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9. (a) What property of water makes it very useful in the human body as a medium in which chemical reactions occur, and also allows it to become polluted or contaminated very easily in other situations? (5) The treatment of a water supply for domestic use may involve several stages - Leaving Cert Chemistry - Question 9 - 2002
Question 9
9. (a) What property of water makes it very useful in the human body as a medium in which chemical reactions occur, and also allows it to become polluted or contamin... show full transcript
Worked Solution & Example Answer:9. (a) What property of water makes it very useful in the human body as a medium in which chemical reactions occur, and also allows it to become polluted or contaminated very easily in other situations? (5) The treatment of a water supply for domestic use may involve several stages - Leaving Cert Chemistry - Question 9 - 2002
Step 1
What property of water makes it very useful in the human body as a medium in which chemical reactions occur, and also allows it to become polluted or contaminated very easily in other situations?
Answer
The key property of water that makes it instrumental in the human body is its effectiveness as a good solvent. Water's polarity allows it to dissolve various substances, facilitating essential biochemical reactions. This polarity also leads to the formation of dipole-dipole hydrogen bonds, which contribute to the stability of structures such as proteins and nucleic acids. However, due to this polarity, water can easily attract other molecules, making it susceptible to contamination from various pollutants and chemicals.
Step 2
Describe what happens at each of these three stages.
Answer
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Sedimentation: In this initial stage, suspended solids in the water settle down due to gravity. Larger particles, such as sand and silt, sink to the bottom of the sedimentation tank, allowing clearer water to flow to the next treatment stage. This process helps remove a significant amount of particulate matter.
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Flocculation: During flocculation, chemicals are added to the water to promote the agglomeration of smaller particles into larger flocs. These flocs can then be removed more easily during the following treatment steps. This process enhances the efficiency of sedimentation and helps reduce the turbidity of the water.
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Filtration: Filtration involves passing water through various porous materials, such as sand, gravel, or activated carbon, to remove remaining suspended solids and impurities. The filtered water is then much cleaner and safer for further treatment or distribution.
Step 3
Identify one other stage in water treatment which involves the addition of a chemical to the water. Name one chemical added during this stage and state why this chemical is added.
Answer
Another stage in water treatment that involves adding a chemical is chlorination. Chlorine is added to kill harmful microorganisms present in the water, thus disinfecting it and preventing diseases. This step is crucial in ensuring the microbiological safety of drinking water.
Step 4
Distinguish between the primary and secondary stages of sewage treatment.
Answer
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Primary Treatment: This stage focuses on the physical removal of large solids from sewage. Through processes like screening and settling, large debris, such as plastics and organic matter, are physically removed. This stage primarily acts as a preliminary filtration method to reduce the load on subsequent treatments.
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Secondary Treatment: Here, biological processes are utilized to degrade dissolved organic matter. Microorganisms consume the organic pollutants in the sewage, breaking them down into simpler compounds. This stage effectively reduces biochemical oxygen demand (BOD) and helps in maintaining environmental standards.
Step 5
What is the purpose of tertiary treatment?
Answer
The purpose of tertiary treatment is to further enhance the quality of treated wastewater, often referred to as effluent. This stage removes remaining contaminants, nutrients like nitrogen and phosphorus, and pathogens that may still be present after secondary treatment. Tertiary treatment ensures that the water is suitable for discharge into natural water bodies or for reuse in irrigation, industrial processes, or even as drinking water, contributing to water conservation and pollution prevention.