Practical Work

Detection of Some Gases

Water Pollution 

• Introduction of unwanted substances to the water bodies that affects the natural quality of water decreasing its usability
• Ways to identify polluted water:
  • Foul smell
  • Bad taste
  • Oil or grease floating on the surface
  • Excessive algal growth
  • Growth of weeds

• Household detergents
• Sewage
• Domestic and industrial waste
• Oil spills
• Thermal pollution

Causes of Water Pollution

• Pathogens − Enter water from sewage and animal excreta

E.Coli and S.faecalis cause gastrointestinal diseases.

• Organic wastes − Leaves, grass trash, etc. reach water with run off.

  • Oxygen dissolved in water is called dissolved oxygen (DO). DO in water (10 ppm) is very less as compared to air (200,000 ppm).
  • For decomposition of organic matter, oxygen is required by bacteria. Therefore, presence of organic matter in water depletes the DO of water.
  • If DO reaches less than 6 ppm, then the growth of fish gets inhibited.
  • If there is deficiency of oxygen in water, then anaerobic bacteria start degrading the organic matter, resulting in foul small and harmful effects on human health.
  • Biochemical Oxygen Demand (BOD) − Amount of oxygen required by bacteria to break down organic matter present in water.
  • Therefore, BOD represents the amount of organic matter present in water.
  • Less polluted water has lower BOD value and vice-versa.

• Chemical pollutants

  • Heavy metals dissolved in water are harmful as our body cannot excrete them. These metals cause damage to kidneys, CNS, liver, when accumulated beyond tolerance limit in body.
  • Acids and raw salts (used to melt ice) also act as water pollutants.
  • Organic chemicals such as petroleum products (from oil spills), pesticides, industrial chemicals such as PCBs, detergents also fall under category of chemical water pollutants.
  • Fertilizers also cause water pollution. These fertilizers contain phosphates, which enhance algae growth (algae bloom). Algae consume a major part of dissolved oxygen, thus depriving aquatic plants and animals of it, hence killing them. This condition is called Eutrophication.

• pH value
  • ​Presence of pollutants alters the natural pH (7) of water.
  • This causes harm to aquatic plants and animals
  • pH value less than 7 indicates water is acidic.
  • pH value greater than 7 indicates water is basic.
• ​Bacteria 
  • ​Presence of bacteria can be detected by observing samples of water from a source under microscope at regular intervals.
  • Presence of bacteria in water indi…