General Chemistry 2 Quarter 3 Module 2 PDF

Senior High School General Chemistry 2 Quarter 3 Week 2 Module 2 Properties of Liquids, The Effects of Intermolecular Forces and The Structure of Water General Chemistry 2 – Senior High School Alternative Delivery Mode Quarter 3 Week 2 Module 2: The Effects of Intermolecul...

Senior High School General Chemistry 2 Quarter 3 Week 2 Module 2 Properties of Liquids, The Effects of Intermolecular Forces and The Structure of Water General Chemistry 2 – Senior High School Alternative Delivery Mode Quarter 3 Week 2 Module 2: The Effects of Intermolecular Forces, The Properties of Liquids and The Structure of Water 2nd Edition 2021 Republic Act 8293, section 176 states that: No copyright shall subsist in any work of the Government of the Philippines. However, prior approval of the government agency or office wherein the work is created shall be necessary for exploitation of such work for profit. Such agency or office may, among other things, impose as a condition the payment of royalties. Borrowed materials (i.e., songs, stories, poems, pictures, photos, brand names, trademarks, etc.) included in this module are owned by their respective copyright holders. Every effort has been exerted to locate and seek permission to use these materials from their respective copyright owners. The publisher and authors do not represent nor claim ownership over them. Published by the Department of Education Secretary: Leonor Magtolis Briones Undersecretary: Diosdado M. San Antonio Development Team of the Module Developer / Compiler: Yvonne Lynn V. Torres, Master Teacher II, Cebu City National Science High School Language Editor: Roquesa B. Sabejon, PSDS North District VII Content Editors: Celia C. Gepitulan, Principal I, Regino Mercado Night High School Bonnie James A. Saclolo, Teacher III, Cebu City National Science High School Jocelyn C. Butanas, Master Teacher I, Talamban National High School Management Team: DR. RHEA MAR A. ANGTUD, Schools Division Superintendent DR. BERNADETTE A. SUSVILLA, Asst. Schools Division Superintendent MRS. GRECIA F. BATALUNA, CID Chief DR. RAYLENE S. MANAWATAO, EPSvr – Science MRS. VANESSA L. HARAYO, EPSvr – LRMS Printed in the Philippines by DepEd Cebu City Department of Education – Region VII Office Address: New Imus Road, Barangay Day-as, Cebu City Telephone No.: (032) 253 2559 E-mail Address: [email protected]  What I Need to Know This module was designed and written with you in mind. It is here to help you master the nature of Chemistry. The scope of this module permits it to be used in many different learning situations. The language used recognizes the diverse vocabulary level of students. The lessons are arranged to follow the standard sequence of the course. The module is consisting of three lessons, namely: Lesson 1: The Effects of Intermolecular Forces Lesson 2: The Properties of Liquids Lesson 3: The Structure of Water After going through this module, you are expected to: 1. describe three types of attraction between molecules in a liquid 2. identify five observed properties of a liquid 3. explain the concept of an intermolecular bond 4. describe the following properties of liquids, and explain the effect of intermolecular forces on these properties: surface tension, viscosity, vapor pressure, boiling point, and molar heat (STEM_GC11IMFIIIa-c-102) 5. describe the relationship between intermolecular attraction in a liquid and the properties of vapor pressure, boiling point, viscosity, and surface tension 6. predict which liquid in a pair has the higher vapor pressure, boiling point, viscosity, and surface tension 7. explain the properties of water with its molecular structure and intermolecular forces (STEM_GC11IMIIIa-c-103) 8. illustrate the bond angle and net dipole in a water molecule 9. explain the unusual physical properties of water 10. write the chemical equations for the chemical reactions of water What I Know Write the letter of the correct answer on a separate sheet of paper. 1. Which of the following is an observed general property of liquids? Liquids ______. A. are denser than gases C. are insoluble mix homogeneously B. expand and compress significantly D. have fixed shape and variable volume 2. What is the strongest intermolecular force in liquid ammonia, NH3? A. dipole forces C. hydrogen bonds B. dispersion forces D. all of the above 3. Which of the following properties has a relatively high value if the molecules in a liquid have a strong attraction for each other? A. viscosity C. surface tension B. boiling point D. all of the above 4. How many dipoles are in a water molecule? A. 0 B. 1 C. 2 D. 3 5. Which of the following explains why ice floats on water? Ice has greater __________. A. density than water C. volume than an equal mass of water B. specific heat than water D. heat of fusion and molar mass than water 6. Which of the following properties has a low value if the molecules in a liquid are strongly attracted? A. viscosity C. vapor pressure B. boiling point D. surface tension 7. What is the general relationship between the vapor pressure of a liquid and its temperature? A. direct B. doubled C. inverse D. reduced to half For questions 8-11, refer to the graph on the right side. 8. What is the estimated value of vapor pressure in mmHg of ethanol at 45°C? A. ≈90 C. ≈320 B. ≈180 D. ≈600 9. What is the estimated value of vapor pressure in mmHg of ethanol at 60°C? A. ≈90 C. ≈320 B. ≈180 D. ≈600 10. What is the estimated value of vapor pressure in mmHg of ether at 30°C? A. ≈80 C. ≈300 B. ≈200 D. ≈400 11. What is the estimated value of vapor pressure in mmHg of ether at 15°C? A. ≈80 C. ≈300 B. ≈200 D. ≈400 For questions 12-15, refer to the table given. 12-15. What is the physical state for each of the following molecules at the given temperature? 12. H2O at -10°C: A. gas B. liquid C. plasma D. solid 13. NH3 at -100°C: A. gas B. liquid C. plasma D. solid 14. H2O at 110°C: A. gas B. liquid C. plasma D. solid 15. NH3 at -50°C: A. gas B. liquid C. plasma D. solid  Lesson The Effects of Intermolecular 1 Forces What’s In The molecules of most gases are so widely separated at ordinary temperatures and pressures that they do not interact with one another significantly. The physical properties of gases are reasonably well described by the simple relationships in the previous module on Gases. In liquids and solids, the so-called condensed phases, the particles are close together so they interact much more strongly. Although the properties of liquids and solids can be described, they cannot be adequately explained by simple mathematical relationships. Table 2.1 summarizes some of the characteristics of gases, liquids and solids. Table 2.1. Some Characteristics of Solids, Liquids and Gases SOLIDS LIQUIDS GASES have definite shape (resist have no definite shape (assume have no definite shape (fill deformation) shapes of containers) containers completely) are nearly incompressible have definite volume (are only are compressible slightly compressible) usually has higher density than have high density have low density liquids are not fluid are fluid are fluid diffuse only very slowly through diffuse through other liquids diffuse rapidly solids have an ordered arrangement consist of disordered clusters of consist of extremely disordered of particles that are very close particles that are quite close particles with much empty together; particles usually have together; particles have random space between them; particles only vibrational motion motion in three dimensions have rapid, random motion in three dimensions What’s New The main use of soda ash is the manufacture of glass. Soda ash is also used to clean up hazardous spills, and hydrates of soda ash are used in chemistry laboratory experiments. Sodium carbonate, Na2CO3, is also known as soda ash and washing soda. It commonly occurs as a crystalline hydrate, which readily effloresces forming a white powder. Sodium carbonate is a white, odorless powder that absorbs moisture from the air, and is used Figure 2.1 Powdered Soda Ash as a water softener. Sodium carbonate, Na2CO3, https://independentchemical.com/blogs /what-is-sodium-carbonate-or-soda- crystallizes from aqueous solution to form three ash-used-for-20068.aspx different hydrates: sodium carbonate monohydrate (Na2CO3 H2O), sodium carbonate heptahydrate (Na2CO3 7H2O), and sodium carbonate decahydrate (Na2CO3 10H2O). Each hydrate can be decomposed by heating with predictable results, which make them suitable for routine chemistry laboratory experiments.  The manufacture of glass is one of the most important uses of sodium carbonate. This type of glass is known as “soda lime” glass. The “soda” refers to sodium carbonate, and “lime” refers to calcium carbonate, which are used in its manufacture. Soda lime glass has been the most common form of glass dating back to the Egyptians, circa 1000 B.C. Sodium carbonate is also used in the process of developing photographic film. Sodium carbonate in solution has the ability to react with metals such as zinc and aluminum while releasing hydrogen gas. It is frequently added to swimming pools in order to reduce the corrosive effects of chlorine and raise the pH. In the last 10years, the Department of Transportation has reported over 100,000 hazardous waste spills. The hazardous waste includes flammable liquids, corrosive chemicals, and poisonous materials. Hazardous waste spills of acids or bases are neutralized with soda ash and baking soda, which can then be washed down a sewer drain. What Is It PROPERTIES OF LIQUIDS Unlike gases, liquids do not respond significantly to temperature and pressure changes. Also, the mathematical relationships that apply to gases, such as the combined gas law, do not apply to liquids. Rather, when we study the liquid state, we observe the following general properties: 1. Liquids have a variable shape, but a fixed volume. The shape of a liquid conforms to the shape of its container. 2. Liquids usually flow readily. Liquids flow at different rates; for example, petroleum flows more slowly than water. 3. Liquids do not compress or expand significantly. The volume of a liquid varies very little with changes in temperature or pressure. 4. Liquids have a high density compared to gases. Gases and liquids are both fluids; that is, the shape is not fixed and individual particles are free to move throughout the container. However, the liquid state is about 1000 times denser than the gaseous state because particles in a liquid are closer together. For example, the density of water is 1.00 g/mL, whereas the density of air at sea level is about 0.001 g/mL. 5. Liquids that are soluble mix homogeneously. Liquids diffuse more slowly than gases. However, liquids that are soluble eventually form a homogeneous mixture. For example, when food coloring is added to water, the liquids diffuse slowly and mix uniformly. THE INTERMOLECULAR BOND CONCEPT The Internet is an international network for computers, whereas an Intranet is a localized network; and highways are designated interstate (between states) or intrastate (in state). Similarly, an intermolecular bond indicates an attraction between molecules, whereas an intramolecular bond is between atoms in a molecule. Some properties of liquids, such as vapor pressure, are determined by the strength of attraction between molecules. This attraction is called an intermolecular bond, and it is much weaker than an intramolecular bond between atoms. The three types of intermolecular attraction are based on temporary dipoles, permanent dipoles, and hydrogen bonds.  Temporary Dipole Attraction In molecules, positive and negative charges are concentrated in different regions of individual molecules. These two charged regions are created by an uneven distribution of electrons in the molecule. A molecule having regions of positive and negative charge is said to possess a dipole. Let’s first consider temporary dipole attraction. Even though atoms in a molecule may share electrons equally, the electrons are constantly shifting about. This shifting about of electrons produces regions in the molecule that are temporarily “electron rich” and slightly negative. Simultaneously, another region of the molecule is temporarily “electron poor” and slightly positive. A negative region in one molecule has a weak attraction for a positive region in another molecule. This temporary attraction between molecules is referred to as a dispersion force. Although dispersion forces last for only brief periods of time, they occur frequently between molecules. Figure 2.2 illustrates temporary intermolecular dispersion forces between the positive end of a molecule (∂+), and the negative end of a molecule (∂-). Figure 2.2 Intermolecular Dispersion Forces (a) Two molecules are shown. (b) The molecule on the left forms a temporary dipole, which can induce a dipole in the molecule on the right. (c) The two molecules are temporarily attracted to each other. In turn, these molecules induce temporary dipole attractions in the surrounding molecules in the liquid. Permanent Dipoles and Hydrogen Bonds Atoms of different elements vary in their attraction for electrons. This gives rise to regions of positive and negative charge in a molecule. As a result, similar to magnets, individual molecules are attracted to each other. In contrast to temporary dipole attraction, permanent dipole attraction operates continuously. That is, a permanent dipole force operates between molecules as shown in Figure 2.3. Figure 2.3 Intermolecular Dipole Forces (a) A dipole force results from a dipole–dipole attraction between two molecules. (b) Dipole forces between several molecules in a liquid is shown. When a hydrogen atom is bonded to a fluorine atom, an oxygen atom or a nitrogen atom in a molecule, an especially strong dipole result. This strong dipole produces an attraction between molecules that is typically about 10% of the strength of an intramolecular bond. This special type of permanent dipole attraction is called a hydrogen bond (Figure 2.4). Hydrogen bonds are important in living organisms where they maintain the structure of protein molecules, and the double-helix structure of DNA molecules.  Figure 2.4 Intermolecular Hydrogen Bonds Water molecules form intermolecular hydrogen bonds. Notice that the hydrogen atom is attracted to the nonbonding electrons on the highly electronegative oxygen atom. Example Exercise 2.1: INTERMOLECULAR ATTRACTION If molecules in a liquid have a permanent dipole, what is the strongest type of intermolecular attraction? Answer: In a liquid, intermolecular attraction is the result of both permanent and temporary dipoles. Molecules that contain either H¬O or H¬N bonds have the strongest type of intermolecular attraction, that is, hydrogen bonds. Water, H 2O, and ammonia, NH3, are examples of liquids with hydrogen bonds. Lesson The Properties of Liquids 2 PROPERTIES OF LIQUIDS In the previous module, we introduced the kinetic theory of gases to explain the behavior of gases. Now, we will extend this theory to explain the properties of liquids. According to the kinetic theory the attraction between gas molecules is negligible. This is not the case for liquids. Molecules in the liquid state are in contact with each other, and their attraction restricts their movement. Individual molecules do have enough energy to move about one another; that is, a liquid is free to flow. The liquid state and the gaseous state are analogous to honeybees swarming in a hive (liquid state), and individual bees flying off to gather pollen (gaseous state). Now let’s consider some properties of liquids. Vapor Pressure The kinetic theory relates the average energy of molecules to temperature. The higher the temperature, the greater the kinetic molecular energy. However, not all molecules at the same temperature have identical energies. Some are more energetic than others. At the surface of a liquid, for example, some molecules have enough energy to completely escape the attraction of neighboring molecules. The molecules that escape enter the gaseous state, which is referred to as vapor. This process is called vaporization. In the reverse process, some molecules in the vapor return to the liquid. This process is called condensation.  When the rates of vaporization and condensation are equal, the pressure exerted by the gas molecules above a liquid is called the vapor pressure. However, the vapor pressure above a liquid depends on the attraction between molecules in the liquid. Water molecules have a strong attraction for each other, and ethyl ether molecules have a relatively weak attraction. Because of the lesser attraction between molecules, ether molecules escape from the liquid state more readily than water molecules. Therefore, the vapor pressure of ether is greater than that of water at the same temperature (Figure 2.5). Figure 2.5 Vapor Pressure of Water and Ether (a) At 0 °C neither water nor ether has sufficient vapor pressure to affect the balloons. (b) At 35 °C the vapor pressure of water is still low; however, the vapor pressure of ether is considerable and inflates the balloon. Table 2.2 compares the attraction between molecules, that is, intermolecular attraction, and the vapor pressure for a few selected liquids. In general, as the attraction between molecules increases, the vapor pressure decreases. In Table 2.2 we see that propionic acid and butyl alcohol both have a strong intermolecular attraction. Thus, their vapor pressures at 20 °C are quite low. Conversely, propyl chloride and ethyl ether each has a weak intermolecular attraction. Thus, their vapor pressures are considerably higher. When comparing vapor pressure values, it is necessary to choose two liquids that have approximately the same molar mass. Note that in these comparisons, each liquid, except water, has an approximate molar mass of 74g/mol. Table 2.2 Boiling Point As the temperature of a liquid increases, its vapor pressure increases. At 30 °C the vapor pressure of water is about 30 mm Hg, and at 60 °C it is  150 mm Hg. Figure 2.6 shows the relationship between vapor pressure and temperature for ether, ethanol, and water. Figure 2.6 Boiling Points of Some Common Liquids The vapor pressure of water equals 760 mm Hg at 100 °C. Thus, at 100 °C the vapor pressure of water equals the standard atmospheric pressure (760 mm Hg), and water begins to boil. A liquid begins to boil when the pressure of the vapor above the liquid equals the pressure of the atmosphere. Thus, we define the normal boiling point (symbol Bp) as the temperature at which the vapor pressure equals standard atmospheric pressure. Accordingly, liquids that have high boiling points must have low vapor pressures. The following example exercise illustrates the determination of boiling points from vapor pressure data. Example Exercise 2.2: BOILING POINT PREDICTIONS Using figure 2.6, determine the boiling points of the following: 1. Ether 2. Ethanol 3. Water Answers: The normal boiling point of a liquid is the temperature at which the vapor pressure equals standard atmospheric pressure, that is, 760 mm Hg. From the graph, we find that the vapor pressure of Viscosity (1) ETHER is 760 mm Hg at about 35 °C Some liquids are easier to pour than others. Water pours easily, (2) ETHANOL is 760 mm Hg at about 78 °C whereas honey does not. The resistance of a liquid to flow is a property called is theis (3) WATER viscosity. Viscosity 760 of result mman Hg at about attraction 100 °C between molecules. It is also affected by factors such as the size and shape of the molecules. In principle, the greater the attraction between molecules, the higher the viscosity. Table 2.3 compares the attraction between molecules and the viscosity for a few selected liquids. Table 2.3 In Table 2.3, we see that propionic acid and butyl alcohol have a strong intermolecular attraction and that the viscosity of both is greater than that of  water. We also see that propyl chloride and ethyl ether have a weak attraction between molecules and that the viscosity of both is much lower than that of water. Honey is an example of a viscous liquid. We can therefore predict that there is a strong attraction between molecules in honey. Surface Tension At some time, you have probably noticed a small insect floating on water. For an insect or any object to sink in a liquid, it has to break through the surface. But the molecules on the surface of a liquid resist being pushed apart. The attraction between the surface molecules in a liquid is called surface tension. There are other factors to consider, but in general the greater the intermolecular attraction, the higher the surface tension. Table 2.4 compares the intermolecular attraction and surface tension for a few selected liquids. Table 2.4 Corwin, C. H. (2018). Introductory Chemistry Concepts and Critical Thinking 8th ed. USA: Prentice Education, Inc. Figure 2.7 Surface Tension Water has a high surface tension owing to hydrogen bonds, and this allows the insect to “walk” on water. We all know that rain forms drop as it falls. In fact, when we spray any liquid, it forms drops, and each drop has the shape of a small sphere. Drops of liquid are spherical because surface tension causes them to have the smallest possible surface area, and that area corresponds to a spherical droplet. Table 2.4 shows that water has an unusually high surface tension.  Example Exercise 2.3: PHYSICAL PROPERTY PREDICTIONS OF LIQUIDS IN RELATION TO INTERMOLECULAR FORCES Consider the following properties of liquids. State whether the value for each property is high or low for a liquid with a strong intermolecular attraction: (a) vapor pressure (c) viscosity (b) boiling point (d) surface tension Answers: For a liquid having a strong attraction between molecules, properties (b), (c), and (d) are generally HIGH; property (a) is LOW. (a) Molecular attraction slows vaporization. Therefore, vapor pressure is low for liquids with a strong intermolecular attraction. (b) Attraction between molecules inhibits boiling. Thus, the boiling point is high for liquids with a strong intermolecular attraction. (c) Molecular attraction increases the resistance of a liquid to flow. Viscosity is high for liquids with a strong intermolecular attraction. (d) Attraction between molecules causes a drop of liquid to form a sphere. Surface tension is high for liquids with a strong intermolecular attraction. Lesson The Structure of Water 3 STRUCTURE OF WATER We learned in Lesson 2 that the boiling point and surface tension of water are unusually high. We also saw that water has a strong intermolecular attraction because of hydrogen bonding. To understand these properties more completely, let’s review the water molecule. Specifically, let’s examine the structural formula, bond angle, and net dipole for a water molecule. Structural Formula and Bond Angle The structural formula for a molecule uses dashes to represent bonds between atoms. We will draw the water molecule with the two hydrogen atoms at an angle to each other. Experimental evidence shows that the angle between the two hydrogen atoms is 104.5°. The angle formed by the central atom and two attached atoms is referred to as the bond angle. BOND ANGLE Dipoles and Net Dipole In a water molecule, each of the two bonds is a dipole. That is, the oxygen atom is slightly negative and each hydrogen atom is slightly positive. We can indicate this using sigma notation (δ+ and δ-). Slightly negative Slightly positive  Notice that a water molecule has two dipoles, and the central oxygen atom is pulling electrons toward the O atom. The two dipoles create a single dipole passing through the center of the molecule. The single, overall dipole for a molecule having two or more dipoles is called the net dipole. The net dipole produces a negative end and a positive end in the water molecule. The negative end of the molecule is indicated by the tip of the arrow. The positive end is indicated by the plus sign on the opposite end of the net dipole arrow. The positive and negative ends of different water molecules form hydrogen bonds. This strong intermolecular attraction between water molecules explains water’s unusual properties, including a high boiling point and high surface tension. PHYSICAL PROPERTIES OF WATER Water is a colorless, odorless, tasteless liquid, and a powerful solvent. At room temperature water has the highest specific heat, heat of fusion (except for ammonia), and heat of vaporization of any liquid. Density Generally, a substance in the solid state has a higher density than one in the liquid state. Therefore, we would predict that the density of ice is greater than that of water. But we know that ice floats in water. That is, the solid form of water is less dense than the liquid form. The reason solid ice is less dense than liquid water relates to hydrogen bonding. Figure 2.8 illustrates three-dimensional hydrogen bonding in water. Corwin, C. H. (2018). Introductory Chemistry Concepts and Critical Thinking 8th ed. USA: Prentice Education, Inc. Figure 2.8 Hydrogen Bonding Each water molecule is attracted to four other water molecules. These intermolecular hydrogen bonds are about 50% longer than an ordinary covalent bond. Because a hydrogen bond is longer, it is weaker and requires much less energy to break. When water freezes to ice, the hydrogen bonds produce a three- dimensional crystal. Figure 2.9 illustrates the structure of an ice crystal. Because of the arrangement of water molecules, however, the crystal has holes. These holes create a volume for ice that is greater than that for an equal mass of water. Thus, the density of solid ice is less than that of liquid water.  At 0 °C, the density of ice is 0.917 g/mL, and the density of water is 1.00 g/mL. Corwin, C. H. (2018). Introductory Chemistry Concepts and Critical Thinking 8th ed. USA: Prentice Education, Inc. Figure 2.9 Structure of Ice Crystals Water molecules hydrogen bond to form six member rings. The rings in turn hydrogen bond to other rings, producing large, three dimensional crystalline structures. Melting and Boiling Points Water has an unusually high melting point and boiling point for a small molecule. To see how unusual these properties are, compare them with those of some hydrogen compounds of Group VIA/16 as outlined in Table 2.5. Table 2.5 If we ignore water, we see a clear trend in the melting and boiling points of Group VIA/16 hydrogen compounds. First, notice the increase in molar mass for H2S through H2Te. Next, notice that the values for the melting point and the boiling point increase simultaneously. As with density, the properties of water are unusual because of hydrogen bonding. Hydrogen bonding produces a strong intermolecular attraction that resists the movement of molecules. Therefore, a higher temperature is needed to melt ice and to boil water. Figure 2.10 illustrates the melting and boiling points of Group VIA/16 hydrogen compounds. Figure 2.10 Melting Point and Boiling Point of Group VIA/16 Hydrogen Compounds Notice the systematic trend in melting point and boiling point as the molar mass increases. Water is a striking exception because of strong intermolecular hydrogen bonds.  Example Exercise 2.4: PHYSICAL PROPERTY PREDICTIONS OF LIQUIDS IN RELATION TO MELTING AND BOILING POINT Predict which compound in each of the following pairs has the higher boiling point: (a) NH3 or PH3 (b) PH3 or AsH3 Answers: Ammonia, NH3, molecules can form hydrogen bond, while PH3 and AsH3 cannot. (a) Ammonia, NH3, has a higher boiling point than PH3. (b) AsH3 has a higher boiling point than PH3 because it has a greater molar mass. Heats of Fusion and Vaporization Water also has surprisingly high values for heat of fusion and heat of vaporization. This is illustrated in Table 2.5, excluding water, we notice that as the molar mass of H2S through H2Te increases, the values for the heat of fusion and heat of vaporization increase. The explanation for this trend is that as the molecular size increases, the attractive forces increase slightly. Therefore, more energy is required to melt a solid or vaporize a liquid. The unusually high values for water are due to hydrogen bonding. CHEMICAL PROPERTIES OF WATER Previously, we studied five basic types of chemical reactions. Water is usually the solvent for these chemical reactions, although water can also be a reactant. One example is the passing of an electric current through water, which decomposes H2O into hydrogen and oxygen gases. This process is called the electrolysis of water. From the balanced chemical equation, we notice that two volumes of hydrogen are produced for every volume of oxygen. One of the five basic types of reactions is replacement reaction. In this reaction an active metal (Li, Na, K, Ca, Sr, or Ba) reacts directly with water to give a metal hydroxide and hydrogen gas. These reactions occur rapidly at room temperature. For example, potassium metal reacts violently with water as follows: Corwin, C. H. (2018). Introductory Chemistry Concepts and Critical Thinking 8th ed. USA: Prentice Education, Inc. Figure 2.11 Alkali Metals in Water The reaction of Li, Na, and K in water (left to right) produces hydrogen gas, which is flammable. The oxides of many metals can react with water to yield a metal hydroxide. Hydroxide compounds are said to be basic, or alkaline. A metal oxide reacts with water to yield a basic solution, so a metal oxide is referred to as a basic oxide. For example, calcium oxide reacts with water as follows: The oxides of most nonmetals react with water to yield an acidic solution. A nonmetal oxide reacts with water to yield an acid, so a nonmetal oxide is referred to as an acidic oxide. For example, carbon dioxide reacts with water as follows: Reactions that Produce Water Water is produced by several types of reactions. The simplest reaction is the formation of water directly from hydrogen and oxygen. In this reaction, hydrogen and oxygen gases react to give H2O. The reaction takes place very slowly at room temperature but explosively if exposed to a flame or spark. From the balanced chemical equation, we note that two volumes of hydrogen react with one volume of oxygen. Another reaction that produces water is the combustion of hydrocarbons. Hydrocarbons are organic compounds containing hydrogen and carbon. They burn in oxygen to give carbon dioxide and water. For example, propane, C3H8, undergoes combustion as follows: Organic compounds containing hydrogen and oxygen also undergo combustion to give carbon dioxide and water. Ethanol, C2H5OH, for example, is currently blended with gasoline to produce gasohol. It undergoes combustion to give carbon dioxide and water as follows: Recall that neutralization reactions also produce water. An acid neutralizes a base to produce an aqueous salt and water. For example, sulfuric acid, H2SO4, reacts with aqueous sodium hydroxide, NaOH, to produce sodium sulfate and water. The decomposition of a hydrate compound also produces water. A hydrate is a crystalline compound that contains a specific number of water molecules. Gypsum is a hydrate of calcium sulfate, CaSO4. The formula CaSO4 2H2O indicates that two water molecules are attached to each CaSO4 formula unit. Heating a hydrate releases water from the compound. For example, heat decomposes gypsum to give CaSO4 and two molecules of water. Thus, What’s More Direction: Answer the following questions on a separate sheet of paper. 1. Which of the following liquids has the stronger intermolecular attraction between molecules, CH3 – CH2 – OH or CH3 – O – CH3? Explain your answer. 2. Which of the following liquids has the higher boiling point, CH 3 – CH2 – OH or CH3 – O – CH3? Explain your answer. 3. The intermolecular attraction is greater in isopropyl alcohol, C 3H7OH, than in pentane, C5H12. Predict which liquid has the higher value for each of the following: a. vapor pressure c. viscosity b. boiling point d. surface tension  What I Have Learned Copy and fill in the blanks with the correct term(s). The ___(1)___ state has a variable shape but a fixed volume. Liquids usually flow readily but do not compress or expand as do gases. The densities of liquids vary but are approximately 1000 times greater than the densities of gases. Liquids mix and diffuse uniformly in a container, similar to gases. There are three basic types of intermolecular attraction: dispersion forces, dipole forces, and hydrogen bonds. A ___(2)___ has the weakest attraction and results from temporary dipoles in molecules. A ___(3)___ has a stronger attraction and results from permanent dipoles in molecules. A ___(4)___ exerts the strongest intermolecular attraction, and occurs between molecules having H¬O, or H¬N bonds. When the ___(5)___ of a liquid equals the atmospheric pressure, the liquid is at its ___(6)___. The normal boiling point of a liquid is the temperature at which the vapor pressure is 760 mm Hg. Liquids have a resistance to flow, and this property is called ___(7)___. The attraction between molecules at the surface of a liquid is called ___(8)___. Each of these properties is affected by the degree of attraction between molecules in the liquid. If the attraction is low, the vapor pressure is high. Conversely, if the attraction is high, the values for the boiling point, viscosity, and surface tension are also high. Water has unusual properties because of the two O¬H bonds separated by a ___(9)___ of 104.5°. The oxygen atom has a partial negative charge, and each hydrogen atom has a partial positive charge. These two dipoles create an overall ___(10)___ for a water molecule. Water is classified as ___(11)___, or ___(12)___, depending on the cations and anions present. Water can be boiled and collected to give ___(13)___, or passed through an ion-exchange resin to give pure ___(14)___. ___(15)___ between water molecules explain why water has extraordinarily high values for boiling point, viscosity, and surface tension. Hydrogen bonding also explains why the density of ice is less than that of water. For a ___(16)___, water has an unusually high melting point, boiling point, heat of fusion, and heat of vaporization. Water undergoes the following chemical reactions: (1) An electric current decomposes water into hydrogen and oxygen gases by ___(17)___. (2) The active metals of Groups IA/1 and IIA/2 react with water to give a ___(18)___ and hydrogen gas. (3) A ___(19)___ reacts with water to give a metal hydroxide. (4) A ___(20)___ combines with water to yield an acidic solution. What I Can Do Answer the following questions briefly. Use a separate sheet as your answer sheet. 1. Why does the paper clip float on water though its density is much greater than the density of water? 2. Which of the following has the strongest intermolecular attraction? Explain your answer. a. temporary dipole c. hydrogen bond b. permanent dipole 3. What happens to the cap of your plastic bottle filled with water when placed inside the freezer? Why does this take place? 4. What is the difference between bottled water and tap water?  Assessment Write the letter of the correct answer on a separate sheet. 1. Which of the following is NOT a general property of liquids? A. flow readily C. expand significantly B. variable shape D. less dense than gases 2. Which of the following properties has a high value if the molecules in a liquid are weakly attracted? A. boiling point C. vapor pressure B. surface tension D. viscosity 3. What is the general relationship between the vapor pressure of a liquid and its boiling point? A. direct B. doubled C. inverse D. reduced to half 4. What is the observed bond angle in a water molecule? A. 45° B. 90° C. 104.5° D. 180° 5. What intermolecular force acts on the formation of water droplets? A. dipole-dipole C. permanent dipole B. hydrogen bonding D. temporary dipole 6. Which of the following has a CORRECT set of arrangement in order of increasing boiling point? A. CH4 < C2H6 < C3H8 C. C3H8 < CH4 < C2H6 B. CH4 < C3H8 < C2H6 D. C3H8 < C2H6 < CH4 For questions 7-8, refer to the illustration on viscosity given. 7. Which of the oils given has the highest viscosity? A. 20 C. 40 B. 30 D. 50 8. Which is the CORRECT set of arrangement in order of decreasing viscosity? A. 20 > 30 > 40 > 50 B. 20 > 30 > 50 > 20 C. 30 > 50 > 20 > 30 *Note: SAE stands for Society of Automotive Engineers. They use this scale to determine the viscosity of oil under certain ambient D. 50 > 40 > 30 > 20 temperature. For questions 9-12, refer to the table given. Indicate the physical state for each of the following molecules at the given temperature. 9. Ne at -225°C: A. gas B. liquid C. plasma D. solid 10. Ne at -255°C: A. gas B. liquid C. plasma D. solid 11. Ar at -175°C: A. gas B. liquid C. plasma D. solid 12. Ar at -200°C: A. gas B. liquid C. plasma D. solid 13. Which of the following decreases as the molar mass of Group VIA/16 hydrogen compounds increases? A. boiling point C. melting point B. heat of fusion D. all of the above 14. Which of the following liquids has the highest dispersion force? A. C5H12 C. CH3CH2CH2¬Cl B. CH3¬OH D. CH3¬O¬CH3 15. Which of the following liquids has the strongest intermolecular attraction due to its hydrogen bond? A. C5H12 C. CH3¬O¬CH3 B. CH3¬OH D. CH3CH2CH2¬Cl References Corwin, C. H. (2018). Introductory Chemistry Concepts and Critical Thinking 8th ed. USA: Prentice Education, Inc. Guzman, D. F. et. al. (2012). Discover Science: Chemistry. Philippines: Diwa Learning Systems, Inc. Whitten, K. W., et. al. (2005). General Chemistry 7th ed. Brooks/Cole. Thomson Learning Asian Edition. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Supplemental_Modules_(Org anic_Chemistry)/Properties_of_Liquids_and_Solids Answer Key c. C3H7OH b. C3H7OH 3. a. C5H12 3. because of its H bond CH3 – CH2 – OH 2. 2. because of its H bond 1. 1. CH3 – CH2 – OH What’s More For inquiries or feedback, please write or call: Department of Education - Bureau of Learning Resources (DepEd-BLR) Ground Floor, Bonifacio Bldg., DepEd Complex Meralco Avenue, Pasig City, Philippines 1600 Telefax: (632) 8634-1072; 8634-1054; 8631-4985 Email Address: [email protected] * [email protected]