Water Chemistry and Environmental Impact Flashcards

Chemical Reactions and Their Impact on Water Quality

Introduction

• Water is not just a transparent liquid but a medium in which many chemical compounds can react, affecting the quality of water and the health of living organisms that depend on it.
• The chapter will cover the hydrosphere and its role in nature, basic physical properties and chemical reactions in water, and how these properties and reactions affect environmental components.

1. Properties and Importance of Water

Physical Properties

• Water has unique properties that support life, such as the ability to dissolve many chemical substances.
• Water can exist in three states: solid (ice), liquid (water), and gas (water vapor) within the temperature range on Earth’s surface.

Importance of Water in Life

• Water is essential for life on Earth, and all life forms contain a membrane separating the organism from its environment.
• Water carries materials needed to produce energy into the living cell from the environment and removes waste products out of it through this membrane.

2. Different Envelopes on Planet Earth

Hydrosphere

• The hydrosphere distinguishes Earth from other planets in the solar system, referring to water in the liquid state, covering about 70% of the Earth’s surface.

Saltwater and Freshwater

• Saltwater: Makes up about 97% of the liquid water on Earth’s surface, mainly in oceans, seas, and salt lakes.
• Freshwater: Makes up the remaining liquid water on the Earth’s surface, found in rivers, freshwater lakes, and groundwater, representing about 3% of the total water.

Water Vapor

• In the gaseous state, water vapor is a component of the atmosphere.

Cryosphere

• Refers to frozen water in polar regions, mountain peaks, and glaciers.

Aquatic Environment in Egypt

• Egypt features a diverse aquatic environment, including:
  • The Nile River (the longest river in the world).
  • The Gulf of Suez and the Gulf of Aqaba (parts of the Red Sea).
  • The Red Sea (characterized by diverse marine life).
  • The Mediterranean Sea (extends along Egypt’s northern coasts).
  • Numerous saltwater and freshwater lakes.

3. The Water Cycle in Nature

Continuous Changes in Water States

• Water exists on or near the Earth’s surface in a state of continuous change among its three forms.
• Water constantly moves from one place to another through different pathways, forming a nearly closed system known as the water cycle or hydrologic cycle.

Hydrologic Cycle

• The hydrologic cycle is the continuous natural process through which water is transferred between the Earth’s surface and the atmosphere.
• The cycle starts with evaporation from oceans and lakes, vapor condenses to form clouds, and water precipitates as rain or snow.
• Water flows through streams and rivers into oceans, part of it seeps into the soil to form groundwater, and another part returns to the atmosphere through evaporation, which keeps the cycle continuous.

Main Processes in the Hydrologic Cycle

• Evaporation: The process of converting water from liquid to gaseous state, contributing to cloud formation.
• Precipitation: The process of rain or snow falling on the Earth.
• Transpiration and Respiration: Biological processes such as transpiration in plants and respiration in plants and animals.
• Water Infiltration: Seepage of water through soil pores and sedimentary rocks to form groundwater.

Chemical Reactions in Clouds

• Water vapor in clouds can chemically react with compounds in the air, forming acids that may fall as acid rain.
• Acid rain can dissolve rocks and change environmental properties.

Comparisons

• Saltwater:
  • Forms the majority of Earth's water (97%) and is found in oceans and seas.
• Freshwater:
  • Forms a small percentage (3%) but is essential for life on Earth.
• Water Cycle:
  • Includes all processes that transfer water between the Earth and the air.
• Infiltration:
  • A specific process within the cycle where water penetrates through the soil and rocks to form groundwater.

Physical Nature of Water

• Water can exist in multiple physical states: solid (ice), liquid (water), gas (water vapor), while most other chemical substances cannot transition between states as easily.

Tools and Measurements for Measuring Rainfall

• Several tools and methods are used to measure rainfall amounts and precipitation in a specific area:

1. Rain Gauge

• Mechanical Type: Uses a system of pipes and channels to measure the amount of water falling.
• Electronic Type: Includes electronic sensors that measure the amount accurately and convert it to digital data.

2. Weather Stations

• Include a collection of tools such as rain gauges, humidity measuring instruments, and atmospheric pressure measuring devices that work together to provide comprehensive weather data, including rainfall amount.

3. Satellites

• Use remote sensing techniques to measure the amount of rainfall on a large scale.
• Satellites can accurately measure amounts by imaging the Earth’s surface and analyzing data from infrared and microwave radiation.

4. Weather Radars

• Used to measure the intensity of rainfall by sending radio waves and receiving them after they are reflected by raindrops.
• Radars provide data on the distribution and intensity of rainfall.

5. Portable Devices

• Include tools such as portable rain gauges used in field and research studies to obtain accurate data from specific areas.

Predicting Future Changes in the Water Cycle on Earth

• Scientists can predict future changes in the water cycle on Earth, but these predictions depend on several factors and models:

1. Climate Models

• Climate simulation models are used to predict changes in the water cycle based on current data and potential climate variables such as increased temperatures and changes in rainfall patterns.

2. Historical Data Analysis

• Historical data on changes in rainfall, evaporation, and precipitation patterns can help predict future trends in the water cycle.

3. Climate Change Research

• Studying the effects of climate change on the water cycle, such as changes in evaporation rates, rainfall distribution, and glacial melt, helps anticipate future changes.

4. Estimates of Human Impact

• Include assessing human impacts on the water cycle such as water usage, water pollution, and changes in land use.

Chemical Composition of Water

• Water is composed of two elements: hydrogen and oxygen, in a ratio of 2:1 by volume.
• The chemical composition can be summarized as follows:

Atomic Composition

• A water molecule consists of two hydrogen atoms and one oxygen atom. The hydrogen atoms are bonded to the oxygen atom through covalent bonds.

Percentage by Mass

• Oxygen represents about 88.89% of the mass of a water molecule.
• Hydrogen represents about 11.11% of the mass of a water molecule.

Angle Between Bonds

• The covalent bonds between the two hydrogen atoms and the oxygen atom form an angle of about 104.5 degrees.

Chemical Properties of Water

• Water contains many ions and chemical substances, and we will review three major chemical properties:

1. Polarity

• Description: Water is characterized by molecular polarity due to the difference in electronegativity between the oxygen atom and the two hydrogen atoms.
• Electrons are attracted towards the oxygen atom, making it relatively negatively charged, while the two hydrogen atoms gain a relative positive charge.
• Results: This polarity allows water to form hydrogen bonds with other water molecules and with other polar molecules, which contributes to dissolving many salts and breaking them down into hydrated ions.

Hydrated Ions

• Hydrated ions are ions formed when chemical substances react with water and form hydrates, meaning the ions are surrounded by water molecules.
• In this context, "hydrated" means the ions are part of an aqueous compound consisting of ions and water molecules.

Example of Hydrated Ions

• When sodium chloride (NaCl) dissolves in water, the salt breaks down into sodium ions (Na⁺) and chloride ions (Cl⁻).
• In water, these ions are surrounded by water molecules, where the water molecules are arranged around each ion in an organized system known as hydration.

Example:

• Capacity to Dissolve Substances: Water is known as the "universal solvent" because it can dissolve a wide range of compounds due to its polar nature.

Polar Nature

• Refers to the presence of an unequal distribution of electrical charges within a molecule, leading to the formation of positively and negatively charged regions.
• In polar molecules, there are atoms with higher electronegativity (such as oxygen in water) and others with lower electronegativity (such as hydrogen), which makes the molecule have poles.

Interaction with Chemical Substances

• Water interacts with chemical substances in multiple ways, making it an effective medium in many chemical reactions.

Dissolving Sodium Chloride in Water

• When sodium chloride (NaCl) dissolves in water, a physical reaction occurs in which the salt is separated into sodium ions (Na⁺) and chloride ions (Cl⁻). This happens as follows:

1. Reaction:

• NaCl (solid) \rightarrow Na⁺ (dissolved) + Cl⁻ (dissolved)

2. Analysis:

• The salt reacts with water in a process known as hydrolysis, where both sodium ions and chloride ions are distributed in the water, but these ions do not react with the water to cause a change in the acidity or alkalinity of the solution.

3. Result:

• Because sodium chloride does not change the concentration of hydrogen ions (H⁺) or hydroxide ions (OH⁻), the resulting solution is neutral, meaning the concentration of hydrogen ions equals the concentration of hydroxide ions.

Hydrogen Bonds and Boiling Point of Water

• The ability to form hydrogen bonds between water molecules is a major reason for the high boiling point of water compared to other compounds that have the same basic structure:

1. Hydrogen Bonds:

• Water (H₂O) has a strong ability to form hydrogen bonds between its molecules, because the oxygen atom in the water molecule has a relative negative charge that attracts hydrogen atoms from other water molecules.

2. Boiling Point:

• As a result of these hydrogen bonds, water molecules need a greater amount of energy to break apart and transition from the liquid state to the gaseous state. Therefore, the boiling point of pure water reaches 100 degrees Celsius under normal atmospheric pressure.

3. Comparison:

• In contrast, hydrogen sulfide (H₂S) does not form strong hydrogen bonds like water, so its boiling point is low, about -61 degrees Celsius.

Hydrolysis and Solvolysis

• Hydrolysis is the process in which water reacts with different compounds to form hydrogen ions and hydroxide ions:

1. Hydrolysis in Salts:

• In some salts, such as sodium bicarbonate (NaHCO₃) and ammonium chloride (NH₄Cl), hydrolysis occurs when they are dissolved in water.

2. Examples:

• Sodium Bicarbonate Salt (NaHCO₃):
  • When dissolved in water, it reacts and hydrolyzes, leading to a decrease in hydrogen ions and an increase in the concentration of hydroxide ions, making the solution alkaline.
• Ammonium Chloride Salt (NH₄Cl):
  • When dissolved in water, it hydrolyzes, causing a decrease in the concentration of hydroxide ions and an increase in the concentration of hydrogen ions, making the solution acidic.

Acid-Base Balance

• The acid-base balance in water depends on the relationship between the concentration of hydrogen ions and hydroxide ions, and it is measured using the pH value:

1. pH Value:

• pH is a measure of the acidity or alkalinity of a solution, ranging from 0 to 14.
  • pH < 7: Indicates acidity of the solution (high concentration of hydrogen ions).
  • pH > 7: Indicates alkalinity of the solution (high concentration of hydroxide ions).
  • pH = 7: Indicates a neutral solution (balance between the concentration of hydrogen ions and hydroxide ions).

2. Effects of Environmental Changes:

• The pH value in natural environments may vary due to the effects of different environmental factors such as pollution, which may affect the living organisms in these environment.

Conclusion

• The presented examples embody the effect of different chemical reactions on the properties of water, from dissolving salts to reacting with water and forming ions, and how this affects the properties of solutions and the boiling point of water. They also demonstrate the significance of the pH value in determining the acidity or alkalinity of the solution and the consequences of this on the living environment.

pH Values of Water from Different Sources

1. Seawater:

• pH Value: Usually ranges between 7.5 and 8.4.
• Influencing Factors: The value varies depending on the geographical location and environmental factors such as pollution and weather conditions. Saltwater tends to be slightly alkaline due to the interaction of the ions present in it.

2. Freshwater (Rivers and Lakes):

• pH Value: Usually ranges between 6.5 and 8.5.
• Influencing Factors: The value is affected by environmental factors such as rainfall, water flow, and interaction with soil and rocks.

3. Distilled Water:

• pH Value: Approximately 7.
• Influencing Factors: Distilled water is free from most impurities and ions that contribute to acidity or alkalinity, so it is generally neutral.

4. Groundwater:

• pH Value: Varies from one region to another.
• Influencing Factors: Depends on the geological composition of the rocks in the area. Groundwater can be neutral or alkaline, and its value varies based on the interaction with rocks such as calcium carbonate and magnesium carbonate.

5. Clouds:

• pH Value: Usually ranges between 4.5 and 5.
• Influencing Factors: The pH of clouds is slightly acidic due to the presence of carbon dioxide and other acidic gases dissolved in the water droplets.

Note:

• The mentioned values can vary based on different environmental factors and human activities that affect the pH level in those areas.

Points to Focus On:

• Industrial Pollutants: In industrial cities, acids in rain may increase due to emissions.
• Agricultural Practices: In agricultural areas, fertilizers and pesticides may affect the pH of rain.
• Salinity and Evaporation: In coastal cities, the evaporation of seawater can affect the pH of rain.

Salinity and Its Impact on Water Quality and the Health of Living Organisms

Salinity and Hydrolysis:

• Impact: The hydrolysis of some salts can lead to a change in the ionic composition of water, affecting its quality. It is important to continuously monitor salinity levels to minimize negative impacts.

Waste Disposal:

• Proper Practices: Reduce the addition of harmful salts to water bodies by following proper waste disposal practices. This helps maintain the quality of water and the health of the living organisms that depend on it.