Chapter 1: Chemical Reactions and Their Effects on Water Quality PDF

# Chapter 1: Chemical Reactions and their Effects on the Water Quality ## Lesson One - In this lesson, we will study: - Water properties - Hydrosphere of planet Earth - Chemical structure of water - Chemical properties of water - Water cycle in nature ## Water - Transparent l...

# Chapter 1: Chemical Reactions and their Effects on the Water Quality ## Lesson One - In this lesson, we will study: - Water properties - Hydrosphere of planet Earth - Chemical structure of water - Chemical properties of water - Water cycle in nature ## Water - Transparent liquid that represents a medium where many chemical compounds react - Water quality and health of living organisms are dependent on the water - **Water is characterized by unique chemical properties, such as:** - It can dissolve many chemical substances. - It can be found in three states *solid - liquid - gaseous* within the known range of temperatures on Earth. ## States of Matter - **Solid state** (Ice) - **Liquid state** (Water) - **Gaseous state** (Water vapor) ## Phase Changes - **Heating:** - Solid to Liquid: Melting - Liquid to Gaseous: Evaporation - **Cooling:** - Liquid to Solid: Freezing - Gaseous to Liquid: Condensation ## Water is Necessary for Life - All living organisms' cells have a membrane (plasma membrane) through which water passes. - From the environment to inside the living cell, carrying the substances required for producing energy. - From inside the cell to outside, to get rid of wastes. ## Earth's Spheres Earth is composed of many spheres, which are: - **Atmosphere** - **Hydrosphere** - **Cryosphere** - **Lithosphere** - **Biosphere** ## Hydrosphere - Characterizes Earth from other planets in the solar system - Covers about 70% of the Earth's surface - **Distributed as follows:** - **Saltwater (about 97%):** - Oceans. - Seas. - Salty Lakes. - **Freshwater (about 1%):** - Fresh Lakes. - Groundwater. - **Frozen Water (Cryosphere):** - Polar Regions. - Mountaintops. - Glaciated Rivers. ## Aquatic Systems in Egypt - Egypt's aquatic environment is diverse - **Freshwater:** - Nile River. - Fresh Lakes. - **Saltwater:** - Red Sea. - Mediterranean Sea. - Suez Gulf. - Aqaba Gulf. - Salty Lakes. ## Water Cycle in Nature - A nearly closed system where water moves continuously from one place to another through many different pathways - **Processes involved:** - Evaporation. - Condensation. - Rain or snow falling. - Transpiration in plants. - Respiration in plants and animals. - Water infiltration (leakage) through the pores of soil and sedimentary rocks to form the *groundwater*. ## Chemical Properties of Water - Water does not exist in its pure form. - Water reacts with many ions and chemical substances. - **Three main properties of water:** - **Polarity of water:** - Oxygen atom is more electronegative than the hydrogen atom. - This results in partial negative charge on the oxygen atom and partial positive charge on the hydrogen atom. - **Water polarity results in:** - Attaching water molecules together by hydrogen bonds. This is the reason for the high boiling point of water. - **Electronegativity:** The atom's ability to attract electrons. - **Hydrogen bond:** A bond that arises among molecules containing hydrogen atoms. - **Hydrolysis of water:** - The binding of ions with water by breaking down the bonds. - **Hydrolysis takes place and leads to:** - A decrease in the concentration of hydrogen ions (H+) and an increase in the concentration of hydroxide ions (OH-). (Makes the solution alkaline) - Or, a decrease in the concentration of hydroxide ions (OH-) and an increase in the concentration of hydrogen ions (H+). (Makes the solution acidic) - **Acid-base balance:** - The concentration of hydrogen ions (H+) and hydroxide ions (OH-) - **The *pH value* :** It represents the acidity, alkalinity, or neutrality of a solution. - **Types of solutions:** - **Acidic solution:** The concentration of (H+) > The concentration of (OH-) and the pH is less than 7. - **Neutral solution:** The concentration of (OH-) = The concentration of (H+) and the pH equals 7. - **Basic solution:** The concentration of (OH-) > The concentration of (H+) and the pH is greater than 7. ## Practical Tools - **Measuring the pH values of different water samples:** **Required Tools:** - Water samples (seawater, river water, and spring water) - pH meter or pH test paper tapes - Sample cups - Distilled water (for calibration) - Stirring rod. **Procedure:** - **Using a pH meter:** - Calibrate the pH meter. - Immerse the calibrating electrode in the sample. - Record the reading. - **Using pH test paper tapes:** - Check the validity of the paper tapes. - Immerse the test paper in the sample. - Compare the color of the paper to the measuring sheet to get the pH value. **Table of pH values:** | Water Type | pH Value | Acidity or Alkalinity | Reasons | |:---------------|:--------|-----------------------|:----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | Seawater | 7.5 - 8.4 | Alkaline | According to the geographic region where the sea is located, as well as surrounding environmental factors. | | Freshwater | 6.5 - 8.5 | Acidic, neutral, or alkaline | Depends on the geographic location and the presence of impurities like dissolved gases, salts, and organic materials | | Distilled water| 7 | Neutral | Because it is devoid of most impurities and ions that share in the acidity or alkalinity of the other natural sources of water. | | Groundwater | Varies | Neutral - Alkaline | The pH value of water deep underground is affected by the presence of minerals, such as calcium or magnesium carbonate. In areas where groundwater is exposed to the surface, it can be affected by the dissolution of carbon dioxide gas and other acidic gases in the water drops. | | Clouds water | 4.5 - 5 | Weak acidic | Due to the dissolving of carbon dioxide gas and other acidic gases in the water drops that form the clouds. | ## Water Conservation and Living Organisms' Health Measures - Salt hydrolysis affects the water chemistry and can negatively affect the water quality and the health of living organisms. - It is necessary to: - Monitor salinity levels closely! - Monitor the change in the ionic composition inside the natural water surfaces! - Follow healthy and right activities to get rid of wastes: - Reduce adding harmful salts to the water surface. - Keep the water quality for all the habitats of wildlife and human consumption. ## Lesson Two - Physical Properties of Water and Their Role in the Distribution of Living Organisms ## Density - Definition: The mass of a unit volume of matter at a given temperature. - **Formula:** Density = Mass/Volume - **SI unit:** kg/m³. - **Other units:** g/cm³, g/L. - **Device for measuring:** Hydrometer. ### Factors that affect density - The mass of the molecules. - The distance between the molecules (intermolecular spaces). - The purity of the substance (the percentage of impurities). - Temperature. ### Relative Density - The ratio of the density of a substance to the density of pure water at the same temperature. ### Water Density - Generally, the density of a liquid decreases as its temperature increases. - Water's density between 0°C and 4°C: - Density increases as temperature decreases. - Reaches its maximum density at 4°C (1 g/cm3 or 1000 kg/m3) - Decreases as temperature increases. - This unique behavior explains: - **Why bodies of water in polar regions begin to freeze from the surface rather than the bottom:** - When the water temperature drops below 4°C, water layers less than 4°C become less dense, and these layers float on top of the warmer water below. - When the surface layer freezes, the ice layer remains floating, and the water below remains at a temperature of 4°C. - **Water currents in the oceans:** - The movement of water from one region to another, carrying heat, salt, and nutrients. - **Factors influencing water currents:** - Water pressure. - Water temperature. - Water salinity. ## Practical Experiment: The effect of density on the melting of ice **Steps:** 1. Prepare two identical ice cubes by freezing pure water and adding food dye. 2. Fill two cups with equal quantities of water, one with freshwater and one with saltwater. 3. Place an ice cube in each container. 4. Observe the movement of water around the ice cubes. **Observations:** - The ice cube in freshwater melts faster than the ice cube in saltwater. - The dye from the freshwater ice cube spreads throughout the water, while the dye from the saltwater ice cube mostly spreads on the surface. **Explanation:** - When the ice cube in freshwater melts, the cold water sinks to the bottom, and warmer water rises. This is because the density of cold water is greater than the density of warm water. - When the ice cube in saltwater melts, the cold water remains on the surface. This is because the cold water is less dense than the saltwater, and so it floats on top. This creates a layer of cold water around the ice cube, slowing down the melting process. ## Understanding Water Currents - Differences in density at different parts of the ocean drive water currents. - **Factors influencing water density:** - **Water pressure:** Pressure increases as depth increases, causing the water molecules to come closer together, decreasing the volume and increasing the density. - **Water temperature:** The intermolecular distances decrease as temperature decreases to 4°C, increasing density. From 4°C to 0°C, the intermolecular distances increase, decreasing density. - **Water salinity:** The higher the salinity of water, the higher its density. ## Miscellaneous Questions **Questions:** - What is the scientific term for a substance that can flow and doesn’t have a fixed shape but takes the shape of its container? - Explain why the density of a pure substance does not change when the mass or volume of the sample taken from it changes. - What happens when the temperature of a body is increased concerning its density? - Name two factors on which the density of a substance depends. - Explain why the temperature at the bottom of lakes in polar regions doesn’t drop below 4°C. - How does the density of water change as the temperature decreases from 4°C to 0°C? - What happens to the volume of a quantity of pure water when it freezes? - Explain how the behavior of water differs from that of other liquids when studying the effect of changing temperature on density. - Give an example of how the changes in temperature and water density can affect living organisms in an aquatic environment. - How can you increase the density of pure water at room temperature in two methods? - Mention the factors that affect the density of water in the oceans and explain the effect of each. - What is the difference between a covalent bond and a hydrogen bond? - Explain why the density of water is greater at point Y than at point X. **Answers:** - **Fluid** - The density of a pure substance does not change when the mass or volume of the sample taken from it changes, because density is a characteristic physical property of a substance. - As the temperature of a body increases, the kinetic energy of the particles increases, causing them to move further apart. This leads to an increase in the volume and a decrease in the density. - Two factors on which the density of a substance depends are the mass of the molecules and the intermolecular spaces between the molecules. - The temperature at the bottom of lakes in polar regions doesn’t drop below 4°C because the surface layer of water freezes into ice, which floats on the surface of the water. The ice layer acts as a thermal insulator, preventing the water below it from freezing. - As the temperature of water decreases from 4°C to 0°C, the intermolecular distances between the molecules increase, causing the volume of the water to expand and decreasing its density. - The volume of a quantity of pure water increases when it freezes as the density of ice is less than the density of water. - Water exhibits an anomalous expansion when its temperature decreases from 4°C to 0°C. This is because the density of water increases as the temperature decreases from 4°C to 0°C, and then it decreases as the temperature decreases further from 0°C to 4°C. - The changes in temperature and water density can affect living organisms in an aquatic environment in many ways. For example, cold water is denser than warm water, so cold water will sink to the bottom of a lake or ocean, creating a thermocline. This thermocline can limit the distribution of marine species, since some species are adapted to live in different temperature ranges. - You can increase the density of pure water at room temperature in two methods: - Adding a solute to the water: Adding solutes makes the water heavier. - Increasing the pressure: Increasing the pressure on the water forces the molecules closer together, decreasing the volume and increasing the density. - Several factors affect the density of water in the oceans. These include: - **Temperature:** Colder water is denser than warmer water. - **Salinity:** The higher the salinity of water, the higher its density. - **Pressure:** Pressure increases as depth increases, causing water molecules to come closer together, decreasing the volume and increasing the density. - The covalent bond is a strong bond that results from the sharing of electrons between two atoms. The hydrogen bond is a weaker bond that results from the attraction between a hydrogen atom that is covalently bonded to a highly electronegative atom and a lone pair of electrons on an adjacent electronegative atom. - The density of water is greater at point Y than at point X because the water at point Y is at a greater depth. As pressure increases with depth, water molecules are forced together, decreasing their volume and increasing their density. - The temperature at the bottom of lakes in polar regions doesn't drop below 4°C because when the surface layer of water freezes, the ice layer forms an insulating layer that prevents the water below it from freezing. The ice layer acts as a thermal insulator, preventing the water below it from freezing. - A measurement that expresses the concentrations of hydrogen and hydroxide ions *pH* .