Prepare effectively with solved exercises on water, designed for PTB curriculum. Cover essential topics like water properties, treatment processes, and industrial applications to boost your understanding and exam readiness.
Short Questions (Extended Answers)
- How water rises in plants?
Water rises in plants through a combination of capillary action, root pressure, and transpiration. Capillary action is the movement of water within the narrow xylem vessels due to adhesion (attraction between water and vessel walls) and cohesion (attraction between water molecules). Transpiration from the leaves creates a negative pressure that pulls water upward from the roots. - Which forces are responsible for dissolving polar substances in water?
Polar substances dissolve in water mainly due to hydrogen bonding and dipole-dipole interactions. Water, being a polar molecule, has a partial positive charge on hydrogen and a partial negative charge on oxygen. This allows it to surround and interact with other polar molecules or ions, stabilizing them in solution. - Why are non-polar compounds insoluble in water?
Non-polar compounds do not dissolve in water because they lack polar groups that can form hydrogen bonds with water. Water molecules are more attracted to each other than to non-polar molecules, resulting in the separation of water and non-polar substances, such as oils. - How does water dissolve sugar and alcohol?
Water dissolves sugar and alcohol through hydrogen bonding. Both sugar and alcohol have hydroxyl (OH) groups, which can form hydrogen bonds with water molecules, allowing them to dissolve readily in water. - How does limestone dissolve in water?
Limestone, primarily composed of calcium carbonate (CaCO3), dissolves in water containing dissolved carbon dioxide (CO2). The CO2 reacts with water to form carbonic acid (H2CO3), which further reacts with calcium carbonate to form soluble calcium bicarbonate [Ca(HCO3)2]. - Differentiate between soft and hard water.
Soft water contains little to no dissolved minerals like calcium and magnesium. In contrast, hard water has high concentrations of these minerals, which can cause scaling in pipes and reduce the effectiveness of soaps and detergents. - What are the causes of hardness in water?
Hardness is caused by the presence of dissolved calcium and magnesium ions, which originate from the weathering of rocks and minerals, such as limestone and dolomite. - What are the effects of temporary hardness in water?
Temporary hardness, caused by dissolved bicarbonate minerals, can lead to scale formation in kettles and boilers when heated. This hardness can be removed by boiling the water. - Mention the disadvantages of detergents.
Detergents contain synthetic chemicals that can harm aquatic life when they enter water bodies. They can reduce the surface tension of water, making it difficult for organisms to breathe, and may also accumulate in the environment, leading to toxic effects. - What is the difference between biodegradable and non-biodegradable substances?
Biodegradable substances can decompose naturally by the action of microorganisms, while non-biodegradable substances, such as plastics, persist in the environment and do not break down easily. - How detergents make the water unfit for aquatic life?
Detergents contain phosphates and other chemicals that can lead to eutrophication, where excessive nutrients cause algal blooms. These blooms deplete oxygen in the water, making it difficult for aquatic life to survive. - Why are pesticides used?
Pesticides are chemicals used to eliminate pests that damage crops, spread diseases, or harm livestock. They help in increasing agricultural productivity and protecting stored products. - What are the reasons for waterborne diseases?
Waterborne diseases are caused by the ingestion of water contaminated with pathogenic microorganisms, such as bacteria, viruses, and parasites. Common sources of contamination include sewage, agricultural runoff, and improper sanitation. - How can waterborne diseases be prevented?
Preventive measures include purifying drinking water through filtration, chlorination, or boiling; practicing good hygiene, such as washing hands regularly; and improving sanitation and waste management.
Extensive Questions (Detailed Answers)
- How does the polarity of a water molecule play its role in dissolving substances?
The polarity of water means that it has a partial positive charge on one side (near the hydrogen atoms) and a partial negative charge on the other (near the oxygen atom). This allows water to interact with other polar molecules or ions. When an ionic compound, such as salt (NaCl), is added to water, the negative ends of the water molecules are attracted to the positive sodium ions, and the positive ends are attracted to the negative chloride ions. This attraction causes the ions to separate and become surrounded by water molecules, dissolving the salt. Similarly, polar covalent compounds, such as sugar, dissolve because their polar regions can form hydrogen bonds with water. - Explain the methods of removing permanent hardness.
Permanent hardness is caused by the presence of dissolved calcium and magnesium salts, such as chlorides and sulfates, that cannot be removed by boiling. Methods for removing permanent hardness include:
- Ion-exchange resins: These replace calcium and magnesium ions with sodium or potassium ions, softening the water.
- Adding washing soda (sodium carbonate): This reacts with the calcium and magnesium ions to form insoluble carbonates, which can then be removed.
- Distillation: This process involves heating water to produce steam, which is then condensed back into liquid form, leaving the dissolved minerals behind.
- Explain water pollution due to industrial waste.
Industrial waste can introduce harmful substances such as heavy metals (lead, mercury), toxic chemicals (pesticides, solvents), and organic pollutants (phenols, detergents) into water bodies. These pollutants can disrupt aquatic ecosystems, harm wildlife, and pose health risks to humans who consume contaminated water. The pollution may also alter the water’s pH, temperature, and turbidity, further impacting aquatic life. - Justify the statement: household water is a reason for water pollution.
Household water can contribute to pollution when it carries substances like detergents, oils, and pharmaceuticals into water bodies. Wastewater from households often contains organic matter, chemicals from cleaning products, and trace amounts of medications, which can disrupt aquatic ecosystems. Additionally, improper disposal of substances like cooking oils and paints can exacerbate water pollution. - Explain how agricultural effluents are fatal for aquatic life.
Agricultural runoff often contains fertilizers, pesticides, and animal waste, which can enter water bodies during rainfall or irrigation. Fertilizers rich in nitrogen and phosphorus cause eutrophication, leading to excessive algal growth that depletes oxygen in the water, resulting in “dead zones.” Pesticides can be toxic to aquatic organisms, affecting their reproduction and survival. - Explain five important waterborne diseases and their prevention.
- Cholera: Caused by Vibrio cholerae bacteria; prevention includes ensuring clean drinking water and good sanitation.
- Typhoid: Caused by Salmonella typhi bacteria; vaccination and using safe drinking water can prevent it.
- Dysentery: Often caused by Shigella bacteria; good hygiene and sanitation help prevent its spread.
- Hepatitis A: A viral infection spread through contaminated water; vaccination and drinking purified water are preventive measures.
- Giardiasis: Caused by the Giardia parasite; prevention includes avoiding untreated water and proper sanitation.
- Give some disadvantages of hard water.
Hard water causes scale buildup in pipes and water heaters, reducing their efficiency. It can also decrease the effectiveness of soaps and detergents, requiring more product for cleaning. Additionally, it can leave mineral deposits on dishes, laundry, and fixtures. - What is water pollution? Describe the effects of using polluted water.
Water pollution refers to the contamination of water bodies by harmful substances. Using polluted water can lead to health issues like gastrointestinal diseases, skin irritations, and neurological problems. In agriculture, polluted water can reduce crop yields and contaminate food. It also negatively affects aquatic life by disrupting ecosystems and reducing biodiversity. - Explain why water is considered a universal solvent.
Water is known as a universal solvent because it can dissolve a wide range of substances. Its polarity allows it to interact with various ionic and polar compounds, making it essential for biochemical processes, nutrient transport, and industrial applications. - Write a note on the treatment of sewage water.
Sewage treatment involves multiple stages to remove contaminants:
- Primary treatment: Physical removal of large solids through screening and sedimentation.
- Secondary treatment: Biological processes where bacteria decompose organic matter.
- Tertiary treatment: Chemical or physical processes to remove remaining contaminants, such as nitrogen, phosphorus, and pathogens. This step may involve disinfection using chlorine or UV light.
Treated water is then either released into the environment or further purified for reuse.
