SLM11-SCI-1-Chemistry-of-Water PDF

Chemistry for Engineers SCI 1  At the end of the lesson, students should be able to: Identify the different composition of water. Explain why water is polar. Explain hydrogen bonding in water. Explain the symmetry of water molecule. Differentiate cohesion and adhesion. State why wat...

Chemistry for Engineers SCI 1  At the end of the lesson, students should be able to: Identify the different composition of water. Explain why water is polar. Explain hydrogen bonding in water. Explain the symmetry of water molecule. Differentiate cohesion and adhesion. State why water has high specific heat and its importance in the surroundings.  At the end of the lesson, students should be able to: State the importance of water’s high heat of evaporation. State the importance of ice having lower density. Discuss the different phases of water. Discuss why water is a universal solvent. State the different reactivity of water to the different groups in the periodic table. Water, covering 75% of Earth's surface, is the most abundant compound in living organisms and naturally exists as a gas, liquid, and solid. It is found in oceans, lakes, rivers, streams, groundwater, ice sheets on the North and South Poles, and snow. The gaseous form, water vapor, exists in the atmosphere. Water is a vital substance that sets Earth apart from other planets and is essential for life development and nourishment.  Water, a clear, odorless, and tasteless liquid essential for animal and plant life, has a chemical formula of Dihydrogen oxide (𝐻2𝑂). It freezes below 0 degrees centigrade and boils above 100 degrees centigrade. Water's solid state is ice, while its gaseous state is water vapor or steam. Temperature units are defined by the triple point of water, 273.16 K (0.01°C) and 611.2 Pa, where solid, liquid, and gaseous water coexist in equilibrium. Water exhibits unusual behaviors, including the formation of Figure 1. Water Molecules noncrystalline solid states like vitreous ice.  Water is a polar covalent molecule consisting of one oxygen atom and two hydrogen atoms. The oxygen atom attracts shared electrons more than the hydrogen atoms, requiring a partial negative charge (δ−) and a partial positive charge (δ+). The bent shape of the water molecule is crucial as polar O-H bonds do not cancel each other, making the molecule polar. The oxygen is the negative Figure 2. end, while the hydrogen atom area is the positive end.  Water is a polar covalent molecule consisting of one oxygen atom and two hydrogen atoms. The oxygen atom attracts shared electrons more than the hydrogen atoms, requiring a partial negative charge (δ−) and a partial positive charge (δ+). The bent shape of the water molecule is crucial as polar O-H bonds Figure 3. do not cancel each other, making the The water molecule in (a) ball and molecule polar. The oxygen is the negative stick model, (b) space filling model, (c) end, while the hydrogen atom area is the structural formula with partial charges. positive end. The molecule adopts a bent structure because of the two lone pairs of electrons on the oxygen atom. The H−O−H bond angle is about 105° , slightly smaller than the ideal 109.5° of an 𝑠𝑝³ hybridized atomic orbital. The electronic configuration for the valence electron of oxygen are 2𝑠²2𝑝⁴. Since the energy levels of 2s and 2p are close, valence electrons have characters of both s and p. The mixture is called 𝑠𝑝³ hybridization.  Polar molecules attract each other through dipole- dipole forces, with water's highly polar O-H bonds resulting in little electron density around hydrogen atoms. Hydrogen bonds, stronger than conventional dipole-dipole forces, are attracted to lone-pair electrons on adjacent oxygen atoms. These are called hydrogen bonds and are stronger than conventional dipole-dipole forces (fig 4). Each oxygen atom has two lone pairs, allowing it to form hydrogen bonds with two separate molecules. This results in an approximately tetrahedral geometry around each oxygen atom, consisting of two Figure 4. Hydrogen bond covalent bonds and two hydrogen bonds. Water molecules exhibit symmetrical properties, with two mirror planes containing all three atoms and one perpendicular to the plane passing through the H-O-H angle. When rotated 180°, the shape remains unperturbed, indicating a 2-fold rotation axis. This type of symmetry belongs to the point group C2v and consists of two symmetry elements and two mirror planes. Water is in C2v point group so it has 4 symmetry elements E, C2, σv(xz), σv'(yz). That means it will have one C2 axis of rotation that cause equivalent appearance on a 180° rotation about the axis (passing through oxygen and mid- point of the straight line joining two hydrogen). Water molecule also has two plane of symmetry one is molecular plane (passing through H—O—H) and another is passing through oxygen and reflect two hydrogen in both side.  Surface tension is the property of a liquid's surface that allows it to resist external forces due to its cohesive nature. Cohesion refers to the attraction of molecules for each other, and water molecules have strong cohesive forces due to their ability to form hydrogen bonds. Water molecules at the surface (at the water-air interface) will form hydrogen bonds with their neighbors, just like water molecules deeper within the liquid. Meanwhile, Surface tension is shared with all neighboring molecules, with those on the surface exhibiting stronger attractive forces towards their Figure 7. Molecules at the surface of nearest neighbors. This property allows water water experience a net attraction to molecules to resist external forces and maintain their other molecules in the liquid equilibrium. Water molecules cling to each other, creating a stronger bond and a layer of strongly bonded water. This surface layer, held together by surface tension, creates a barrier between the atmosphere and water. Water has the greatest surface tension of any liquid, making small objects "float" on the surface of a fluid, acting like an elastic membrane when under tension.  EXAMPLES OF SURFACE TENSION Walking on water: Small insects such as the water strider can walk on water because their weight is not enough to penetrate the surface. Floating paper clip made of steel with copper plating. The high surface tension helps the paper clip - with much higher density - float on the water. Surface Tension and Droplets: Surface tension is responsible for the shape of liquid droplets. Droplets of water tend to be pulled into a spherical shape by the cohesive forces of the surface layer. Common tent materials are rainproof due to water surface tension bridging pores, but finger contact breaks this tension, allowing rain to drip through.  EXAMPLES OF SURFACE TENSION Surface tension disinfectants: Disinfectants are usually solutions of low surface tension. This allow them to spread out on the cell walls of bacteria and disrupt them. Soaps and detergents aid in cleaning clothes by reducing water's surface tension, allowing it to more easily penetrate pores and soiled areas. Cold water is preferred for washing due to its lower surface tension and better wetting ability, but heating may be unnecessary if the detergent lowers surface tension. Why bubbles are round: The surface tension of water provides the necessary wall tension for the formation of bubbles with water. The tendency to minimize that wall tension pulls the bubbles into spherical shapes. Adhesion is the attraction between different molecules, such as water, and can be strong, allowing water to climb through capillary tubes in a beaker. This capillary action relies on adhesion and cohesion interactions. Water molecules are more strongly attracted to glass due to its polarity. The water extends highest at tube edges and dips lowest in the middle, creating a meniscus. Capillary action aids in plant nutrient transport. Water's ability to moderate temperature is due to its high-specific heat and high heat of vaporization properties. High-specific heat refers to the energy required to change temperature by 1 degree Celsius. Water molecules form hydrogen bonds, which break down, allowing them to move freely and increase temperature. Hydrogen bonds absorb and release heat, minimizing temperature changes. Water helps maintain a moderate temperature, protects living organisms, and serves as a coolant in industrial applications.  Water's high heat of vaporization and high heat of evaporation are key properties that moderate temperature. Water requires significant energy to break down hydrogen bonds and convert BOILIN EVAPORATION a gram of liquid into gas, which in turn G cools the environment. This process, particularly in humans, helps maintain body temperature homeostasis. Water's small molecular weight has a high boiling and freezing point due to its energy required to break hydrogen bonds. This slows down boiling or freezing, crucial for ecosystems. Water's high boiling and freezing points prevent drastic environmental changes, allowing sweat to cool our bodies. At cooler temperatures, the hydrogen bonds of water molecules form ice crystals. The hydrogen bonds are more stable and will maintain its crystal-like shape. Ice—the solid form of water—is less dense than water because of the hydrogen bonds being spaced out and being relatively apart. The low density is what allows icebergs to float and are the reason that only the top part of lakes are frozen. Water freezes from the top down due to a unique property of water's density at falling temperatures. Density is the mass of a unit volume of a substance, and as temperatures drop, its density increases. In lakes and rivers, ice crystals form, float to the surface, and eventually cover the bulk of the water underneath. This ice acts as insulation, retaining heat in the liquid below. In normal winters, the cold doesn't freeze all the water, allowing fish to survive until spring warms the surface and melts the ice.  Liquid Phase (Water) Water is primarily a liquid under standard conditions, unlike gaseous hydrides like hydrogen sulfide. This is because oxygen is more electronegative than surrounding elements, resulting in a partial positive and negative charge on hydrogen and oxygen atoms. This creates hydrogen bonds, which are constantly formed and broken as water molecules slide past each other. This electrical attraction, known as hydrogen bonding, pulls molecules closer together, raising the boiling point. When water is boiled, hydrogen bonds break completely, allowing water molecules to escape into the air as gas. When water freezes, it forms a crystalline structure, making ice less dense than liquid water.  Gas Phase (Water Vapor) Water is primarily a liquid under standard conditions, unlike gaseous hydrides like hydrogen sulfide. This is because oxygen is more electronegative than surrounding elements, resulting in a partial positive and negative charge on hydrogen and oxygen atoms. This creates hydrogen bonds, which are constantly formed and broken as water molecules slide past each other. This electrical attraction, known as hydrogen bonding, pulls molecules closer together, raising the boiling point. When water is boiled, hydrogen bonds break completely, allowing water molecules to escape into the air as gas. When water freezes, it forms a crystalline structure, making ice less dense than liquid water.  Water as Universal Solvent Water's polarity allows it to dissolve or dissociate many particles due to its hydrogen bonds. When a compound's negatively charged particles attract water's hydrogen atoms, it dissolves. Salt dissolves in water, forming hydration shells around the ions to maintain particle separation. Hydrogen-bonded water molecules form a cage-like structure around nonpolar molecules, with sodium and chloride ions surrounded by oxygen and hydrogen, respectively. Alkali Metal Hydrides and Water Similar to the Group 1 oxides, the hydrides of the Group 1 elements react with water to form a basic solution. In this case, however, hydrogen gas is produced with the metal hydroxide. The general reaction for alkali metal hydrides and water is given below: This reaction can be generalized to all alkali metal hydrides. Group 13 elements are not very reactive with water. In fact, boron (B) does not react at with water. One notable reaction within this group is aluminum's (Al) reaction with water. Aluminum does not appear to react with water because an outer layer of aluminum oxide (𝐴𝑙2𝑂3) solid forms and protects the rest of the metal. For the most part, Group 14 elements do not react with water. One interesting consequence of this is that tin (Sn) is often sprayed as a protective layer on iron cans to prevent the can from corroding. The pure elements in this family do not tend to react with water. Compounds of nitrogen (nitrates and nitrites) as well as nitrogen gas (N₂) dissolve in water but do not react. As mentioned earlier, many Group 1 and Group 2 oxides react with water to form metal hydroxides. The nonmetal oxides react with water to form oxoacids. Examples include phosphoric acid and sulfuric acid. Halogens react with water to form halides and hypohalides, with fluorine displaced oxygen gas, producing oxygen gas and hydrogen fluoride. Hydrogen halides form hydrohalic acids, strong acids in water, except for HF. Hydrochloric acid (HCl), a strong acid, is an example. Noble gases are odorless, colorless, nonflammable, and monotonic gases that have low chemical reactivity. The full valence electron shells of these atoms make noble gases extremely stable and unlikely to form chemical bonds because they have little tendency to gain or lose electrons. The noble gases do not react with water. Answer the following briefly. 1. Describe the composition of water. 2. Define cohesion and explain the cohesive action of water molecules. 3. Define adhesion and explain the adhesion action of water molecules 4. Why is water a polar molecule? 5. Enumerate the properties of water. 6. What is surface tension? Give 3 examples of water’s surface tension 7. Give the importance of water’s capillary action. 8. Give three importance of water having high specific heat. 9. Why does ice floats? And why does only the top part of the lakes are frozen? 10. Write the product in the following reactions with water. a. monoxides reacts with water b. peroxides reacts with water c. superoxides reacts with water d. alkali metal hydrides reacts with water e. alkali metal reacts with water f. alkaline earth metal monoxides combine with water g. alkaline earth metal combines with water h. alkaline metal hydrides react with water i. bromine dissolves in water j. chlorine dissolves in water