Chemistry 12: Water (PDF)

## 12.1 Water ### 12.1.1 Water As Solvent Water is very good at dissolving substances. For this reason, natural water such as rainwater and groundwater is not pure water. As water falls through the atmosphere, it dissolves a little oxygen, nitrogen, carbon dioxide, and dust particles. During thund...

## 12.1 Water ### 12.1.1 Water As Solvent Water is very good at dissolving substances. For this reason, natural water such as rainwater and groundwater is not pure water. As water falls through the atmosphere, it dissolves a little oxygen, nitrogen, carbon dioxide, and dust particles. During thunder storms, it also dissolves nitric acid. Ground water dissolves minerals from rocks and soils as it moves along on or beneath Earth's surface. Ground water also dissolves many substances from decaying plants and animals. ### 12.1.2 Quality of Water From Natural Resources Water from natural resources such as lakes, streams, and underground rivers can contain many dissolved substances that can be beneficial or harmful. ### 12.1.3 Disadvantages of Natural Substances Found in Water 1. Dissolved oxygen: Where do fish and other marine life get their oxygen? Water contains dissolved oxygen. This oxygen is responsible for the survival of aquatic organisms. 2. Metal compounds: Natural water can contain metals such as iron, sodium, potassium, magnesium, calcium, manganese, zinc and copper. Some of these metals are necessary for biological processes, their excessive concentration can be poisonous for aquatic organisms and humans. 3. Plastics: Plastic waste can pollute water bodies. This is a serious threat to aquatic life and ecosystem. 4. Wastewater: Wastewater can enter natural water supplies. Wastewater carries pathogens, bacteria, viruses and other harmful substances. These pollutants pose a serious threat to humans and aquatic life. 5. Harmful Microbes: Natural water sources can contain harmful microbes such as bacteria, viruses and parasites that can cause waterborne diseases such as diarrhea, dysentery, cholera and stomach upsets. 6. Nitrates from fertilizers: Fertilizers add nitrates to water bodies through agricultural runoff. High concentrations of nitrates in drinking water cause health risks, especially for young children. 7. Phosphates from fertilizers and detergents: Phosphates in fertilizers and detergents can enter water bodies through runoff. High concentrations of phosphate can cause eutrophication. This can cause harmful algae blooms and oxygen caps in water bodies. Detergents used in water systems can destroy the outer mucous membranes that protect fish from bacteria and parasites. In addition, detergents can also damage their gills. ### 12.1.4 Benefits of Natural Substances Found in Water 1. Dissolved oxygen: Existence of aquatic life depends on dissolved oxygen. This oxygen supports the respiration process of aquatic organisms. 2. Essential minerals: Metal compounds in natural water can provide essential minerals needed for various biological processes. For example, iron is necessary for the production of hemoglobin in the blood, which carries oxygen to the cells of our body. Metals like zinc, copper, and manganese activate enzyme activity the proper functioning of biological systems. ## 12.2 Treatment of Domestic Water Supply The treatment of domestic water supply involves several processes to ensure that water is safe for human use. ### Raw Water Treatment Raw water is treated in a municipal water purification plant, to make it fit for drinking and domestic purposes. Various stages in this treatment are: 1. **Sedimentation**: It is the process in which water is allowed to stand in a reservoir. The suspended matter sinks to the bottom. 2. **Coagulation**: It is the process in which water is treated with slaked lime and alum. These materials react to form a gelatinous mass of aluminum hydroxide $3Ca(OH)_2(aq) + Al_2(SO_4)_3(aq) \longrightarrow 2Al(OH)_3(s) + 3CaSO_4(aq)$ ## 12.2.1 Distilled Water Water purified by distillation is called distilled water. The process of distillation involves heating water to boiling point, collecting the vapors, and condensing it back into the liquid. The important aspect behind. Distilled water is free of any contaminants. The electrical conductivity of distilled water is very low. The pH of distilled water is 7. ### Uses in Chemistry: 1. Distilled water is usually used in laboratories to prepare chemical reagents and solutions 2. Distilled water is used in the calibration of various analytical instruments, e.g., pH meter. ## 12.2.2 Tap Water Water supplied through the municipal water system to households and for commercial purposes is called tap water. It comes from lakes, reservoirs, and groundwater. It undergoes various processes to meet safety standards to make it safe for people. ### Applications in Chemistry Laboratory 1. Tap water is used as a solvent for general purposes, such as cleaning glassware, equipment, etc 2. It is also used for educational and simple demonstration as a readily available solvent. ## 12.3 Water Pollution Water is very good at dissolving substances. As water rain or snow flows over land and through soil, it dissolves minerals. The freshwater, we drink use for our daily life is no more a dilute solution containing a number of minerals when many human activities pollute the concentration, water becomes unfit for human use. Many human activities pollute the surface and groundwater. Human activities such as household waste, agricultural waste, livestock waste, pesticides, oil leaks, detergents, septic tanks, petroleum, and natural gas production may result in contamination of water bodies. We will discuss household waste and industrial waste in this unit. You will learn about other types of waste in higher grades. ### Household Wastes Household wastes include human wastes, livestock wastes, soaps and detergents, paints and oil, food, vegetable wastes, garbage, etc. Although detergents have stronger cleansing action than soap, they remain in the water for a long time and make water unfit for aquatic life. When household water containing detergents is discharged into lakes, ponds, rivers, etc. it causes the death of aquatic life. Chemical and bacterial contents in household water can contaminate surface and underground water. Bacterial contents present in water may cause infectious diseases such as cholera, jaundice, hepatitis, typhoid, dysentery, etc. ### Society, Technology and Science Water treatment is essential for many reasons: * Through water purification, we can avoid drinking impure and contaminated water, which causes many epidemic diseases and unsafe for healthy life. * It removes bacteria, viruses and parasites which may cause diarrhoea, dysentery, botulism, typhoid, cholera, polio, and hepatitis. * It also removes heavy metals like, As, Cr and Pb which can cause long term neurological problems, kidney diseases, nausea, dizziness, and cancer. * It also improves the flavor and appearance. ## 12.4 Waterborne Diseases Human wastes are dumped on the ground or into the nearest stream. Human waste contains infectious microorganisms, which spread diseases like typhoid fever, dysentery, and hepatitis. Chemical and bacterial contents in livestock waste can pollute surface and groundwater causing the above-mentioned diseases. Hepatitis a viral disease occasionally spreads through drinking Water. Unclean water supplies, poor sanitation, and poor hygiene kill 2,668,000 people worldwide each year. Water in swimming pools is purified from pathogenic organisms by aeration and chlorination. ### Some waterborne diseases are given below: * **Dysentery**: Dysentery is also an intestinal disease. It is caused by a parasite, entamoeba. This infection is transmitted by fecal contamination of water or food by the encysted organism. Patients have mild to severe abdominal cramps, diarrhea, chocolate-colored stool with mucous and sometimes blood. * **Jaundice**: This disease proceeds from obstruction of the liver. Excess of bile from the liver enters the blood and causes yellowness of skin and eyes. It leads to loss of appetite, weakness, and fatigue. * **Hepatitis**: Hepatitis is an acute inflammation of the liver. It is caused by viruses and is classified as Hepatitis A, B, C, D, and E. Hepatitis A and E spread through polluted water. * **Typhoid**: Typhoid is a dangerous intestinal disease. It spreads by polluted water containing bacteria such as salmonella typhi, salmonella paratyphi, and salmonella enteritidis. It is characterized by continuous fever between 101°F to 104°F and irregular pulse. ## 12.5 Ways to Deal With The Negative Effects of Water Pollution Water pollution affects life in many ways. Here are some ways to deal with them are as follows: 1. Some pollutants reduce oxygen levels in water bodies and make the survival of aquatic life difficult. To prevent this, it is important to control nutrient flow and properly treat sewage and industrial waste that encourage excessive algae growth. 2. Heavy metals present in polluted water, can accumulate in the tissues of aquatic organisms. These metals also harm human health if people consume them as food. 3. Preventing industrial wastewater from entering waterways can minimize emissions of such pollutants. Water-borne diseases like hepatitis, cholera, dysentery, etc. are caused by harmful microbes. Ensuring proper treatment of domestic and industrial wastewater, compliance with good sanitary and hygiene requirements, and providing access to clean drinking water are crucial in preventing water-borne diseases. ## 12.6 Water Scarcity in Pakistan Water scarcity is a major problem in Pakistan. This is mainly due to the following factors: 1. **Population Growth**: The population of Pakistan is growing rapidly, which increases the demand for water in agriculture, industry, and homes. 2. **Climate Change**: Climate change has caused irregular rainfall patterns, which affects water availability. The country's water resources are also declining due to excessive extraction of water from groundwater aquifers and insufficient irrigation practices. 3. **Inadequate water supply**: Traditional flood irrigation methods are widely used in Pakistan. This has resulted in significant water losses through evaporation and inadequate water distribution. To solve the problem of water scarcity in Pakistan, the following are necessary: * Effective water management practices. * Development of infrastructure. * Policy reforms. * Public awareness of responsible water use and its promotion. * Strict regulations and monitoring systems to control groundwater and prevent illegal drilling are essential. ## 12.7 Fertilizers Fertilizers are substances that provide essential elements for plant growth. These elements are essential to enhance crop yields. Fertilizers mainly provide three main nutrients, nitrogen (N), phosphorus (P), and potassium (K), hence known as NPK fertilizers. Urea, potassium nitrate, and ammonium salts such as di-ammonium phosphate (superphosphate) are important fertilizers. Fertilizers dissolve in water. So they provide nutrients to the plants in a readily available form. It is important to give fertilizers at the right time and in the right amount. This practice is called nutrient management. It optimizes the intake of nutrients by plants and reduces the loss of nutrients. This practice can minimize environmental problems such as nutrient runoff into water bodies. ### Key Points: * Hepatitis a viral disease occasionally spreads through drinking polluted water. * Unclean water supplies, poor sanitation and poor hygiene kill 2,668,000 people worldwide each year. * Anhydrous copper(ll) sulphate is used to detect water, on absorbing water it turns blue. * Water from natural resources contains useful and harmful substances. * Nitrates and phosphates present in water damage aquatic life. * Sewage contains harmful microbes which cause diseases. * Sedementation, filteration, and chlorination are major steps in the treatment of domestic water supply. * Urea, ammonium salts, and nitrates are used as fertilizers.