helium. These gases are removed. They can be separated from each other by absorption on charcoal.

• The liquid air is pumped into the fractioning column. There it is slowly warmed up. The gases boil off one by one, and are collected in tanks or cylinders.

• Sources of methane: oil and natural gas, decomposition of vegetation, and waste gases from digestion in animals

Catalytic Convertor#

• In the combustion engine, insufficient amounts of oxygen lead to incomplete combustion of the carbon containing fuel

• Gases produced: (a) carbon monoxide (b) oxides of nitrogen

• A catalytic convertor catalyzes the reduction of NO~2~ to nitrogen gas N~2~ and catalyzes the oxidation of CO to CO~2~

Rust Preventition#

• Coating with something to prevent contact with air and moisture

  • Plastic, paint and grease

  • Electroplating with tin or chromium

  • Galvanising: dipping in molten zinc

• Sacrificial protection: attaching a piece of metal that is more reactive that iron to object, commonly magnesium or zinc. This will corrode in the place of iron.

Fertilizer#

• NPK used in fertilizers because:

  • Nitrogen is needed for chlorophyll and other proteins.

  • Phosphorus helps roots grow and crops ripen.

  • Potassium helps make proteins and resist diseases.

• All alkalis (except ammonia) will react with ammonium compounds, removing ammonia, for example:

Calcium hydroxide+Ammonium chloride→Calcium Chloride+Water+Ammonia

Greenhouse Gases#

• The greenhouse gases are: carbon dioxide and methane.

• They stop heat escaping in to space.

• Too much greenhouse gases leads to climate change.

• This will cause the ice poles to melt, rising sea levels, more droughts, storms, floods and famine; global warming

Formation of Carbon Dioxide#

• Carbon dioxide is produced whenever carbon or any of its compound are completely burned in excess oxygen

• It is also formed as a product of respiration

• It is produced as product of reaction between an acid and carbon

• From the thermal decomposition of a carbonate

Haber Process#

• Industrial manufacture of ammonia NH~3~

N~2~ (g) + 3H~2~ (g) ⇌⇌ 2NH~3~ (g)

• Raw materials:

  • Nitrogen: from the air

  • Hydrogen: methane + steam → carbon dioxide + hydrogen

• Essential conditions:

  • Temperature: 450°C

  • Pressure: 200atm

  • Catalyst: Iron

Carbon Cycle#