Introduction to Chemistry of Water

Introduction to Chemistry of Water

• Water is crucial for life and regulates Earth's temperature.
• Water is a universal solvent with multiple applications in various sectors (industrial, agricultural, domestic).
• Water has renewable energy potential (hydropower and steam).

Properties of Water: Structure

• A water molecule (H₂O) consists of two hydrogen atoms covalently bonded to an oxygen atom.
• Covalent bonds hold the molecule together.
• Other bond types exist including ionic, metal, and hydrogen bonds.

Properties of Water: Polarity

• Water molecules are polar due to unequal electron sharing in polar covalent bonds.
• This creates partial positive charges on hydrogen atoms and a partial negative charge on the oxygen atom.
• Polarity is due to the uneven distribution of electrons.

Properties of Water: Physical Properties

• Water exists in three states: solid (ice), liquid, and gas (water vapor).
• Hydrogen bonds are responsible for water's high boiling and melting points, compared to similar molecules.
• The density of ice is lower than liquid water, making ice float, a crucial property of aquatic life.

Properties of Water: Density

• Solid ice (0.9167 g/mL) is less dense than liquid water (0.9998 g/mL).
• Water vapor density (~0.0006 g/mL) varies with temperature and pressure.

Properties of Water: Additional Properties

• Molecular formula: H₂O
• Molecular weight: 18.0160 g/mol
• Molecular geometry: Bent (V-shaped)
• Boiling point: 100 °C
• Freezing point: 0 °C
• Density at 4°C: 1 g/mL or 1000 kg/m³
• Polarity: Polar
• pH: 7

Properties of Water: Key Properties

• High specific heat: Water absorbs and retains heat effectively, maintaining stable temperatures in environments.
• High heat of vaporization: A large amount of energy is needed to convert water to vapor, which assists in cooling.
• Adhesion and cohesion: Water adheres to other surfaces and cohere, facilitating processes like capillary action in plants.
• Surface tension: Water has a "skin" due to cohesive forces, facilitating movement for small organisms.

Water and Environment: Water Pollution

• Only 1% of Earth's water is fresh and accessible.
• Saline water (97%) is mostly in oceans, unsuitable for drinking.
• Freshwater (2%) is mostly in ice caps and glaciers, largely inaccessible.
• Accessible freshwater is a minute portion (less than 1%) for humans.

Water Pollution: Causes

• Chemical contaminants (pesticides, heavy metals)
• Biological pollutants (e.g., E. coli)
• Radioactive pollutants (nuclear waste)

Water Pollution: Impacts

• Health risks
• Reduced water quality
• Ecological damage

Water Analysis: Methods

• Temperature Testing: Measures the rate of biochemical reactions and oxygen retention.
• pH Testing: Measures the acidity of water. Most aquatic life thrives in a pH range of 6 to 8.
• Dissolved Oxygen Test: Measures the amount of oxygen dissolved in water, essential for aquatic life respiration.
• Chloride Test: Measures chloride levels in water, influenced by minerals and industrial pollution.
• Turbidity Test: Measures suspended particles (water clarity), high turbidity impacts photosynthesis and water temperature.
• Metal Test: Detects harmful heavy metals (Lead, Mercury, Arsenic, Cadmium).

Water Treatment: Processes

• Coagulation: Adding aluminum sulfate or polymers to cause particles to clump (flocculate).
• Sedimentation: Allowing flocs to settle to the bottom of basins.
• Filtration: Removing particulate matter by passing water through filters (gravel, sand, activated carbon).
• Disinfection: Adding disinfectants (e.g., chlorine) to kill microorganisms.
• pH Correction: Adjusting pH with lime to stabilize soft water.