Hydrosphere Overview Quiz

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Questions and Answers

What percentage of the Earth's mass is made up of water?

0.027% (correct)

70%

1.38%

Which of the following is NOT a role of water mentioned?

Nutrient carrier (correct)

Solvent

Liquid medium

Radiation transmission

What is the average residence time of water in deep layers of oceans?

1600 years (correct)

1 day

80 years

500 years

By 2025, what percentage of humans is projected to live in areas with inadequate water resources?

Two-thirds Signup and view all the answers

What is the greatest material turnover of water per year attributed to?

Evaporation and precipitation Signup and view all the answers

How many children die each year due to waterborne infections?

5 million Signup and view all the answers

What is the average residence time of water in the atmosphere?

1 day Signup and view all the answers

What fraction of Earth's surface is covered by water?

70% Signup and view all the answers

What causes the increased oxidative sedimentation in summer compared to winter?

More intensive assimilation occurs during summer Signup and view all the answers

Which of the following is true about mercury (Hg) in aquatic environments?

It accumulates in fish and becomes more toxic in anaerobic conditions Signup and view all the answers

What is a significant environmental concern related to mineral oil spills in surface water?

They dissolve insulation materials from bird feathers Signup and view all the answers

What is a consequence of oil pollutants being absorbed into sediments during winter?

They can remobilize in summer, blocking oxygen diffusion Signup and view all the answers

Which harmful byproduct can form during the chlorination of drinking water?

Chloroform Signup and view all the answers

What is the latent heat of vaporisation of water?

40.8 kJ/mol Signup and view all the answers

Which statement describes a property held by water molecules?

Water molecules can form strong hydrogen bonds with one another. Signup and view all the answers

How does the temperature affect the solubility of gases in water?

Solubility decreases with increasing temperature. Signup and view all the answers

What characterizes a thermocline in a body of water?

It is a layer with varying temperatures, creating a sharp gradient. Signup and view all the answers

What mechanism primarily determines the chemistry of shallow lakes?

The wind effects on surface water. Signup and view all the answers

What is a common consequence of high nutrient content in aquatic environments?

Enhanced growth of harmful algae. Signup and view all the answers

What is the equilibrium concentration of oxygen in water at 25°C and 1 atm pressure?

8.32 mg/l Signup and view all the answers

What is a characteristic feature of water’s dipole moment?

It enables water to stabilize charged particles and ions. Signup and view all the answers

What is the primary indicator of organic matter production in an aquatic ecosystem?

Trophity Signup and view all the answers

How long does pollution typically persist in sub-surface waters?

Decades to centuries Signup and view all the answers

Which process leads to energy loss in an aquatic ecosystem?

Saprobity Signup and view all the answers

What can excessive nutrient influx into aquatic ecosystems cause?

Oxygen depletion Signup and view all the answers

Which mass proportions are characteristic of an average biomass in aquatic ecosystems?

100:17:1 Signup and view all the answers

What characterizes the toxicity of substances polluting aquatic environments?

LD50 and LC50 values Signup and view all the answers

How does the temperature of water change as seasons progress from winter to summer in a stratified lake?

Epilimnion and hypolimnion temperatures become nearly identical in summer. Signup and view all the answers

What does increasing trophity in an ecosystem typically lead to?

Proliferation of vegetation Signup and view all the answers

What is a common source of the nutrients that contribute to eutrophication?

Municipal wastewater Signup and view all the answers

What happens to ice when subjected to pressure?

Ice melts under pressure. Signup and view all the answers

Which condition indicates acidic water based on pH?

pH < 7 Signup and view all the answers

What role does the CO2/HCO3–/CO32– buffering effect play in surface waters?

It stabilizes the pH near 8.3. Signup and view all the answers

Contrast the typical pH level of rainwater and its cause based on atmospheric conditions.

Rainwater typically has a pH of 5.63 due to dissolved CO2. Signup and view all the answers

What is the effect of temperature on the stratification of a lake during autumn and spring?

Water is completely mixed with near identical temperatures in these seasons. Signup and view all the answers

What is a key characteristic of permanent hardness in water?

It is caused by the presence of dissolved calcium and magnesium salts. Signup and view all the answers

How are redox reactions related to acid-base reactions in the hydrosphere?

Redox reactions frequently involve acid-base chemistry. Signup and view all the answers

Study Notes

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.

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Description

Test your knowledge about the hydrosphere and the critical role water plays on Earth. This quiz covers water's abundance, residence time in various environments, and future challenges in water management. Learn about the importance of water for life and its implications for the global population.