13.2    Environmental Consequence of Using Nitrogen Compounds

Excessive use of nitrate fertilisers

• When excessive nitrate or ammonium fertilisers are used, the unabsorbed ones will dissolve in rain water and it leaches into lakes and rivers
• An excess of these chemicals in the waters can promote the growth of    algae, eventually causing an algae bloom. The algae grow exponentially across the surface of water, blocking sunlight from the reach of aquatic plants and causes the plants to die
• The algae grow faster than being consumed, eventually a large number of algae die without being consumed. When their remains decompose, the process takes up a lot of oxygen from the water. The oxygen level in the water will eventually reach a level where no life can sustain.
• This process of excess growth leading to the destruction of life in the water is known as eutrophication.
• Since nitrates are soluble in water, removing them from drinking water is very expensive. High levels of nitrates in drinking water can cause a disease in young babies called ‘blue baby syndrome’. Nitrates in water can also potentially cause  stomach  cancer.

Oxides of  nitrogen as pollutants

• i. Nitrogen monoxide, NO is formed when electric spark is passed through a medium of nitrogen and oxygen.ii. This happens in the atmosphere during lightning storms. In petrol engines, it is formed when sparks are used to ignite the petrol
  N2(g) + O2(g) → 2NO(g)

  iii. It can be removed in petrol engines using a catalytic converter. A catalytic converter uses expensive metals like platinum as a catalyst to convert harmful pollutants into non-harmful substances. In this case, it converts the harmful nitrogen monoxide and carbon monoxide into non-harmful nitrogen and carbon dioxide gases
  2NO(g) + 2CO(g) → N2(g) + CO2(g)

• • Nitrogen monoxide is converted to nitrogen dioxide, NO2 in the atmosphere.
    2NO(g) + O2(g) → 2NO2(g)
  • Nitrogen dioxide acts as a catalyst in the conversion of sulfur dioxide, SO2 into sulfur trioxide, SO3.
    SO2(g) + NO2(g) → SO3(g) + NO(g)
  • Sulfur dioxide and sulfur trioxide are the main causes of acid rain. Sulfur dioxide oxidises into sulfur trioxide and sulfur trioxide reacts with water in the atmosphere to form sulfuric acid
    SO3(g) + H2O(l) → H2SO4(aq)
  • The sulfuric acid then fall on earth as acid rain.
  • The nitrogen monoxide reacts with water in the atmosphere to re-form nitrogen dioxide and the cycle repeats
    2NO(g) + O2(g) → 2NO2(g)