Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Water Pollution: The contamination of water bodies such as lakes, rivers, and oceans by harmful substances like domestic sewage, industrial waste, and agricultural runoff ( and ).
Eutrophication: A process where water bodies receive excess nutrients (Nitrates and Phosphates), leading to excessive growth of algae (algal bloom), which depletes dissolved oxygen () and harms aquatic life.
Potable Water: Water that is safe for human consumption, being free from harmful germs, suspended impurities, and toxic chemicals.
Sedimentation and Loading: The process of allowing heavy suspended impurities to settle at the bottom. Alum, or Potash Alum (), is often added to speed up the settling of fine clay particles.
Filtration: Passing water through layers of sand and gravel to remove fine suspended particles that did not settle during sedimentation.
Chlorination: The process of adding chlorine () or bleaching powder () to water to kill harmful bacteria and microorganisms, making it safe to drink.
Aeration: Pumping air into filtered water to remove volatile gases like and , and to increase the level of dissolved oxygen (), which improves the taste of water.
Desalination: The process of removing dissolved salts (like and ) from seawater to make it suitable for drinking and irrigation.
📐Formulae
💡Examples
Problem 1:
Explain the role of Alum in the water purification process and provide its chemical formula.
Solution:
Alum, known chemically as Potash Alum (), acts as a 'loading agent' during sedimentation. It helps fine suspended clay particles clump together to form heavier particles that settle down quickly.
Explanation:
In large-scale water treatment, sedimentation by gravity alone is slow; adding alum increases the density of impurities via coagulation.
Problem 2:
Which chemical is used as a disinfectant in water treatment to kill pathogens? Write the chemical reaction if Chlorine gas is used.
Solution:
Chlorine () is used. When added to water, it reacts: . The Hypochlorous acid () produced is the active agent that kills germs.
Explanation:
Chlorination is the final stage of water treatment before distribution to ensure the water is biologically safe.
Problem 3:
Describe the effect of Nitrates () from fertilizers entering a pond.
Solution:
Nitrates act as nutrients for algae, causing an 'Algal Bloom'. When algae die, bacteria decompose them using up dissolved oxygen (). This results in high Biological Oxygen Demand () and causes fish to suffocate.
Explanation:
This process is called Eutrophication, a major consequence of agricultural water pollution.