Environmental Chemistry - II (Class XI)

It is a highly dangerous gas with a high potential of causing cancer and respiratory ailments.

A chlorofluorocarbon (CFC) is an organic compound that contains only carbon, chlorine, and fluorine, produced as volatile derivative of methane, ethane, and propane. They are also commonly known by the DuPont brand name Freon. The most common representative is dichlorodifluoromethane (R-12 or Freon-12).

Photochemical smog is mainly composed of ozone, nitrogen dioxide and volatile organic compounds. Sulphur dioxide is not a component of photochemical smog.

The brown haze of photochemical smog is largely attributed to NO₂.

The toxic effects of carbon monoxide on human beings and animals arise from its reversible combination with haemoglobin (Hb) in red blood cells, which cause displacement of oxygen. This results in oxygen starvation or anoxia. The maximum permissible concentration of CO in the atmosphere is 40 ppm for an exposure of 8 hours. A higher concentration of CO or a longer exposure starts causing adverse effects. In small amounts, CO causes headaches and fatigue, and in larger doses, it can be lethal.

The products of photochemical smog are peroxyacetyl nitrate and ozone. 

Detergents and fertilisers containing phosphate anion are mainly responsible for eutrophication.

Chlorine gas was used earlier for bleaching paper. It is being replaced by hydrogen peroxide with suitable catalyst.

Inhaling of nitrogen oxides by humans results in pulmonary edema and hemorrhage. Several sensitive plants get adversely affected by NOx even at the concentration of 1 ppm for a day or 0.35 ppm for a few months. The affected plants start shedding their leaves and fruit. Nitrogen oxides cause fading of textile dyes and deterioration of cotton and nylon fabrics.

A considerable part of the harmful U.V. radition of the sun does not reach the surface of the earth because above earth’s atmosphere, there is a layer of ozone.

Exposure to SO₂ causes deterioration of fabrics (cotton, rayon), paper and leather. Being corrosive, it has damaging effects on metals, such as iron, steel, aluminium, and on building materials, such as limestone, marble, roof slate, etc. Marble structures, limestone and geological sources of ammonia act as a sink for atmospheric SO₂.

All of the above are the achievements of green chemistry.

Carbon monoxide binds to hemoglobin in red blood cells to form carboxyhaemoglobin, which is extremely stable (200+ times stronger bond than oxyhemoglobin). This prevents oxygen transport, causing CO poisoning. CO does not form nitro-haemoglobin, carbon dioxide haemoglobin, or oxy-haemoglobin.

The elements or organisms that can consume a pollutant are known as 'sinks'. Recent researches have shown that soil is capable of removing large amounts of CO from the atmosphere by the action of some soil microorganisms. The microorganisms act as a sink for CO.

The pH of rainwater due to the presence of H⁺ ions formed by the reaction of rainwater with CO₂ present in atmosphere will be ~ 5.6.