Water Chapter Notes | Chemistry for JAMB PDF Download

Water is an essential and versatile compound that plays a vital role in various chemical and biological processes. Understanding its properties, composition, and behavior is crucial in chemistry. 

Introduction to Water

• Chemical formula: Water is represented by the chemical formula H₂O, indicating two hydrogen atoms bonded to one oxygen atom.
• Molecular structure: Water molecules have a bent shape due to the presence of two lone pairs of electrons on the oxygen atom.
• Polarity: Water is a polar molecule, with the oxygen atom being slightly negative and the hydrogen atoms being slightly positive. This polarity gives water its unique properties.

Physical Properties of Water

• State of matter: Water exists in all three states of matter—solid (ice), liquid (water), and gas (water vapor)—under normal conditions.
• Density: Water has a maximum density at 4°C, causing ice to float on liquid water.
• High boiling and melting points: Water has high boiling and melting points compared to other compounds of similar molecular weight.
• High specific heat capacity: Water has a high capacity to absorb and store heat, making it an excellent regulator of temperature.
• High heat of vaporization: Water requires a significant amount of heat energy to convert from liquid to gas, allowing it to act as a coolant.

Water as a Solvent

• Solvent properties: Water is often called the "universal solvent" due to its ability to dissolve a wide range of substances.
• Polarity and hydrogen bonding: Water's polarity and ability to form hydrogen bonds make it effective at dissolving polar and ionic compounds.
• Biological significance: Water's solvent properties are crucial for various biological processes, such as transport of nutrients, waste removal, and cellular reactions.

Dissolved Atmospheric Gases in Water

• Common gases: Water can dissolve several atmospheric gases, including oxygen (O₂), carbon dioxide (CO₂), and nitrogen (N₂).
• Biological significance: Dissolved oxygen supports aquatic life by enabling respiration, while dissolved carbon dioxide is involved in photosynthesis and pH regulation.
• Impact on water quality: The presence of dissolved gases affects the chemical balance, pH, and overall health of aquatic ecosystems.

Hard and Soft Water

• Hard water: Contains high concentrations of dissolved minerals, primarily calcium (Ca²⁺) and magnesium (Mg²⁺) ions.
• Soft water: Has low concentrations of calcium and magnesium ions.
• Temporary hardness: Caused by the presence of bicarbonate ions (HCO^3-) which can be removed by boiling or adding lime (calcium hydroxide).
• Permanent hardness: Caused by dissolved sulfates, chlorides, or nitrates of calcium and magnesium, requiring specific methods for removal.

Treatment of Water for Town Supply

• Coagulation and flocculation: Chemicals are added to water to form flocs, which trap impurities and suspended solids.
• Sedimentation: Water is allowed to settle, and the flocs settle to the bottom.
• Filtration: Water passes through filters to remove smaller particles and impurities.
• Disinfection: Chemicals like chlorine or ozone are added to kill microorganisms.
• pH adjustment: The pH of water may be adjusted for taste and to prevent corrosion.
• Storage and distribution: Treated water is stored and distributed through a network of pipes.

Water of Crystallization and Related Phenomena

• Water of crystallization: Water molecules incorporated into the crystal structure of certain compounds during their formation.
• Efflorescence: Crystalline substances losing water of crystallization upon exposure to air, resulting in powdery deposits.
• Deliquescence: Substances absorbing moisture from the air and dissolving in it, forming a solution.
• Hygroscopy: Substances attracting and holding water molecules from the surrounding environment, causing moistness or dissolution.
• Examples of compounds: Copper sulfate pentahydrate, gypsum, sodium carbonate, calcium chloride, silica gel, common salt.

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