Hydrosphere Overview Quiz

Hydrosphere

• Water is the most abundant molecule on Earth, representing 8% of its top layer.
• Life on Earth depends on water, which acts as a solvent, influences chemical reactions, and regulates various life processes.

Water on Earth

• Earth's surface is covered by water, with an average depth of ~4267 meters.
• The total amount of water on Earth is estimated to be enough to fill a sphere with a diameter of 1400 km.

Water Residence Time

• The average time water spends in different environments:
  • Atmosphere: 1 day
  • Lakes and rivers: 7 years
  • Surface ocean layers: 80 years
  • Deep ocean layers: 1600 years
  • Polar ice and glaciers: 500 years

Water Use and Management

• The United Nations predicts water scarcity will be a major environmental issue by 2025, with two-thirds of the world's population affected.
• Currently, 1 billion individuals have access only to polluted water, leading to 5 million child deaths annually from waterborne infections.

Hydrological cycle

• The continuous movement of water through the Earth's atmosphere, oceans, and land.

Properties of Water

• Water is polar with a high dipole moment, leading to strong hydrogen bond formation.
• Hydrogen bonds contribute to water's relatively high boiling point, compared to nonpolar molecules with similar molecular weights.

Water Density and Temperature

• Water reaches its maximum density at 4°C.
• This property influences ice formation and glacier movement.

Water as a Solvent

• Water's high dipole moment & dielectric constant facilitate the solvation of charged particles & polar molecules.
• This leads to the formation of solvate spheres around ions.
• Despite water's low conductivity, dissolved ions increase its conductivity.

Water Associations

• Water interacts with both polar and nonpolar molecules.
• It forms associations with polar molecules through hydrogen bonds, leading to solvation spheres.
• Nonpolar molecules aggregate in water due to hydrophobic interactions, forming micelles.

Measures of Particles in Water

• Nanoparticles: 10^-9 - 10^-7 meters (1-100 nm).
• Aitken particles: airborne particles < 0.1 µm (100 nm) larger than molecules and small ions.

Solubility of Gases in Water

• Gas solubility decreases with increasing temperature.
• The concentration of dissolved gases is crucial for aquatic organisms, especially oxygen.
• Oxygen depletion causes fish deaths, while high nutrient content can lead to eutrophication.

Oxygen in Water

• The majority of water's oxygen comes from the surface through convection and diffusion.
• Oxygen solubility depends on temperature, partial pressure of atmospheric oxygen, and salinity.
• The equilibrium concentration of oxygen in water is 8.32 mg/l (1 atm, 25 °C).

Thermocline

• A distinct layer within a body of water where temperature changes rapidly with depth.

Lake Stratification

• Lake water exhibits seasonal stratification, with distinct layers based on temperature:
  • Epilimnion: warmer, surface layer
  • Hypolimnion: colder, bottom layer

Autoprotolysis of Water and pH

• Water undergoes autoprotolysis, forming H+ and OH- ions.
• pH is a measure of acidity:
  • pH < 7: acidic
  • pH > 7: basic
  • pH = 7: neutral

Strength of Acids and Bases

• Strong acids displace weaker acids from their salts.

CO2-Bicarbonate-Carbonate Equilibrium

• This buffer system plays a critical role in surface waters.
• It maintains a pH of 8.3 by buffering against external acidity or alkalinity.

Carbon Dioxide in Water

• The partial pressure of CO2 in air is 3.68 x 10^-4 atm, leading to a pH of 5.63 for rainwater.
• Water's CO2 content often exceeds atmospheric levels due to exchange with dissolved carbonate minerals.
• Natural waters are typically slightly acidic due to dissolved CO2.

Alkalinity

• Alkalinity arises from dissolved cations, such as Ca²⁺ and Na⁺.

Salt Concentration

• The average salt concentration in oceans and seas is 3.5%.
• Rivers are the primary source of dissolved salts.

Water Hardness

• Refers to the concentration of dissolved calcium and magnesium ions:
  • Temporary hardness: caused by dissolved bicarbonate ions, removed by boiling.
  • Permanent hardness: caused by dissolved sulfates and chloride ions, not removable by boiling.

Redox Conditions

• Redox reactions are prevalent in aquatic environments, often driven by microbial processes.
• They often involve acid-base interactions.

Temporal Effects of Pollutants

• Surface water has a quicker recovery time from pollution than groundwater.
• Persistent pollutants, like DDT, remain in the environment for extended periods, leading to bioaccumulation in aquatic life.

Trophity and Eutrophication

• Trophity indicates the rate of organic matter production in an ecosystem.
• Eutrophication is a process where excess nutrients, particularly nitrogen and phosphorus, cause excessive algal growth.

Saprobity

• Saprobity measures the decomposition rate of organic matter in a water body.
• High organic matter content leads to increased microbial activity, consuming dissolved oxygen.

Toxicity

• Toxicity refers to the harmful effects of substances on aquatic organisms.
• It's assessed through chemical analysis & biological tests.
• LD50 and LC50 values characterize the dosage/concentration needed for 50% mortality.

Heavy Metal Pollution

• Mercury (Hg) is a neurotoxin, accumulative in fish.
• Methylation of Hg under anaerobic conditions increases its toxicity.
• Lead (Pb) deposition affects sedimentation patterns.

Groundwater Transport of Pollution

• Mineral oil pollution occurs when oil spills into surface water.
• Containment methods involve barriers like perlite, cellulose, or wool.
• Mineral oil harms animals by dissolving fats, disrupting their insulation.

Water Purification

• Natural biofilters in bank-filtered wells contribute to clean drinking water.

Chlorination Side Products

• Chlorination of water produces hazardous byproducts:
  • Chloroform: a carcinogenic poison
  • Chlorinated alkylphenols: disrupt hormone function
  • Oxidized PAHs: carcinogenic and mutagenic

These notes focus on crucial aspects of the chemistry of the hydrosphere, highlighting key concepts, processes, and environmental implications.