Integrated Sciences Sec.1 Unit One - Chapter One 2025 PDF

# Integrated Sciences - Sec.1 First Term ## Unit One - Chapter One: Aquatic Ecosystem (Part 1) ### Name: Mr. Ahmed Elbasha Mob.: 01153233911 # The Effects of Chemical Reactions on Water Quality Water's unique properties make it vital for life. It's ability to dissolve substances and exist in d...

# Integrated Sciences - Sec.1 First Term ## Unit One - Chapter One: Aquatic Ecosystem (Part 1) ### Name: Mr. Ahmed Elbasha Mob.: 01153233911 # The Effects of Chemical Reactions on Water Quality Water's unique properties make it vital for life. It's ability to dissolve substances and exist in different states is crucial for life processes. Water is essential for all living things, from tiny microbes to large animals. It moves into cells, providing nutrients and removing waste. Water, covering approximately 70% of Earth's surface, sets our planet apart from others in the solar system. This vast amount of water, known as the hydrosphere, is divided into: | Type | Description | |-----------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | Salty water | Existing in oceans, seas, and saltwater lakes. | | Freshwater | Only a small portion is freshwater found in rivers, lakes, and underground. Water vapor contributes to the atmosphere, while frozen water is found in polar regions and glaciers. | ## Hydrological Cycle The water cycle is a continuous process that moves water around Earth. Water evaporates from bodies of water and land, rises into the atmosphere, condenses to form clouds, and falls back to Earth as precipitation. This cycle is influenced by various processes, including transpiration from plants, infiltration into the ground, and chemical reactions that can lead to acid rain. ## Chemical Composition of Water Water is composed of two elements: hydrogen and oxygen. ### Hydrogen and oxygen combine in a 2:1 ratio | By Volume | By Mass | |-----------|-----------------------------------| | 2:1 | Oxygen accounts for approximately 88.89% of a water molecule, while hydrogen constitutes about 11.11%. | However, the two hydrogen atoms are covalently bonded to a single oxygen atom with a bond angle of approximately $104.5^\circ$ degrees. ## Chemical Properties of Water Water, as found on Earth, is rarely pure. It typically contains various ions and chemical substances that interact with it in numerous ways. Let's explore three of water's primary chemical properties: ### 1. Polarity of Water The oxygen atom in a water molecule has a much higher electronegativity than the hydrogen atoms. This causes the electrons in the covalent bonds to be pulled more strongly towards the oxygen atom. As a result, the oxygen atom carries a partial negative charge ($δ-$), while the hydrogen atoms carry partial positive charges ($δ+$). This uneven distribution of charge gives the water molecule a polar character. It allows water to dissolve a wide range of substances, transport nutrients, and participate in numerous biological processes. **Example:** Salt (NaCl) dissolves in water because the positive sodium ions are attracted to the negative oxygen end of water molecules, while the negative chloride ions are attracted to the positive hydrogen end. ### 2. Hydrolysis A small percentage of water molecules exist as hydrogen ions (H+) and hydroxide ions (OH-). Chemical reactions with various compounds can cause hydrolysis of certain salts present in natural water, affecting the balance of these ions and resulting in the acidity or alkalinity of the water. **Practical Example:** - When table salt (NaCl) is added to water, it dissociates into sodium ions (Na+) and chloride ions (Cl-). These ions remain in the solution without interacting with water ions, making the solution neutral because the concentration of hydrogen ions (H+) is equal to the concentration of hydroxide ions (OH-). - However, in the case of sodium bicarbonate (NaHCO3), hydrolysis occurs, leading to a decrease in the concentration of hydrogen ions (H+) and an increase in the concentration of hydroxide ions (OH-) making the salt solution basic. $HCO_3^- + H_2O \rightarrow H_2CO_3 + OH^-$ - The opposite occurs when ammonium chloride (NH4Cl) is dissolved in water, which undergoes hydrolysis and causes a decrease in the concentration of hydroxide ions and an increase in the concentration of hydrogen ions, making the salt solution acidic. $NH_4^+ + H_2O \rightarrow NH_3 + H_3O^+$ ### 3. Acid-Base Balance The acid-base balance in water depends on the relationship between the concentration of hydrogen ions (H+) and hydroxide ions (OH-). This relationship can be determined by measuring the **pH** of the solution. pH is a scale ranging from 0 to 14. - If the concentration of H+ ions increases, the water becomes acidic and the pH value is less than 7. - Conversely, if the concentration of OH- ions increases, the water becomes basic and the pH value is greater than 7. - When the concentrations of H+ and OH- ions are equal, the water is neutral and the pH value is 7. **pH:** It is a measure of how acidic or basic a solution is. Pure water has a pH of approximately 7, which is considered neutral. However, this value can vary in natural environments, affecting the organisms that live there. ## pH Examples 1. The pH of seawater generally ranges from 7.5 to 8.4, depending on the specific location and surrounding environmental factors. 2. Freshwater in rivers and lakes typically has a pH range of 6.5 to 8.5. 3. Distilled water has a pH of approximately 7, as it is devoid of most impurities and ions that contribute to the acidity or alkalinity of other natural water sources. 4. The pH of groundwater varies from one region to another, primarily due to the underlying rock composition. Groundwater is often neutral or alkaline, with pH values influenced by the presence of calcium carbonate or magnesium carbonate rocks. 5. Cloud water is generally slightly acidic, with a pH ranging from 4.5 to 5. This acidity is primarily due to the presence of dissolved carbon dioxide and other acidic gases in water droplets." Mr. Ahmed Elbasha Mob.: 01153233911