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 Sources of Water Pollution  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. ​​Parameters Used to Determine Water Quality  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 indicates water is polluted. ​Hardness  ​Hard water produces less or no lather with soap. It is unsuitable for washing, drinking etc. Presence of hardness in water indicates pollution. ​Dissolved oxygen  ​It is responsible for support of aquatic life. Water present in streams, rivers contains high level of dissolved oxygen than that found in lakes, ponds etc. Water in a river or stream is considered polluted if the level of dissolved oxygen is less that what is found in normal water. It is measured using an instrument known as Oxygen Flow Meter. ​Biological Oxygen Demand  ​It is the amount of dissolved oxygen utilised by micro-organisms when oxidising organic matter. Polluted water has high level of biological oxygen demand. It is determined by comparing the amount of oxygen present in pure water and polluted water.​ Turbidity  It refers to the amount of suspended particulate matter in water. It measures the amount of light scattered by suspended solids in water. Greater the amount of suspended solids, greater is the scattering of light and hence water has high turbidity. Turbid water is incapable to support aquatic life. Solids that cause turbidity in water are: Clay Insoluble waste substances Microorganisms Ways to Control Water Pollution  Proper treatment of sewage before its discharge in water bodies. Neutralization of chemicals released from factories. Gravity settlement and screening processes helps in removal of heavy floating solids. Oxidation of organic matter for its removal. Destruction of pathogens by ultraviolet radiations.

International Standards for Drinking Water

Fluoride

Concentration upto 1 ppm − Useful and recommended as it makes enamel of teeth hard by converting hydroxyapatite into fluorapatite Concentration above 2 ppm − Causes brown mottling of teeth Concentration over 10 ppm − Harmful effects on bone and teeth

Lead

It is a water pollutant. Should not exceed beyond 50 ppb Can damage kidney, liver, and reproductive system

Sulphate

Moderate − Harmless Excessive − Laxative effect

Nitrate

Maximum limit − 50 ppm Excess nitrate causes ‘Blue Baby Syndrome’. 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 Sources of Water Pollution  Household deterge…