FINAL EXAM CHEM 219 EXAM | QUESTIONS & ANSWERS (VERIFIED) | LATEST UPDATE | GRADED A+

1 FINAL EXAM CHEM 219 EXAM | QUESTIONS & ANSWERS (VERIFIED) | LATEST UPDATE | GRADED A+ The speed of a wave (c) is the product of its frequency (ν) and wavelength (λ). Correct Answer: E = hv = h x c / λ nm to m or m to nm Correct Answer: 1 m / 10^9 nm or 10^9 nm / 1 m What is the maximum number of electrons that can have the quantum numbers n = 3, ℓ = 2, mℓ = -2? Correct Answer: The Pauli exclusion principle states that no two electrons in a given atom can share the same set of four quantum numbers (n, ℓ, mℓ, ms). This set of quantum numbers contains three quantum numbers, with the only missing quantum number being ms, which can take on the values +½ and -½. Therefore, this set of three 2 quantum numbers represents a single atomic orbital, which can contain two unique electrons: one with ms = +½ and one with ms = -½. An exothermic reaction causes the surroundings to Correct Answer: An exothermic reaction transfers energy from the system to the surroundings. That tells us the surroundings will get warmer. A theory is another word for a(n) _________. Correct Answer: A theory or model is a well established explanation of a phenomenon based on a series of facts and a body of evidence. What is the definition of a natural law? Correct Answer: A scientific law summarizes an observable behavior. The skeletal structure of a complex organic molecule is shown below. Determine the number of sigma (σ) and pi (π) bonds in the molecule. Correct Answer: Remember a single bond = 1 σ; a double bond = 1 σ + 1 π; a triple bond = 1 σ + 2 π. This molecule contains 6 double bonds, so there are 6σ and 6π. There are 28 single bonds, so there are 28 σ. This is a total 34σ and 6π. strontium phosphate Correct Answer: Sr₃(PO₄)₂ 3 Which of the following statements is true? Correct Answer: One driving force in the vaporization of a liquid is an increase in disorder (entropy). Gas molecules are more disordered than liquid molecules. Adding a non-volatile solute to a liquid also increases the disorder of the liquid molecules, so the difference in disorder between the liquid and gas phases is not as great as with a pure substance. Therefore the tendency to vaporize is not as great for the solution as it is for the pure liquid, resulting in a lower vapor pressure for the solution. Which of the following aqueous solutions would have the highest boiling point? A) 1.0 m NaNO3 B) 1.0 m HF C) 1.0 m C₆H₁₂O₆ D) 1.0 m CaCl2 Correct Answer: The dissolved solute will raise the boiling point. The more "things" that are dissolved (ions or molecules), the higher the boiling point will be. The CaCl₂ will break up into one Ca²⁺ ion and two Cl⁻ ions and there will be a concentration of 3.0 m of "things" in solution. The other choices will have fewer "things" in solution and will raise the boiling point less. Which one of the following aqueous solutions would have the highest freezing point? A) 1.0 m NaNO3 4 B) 2.0 m CH3OH C) 1.0 m C₆H₁₂O₆ D) 1.0 m CaCl2 Correct Answer: The dissolved solute will lower the freezing point. The more "things" that are dissolved (ions or molecules), the lower the freezing point will be. Since C₆H₁₂O₆ is a molecule, it will not break apart and there will only be a concentration of 1.0 m of molecules in solution. It will lower the freezing point less than all the other choices. There will be fewer "things" in solution and this will lower the freezing point less than the other choices. isoelectronic ions Correct Answer: ions containing the same number of electrons Which of the following bonds is the most polar? Correct Answer: Elements that are located far away from each other on the periodic table have larger electronegativity differences and therefore make more polar bonds. Of all the element pairs listed, Rb and Br are the farthest apart. Three blocks of the same shape and size are placed in front of you. Block A has a mass of 3.0 g, block B is 5.0 g, and block C is 10.0 g. Which has the higher density? Correct Answer: Density is the ratio of mass to volume. Since the volume is constant between all the blocks, then the block with the highest mass will have the highest density. 5 Density equation Correct Answer: mass/volume dRT = PM The solubility of a gas in a liquid generally A) increases with increasing temperature. B) increases with decreasing temperature. C) increases with increasing pressure. D) both (a) and (c). E) both (b) and (c). Correct Answer: E) both (b) and (c) Which of the following properties, in general, increase as we move left to right across a period in the periodic table? 1. atomic radius 2. ionization energy 3. metallic character A) 1 only B) 2 only 6 C) 3 only D) 1 and 2 only E) 2 and 3 only Correct Answer: B) 2 only All the following statements concerning a sample of oxygen gas at 1.00 atm pressure are true EXCEPT A) the molecules are in constant rapid random motion. B) the pressure exerted by gaseous oxygen is due to the impact of the molecules with the walls of the container. C) the average kinetic energy of the gaseous oxygen is inversely proportional to the absolute temperature of the gas. D) collisions between the gaseous molecules are elastic. E) the volume occupied by the oxygen molecules is negligible compared with the size of the container. Correct Answer: C) the average kinetic energy of the gaseous oxygen is inversely proportional to the absolute temperature of the gas. A bond in which an electron pair is unequally shared by two atoms is A) ionic. B) polar covalent. 7 C) nonpolar covalent. D) coordinate covalent. E) dipolar. Correct Answer: B) polar covalent. Which of the following statements is (are) true? 1. An excited atom can return to a higher energy level by emitting light energy. 2. An atom can be excited to a higher energy level by absorption of light energy. 3. The frequency and wavelength of light are inversely proportional. A) 1 only B) 2 only C) 1 and 3 only D) 2 and 3 only E) 1, 2, and 3 Correct Answer: D) 2 and 3 only Solvent Correct Answer: A liquid substance capable of dissolving other substances Solute Correct Answer: A substance that is dissolved in a solution. 8 Solution Correct Answer: A homogeneous mixture that forms when one substance dissolves another. The measure of the attraction that an atom has for the electrons in a chemical bond is called A) electron affinity. B) ionization energy. C) electronegativity. D) hybridization. E) London forces. Correct Answer: C) electronegativity. Avogadro's Law Correct Answer: equal volumes of gases at the same temperature and pressure contain equal numbers of molecules Boyle's Law Correct Answer: Boyle's Law states that at constant temperature and moles, pressure and volume are inversely proportional. Mathematically this is written as: PV = PV 9 Gay-Lussac's Law Correct Answer: the pressure of a gas is directly proportional to the Kelvin temperature if the volume is constant Charles' Law Correct Answer: the law that states that for a fixed amount of gas at a constant pressure, the volume of the gas increases as the temperature of the gas increases and the volume of the gas decreases as the temperature of the gas decreases Combined Gas Law Correct Answer: the relationship between the pressure, volume, and temperature of a fixed amount of gas Ideal Gas Law Correct Answer: PV=nRT R=.08206 If 5.00 g of Gas A and 5.00 g of Gas B are mixed in the same container, and the partial pressure of Gas B is determined to be twice that of Gas A, what do we know about the gases? Correct Answer: If Gas A has half the partial pressure of Gas B, this indicates that there are fewer moles of it at the same mass, and therefore Gas A has twice the molar mass of Gas B 10 mol fraction and partial pressure Correct Answer: the formula for both Amonton's Law Correct Answer: if the volume of a gas is held constant, increasing the temperature of the gas increases its pressure. Boyle's Law in terms of KE Correct Answer: Volume decreased, wall area decreased = increased pressure Avagadro's Law in terms of KE Correct Answer: Container pressure constant, more gas molecules added = increased volume Dalton's Law Correct Answer: The total pressure of a mixture of gases is the sum of the individual pressures (Ptotal=P1+P2+P3...) The kinetic energy (KE) of a particle of mass (m) and speed (u) is given by Correct Answer: KE = 1/2 mu^2 11 The KE avg of a collection of gas molecules is also directly proportional to the temperature of the gas and may be described by the equation Correct Answer: KEavg = 3/2 RT Kinetic Molecular Theory Correct Answer: The Kinetic Molecular Theory states: ⋅⋅There is no attraction between the gas particles. ⋅⋅The volume available to the gas particles is equal to the volume of the container. ⋅⋅The measured pressure is from collisions of the gas particles with the walls of the container. ⋅⋅The average kinetic energy is proportional to the temperature of the system. Which of the following gas samples have the greatest average molecular speed at 25°C? Correct Answer: Speed of individual gas molecules is inversely proportional to the molar mass. CH₄ has a molar mass of just over 16 g/mol and is the smallest of the gases listed. Therefore it has the fastest molecular speed. What is the difference between effusion and diffusion? Correct Answer: Effusion is through a pinhole, and diffusion is through open space. 12 Under what conditions are gases most likely to behave ideally? Correct Answer: Gases are more likely to behave as ideal gases at low pressures and high temperatures. Particles are moving faster and are farther apart, therefore they are less likely to interact with each other The phrase 'like dissolves like' refers to Correct Answer: "Like dissolves like" refers to the fact that polar molecules dissolve polar molecules, which both have polar and perhaps hydrogen bonding intermolecular forces, while nonpolar molecules dissolve nonpolar molecules, which generally only have dispersion intermolecular forces. Which of the following factors affect the solubility of a gas in a liquid solvent? l. Pressure II. Temperature III. Identity of gas Correct Answer: The solubility of a gas in a liquid solvent is dependent on the nature of the gas, the temperature and the pressure. Generally, the solubility of a gas in a liquid solvent increases with lower temperatures and high pressure. Forming solution A from liquid B and liquid C is endothermic. Increasing the pressure above the solution will Correct Answer: Since the solution does not contain any gases, and since liquids are incompressible, then a change in pressure will have no effect on the solution process. 13 Which of the following statements is true about the solubility of N₂ (g) in CH₃OH (l)? Correct Answer: Henry's Law states that the higher the partial pressure of the gas, the more soluble it will be in the solvent. This is because there are more molecules of the solute available to dissolve in the solvent. Hypertonic Correct Answer: A solution containing a higher concentration of solutes than inside a red blood cell Isotonic Correct Answer: A solution that matches the concentration of solutes in cells Hypotonic Correct Answer: A solution that contains a lower concentration of solutes than inside the cell Henry's Law Correct Answer: the solubility of a gas in a liquid is directly proportional to the partial pressure of that gas on the surface of the liquid The predicted van't Hoff factor for a calcium chloride solution, CaCl₂(aq), is 14 Correct Answer: When the strong electrolyte CaCl₂ dissolves, it breaks up into one Ca²⁺ and two Cl⁻ ions. That gives a van't Hoff factor of 3. At a particular temperature, the solubility of H₂ in water is 0.140 M when the partial pressure is 1.20 atm. What partial pressure (in atm) of H₂ would give a solubility of 4.95 M? Correct Answer: 42.4 atm C = kP -- c12/c1 = p2/p1 The Henry's law constant at 25.0 °C for N₂ in water is 0.00061 M/atm. What is the solubility of N₂, in molarity units, in 1.0 L of water when the partial pressure of N₂ is 2.4 atm? Correct Answer: 0.0015 M C= kP k= M/atm p= atm C = M (NH₄)₂SO₄ has a van't Hoff factor of i = 2.3. What is the concentration of particles in a 0.7801 M solution of (NH₄)₂SO₄? Correct Answer: 1.8 M 2.3 x 0.7801 = 1.8 15 M = ( i ) x ( M ) What is the molarity of ions in a 0.425 M solution of Li₂SO₄ assuming the compound dissociates completely? Correct Answer: 1.28 M When an ionic compound dissociates completely, the ions are separated from each other and surrounded by water molecules. In this compound, the two lithium ions separate from the sulfate ion 3 × 0.587 M = 1.76 m A solution is made by dissolving 2.5 mg sodium fluoride (NaF) in 1.5 L of water at 20.0°C. What is the fluoride ion concentration in ppm of the resulting solution, given that NaF is 45.0% fluoride ion by mass, and the density of water of 1.00 kg/L? Correct Answer: 2.5 x 45/100 = 1.125mg weight of ion / weight of water = ppm so, 1.5L = 1.5 Kg 1.125mg / 1.5 kg = 0.75 A solution is made using 175.7 g of hexane (MM = 86.18 g/mol) and 200.0 g of octane (MM = 114.2 g/mol). What is the molality of the hexane in the solution? Correct Answer: m = (W g of solute / Molar mass of solute) (1000 / W g of solvent) 16 (175.7g / 86.18g/mol) ( 1000 / 200g) = 10.19m A solution is made using 163.7 g of dimethyl ether (MM = 46.07 g/mol) and 90.0 g of methanol (MM = 32.04 g/mol). What is the mole fraction of the dimethyl ether in the solution? Correct Answer: find mol of dim & methanol dim mol / dim mol + methanol = mol fraction Which of the following aqueous solutions would have the highest vapor pressure? Correct Answer: According to Raoult's Law, the vapor pressure of a solution is proportional to the mole fraction of solvent, and therefore, inversely proportional to the total solute concentration. So, the lowest molarity of ions will have the highest vapor pressure. Since ionic compounds dissociate in aqueous solution and molecular compounds do not, the total concentration of ions is lowest in CH₃OH (0.10 M). The other solutions (all ionic) have total solute concentrations greater than 0.10M. Volatile Correct Answer: Having a significant vapor pressure at a given temperature osmotic pressure equation 17 Correct Answer: π = iMRT Which of the following ions will contribute most to elevating the boiling point of H₂O? Correct Answer: All will contribute equally. Because boiling point elevation is a colligative property, it depends only on the concentration of solute, not the type of solute. All will contribute equally. Because boiling point elevation is a colligative property, it depends only on the concentration of solute, not the type of solute. Correct Answer: Vapor pressure describes the tendency of a substance to change from the liquid to the gas phase, so substances with weaker intermolecular forces will have higher vapor pressures. A substance's boiling point is also indicative of the strength of the intermolecular forces, with weaker intermolecular forces resulting in lower boiling points. Because acetone has the lowest boiling point of the options given, it has the weakest intermolecular forces, and will therefore have the highest vapor pressure. diffusion Correct Answer: Diffusion is the movement of a substance from an area of high concentration to an area of lower concentration. In this picture, the purple substance moves from a concentrated area to become dispersed throughout the aqueous solution. osmosis 18 Correct Answer: Osmosis is the movement of solvent molecules (often water) through a semipermeable membrane from a less concentrated solution into a more concentrated one resulting in similar concentrations on each side of the membrane. When an electrolyte solution (such as NaCl) is added to ice, the ions have ______ with water molecules and thus ______the ability of the water molecules to form a solid ice structure. Correct Answer: When an electrolyte solution (such as NaCl) is added to ice, the ions have strong intermolecular interactions with water molecules and, thus, decrease the ability of the water molecules to form a solid ice structure. A strong intermolecular attraction between the ions and water can prevent water molecules from packing tightly with each other. CaCl₂ is often used to melt ice on sidewalks. Calcium chloride is more effective at melting ice than NaCl. Choose the best explanation for this observation. Correct Answer: CaCl₂ dissociates into three ions increasing the concentration of solute species in solution. The ions have strong intermolecular interactions with water molecules and, thus, decrease the ability of the water molecules to pack tightly with each other. The more ions present, the harder it is to crystallize water into ice. _________ is a measure of the tendency of a material to change into the gaseous state 19 Correct Answer: Vapor pressure is a measure of the tendency of a material to change into the gaseous state. The molecules are moving rapidly and if they have enough energy they will escape from the liquid. The boiling point of a liquid is the temperature at which its vapor pressure is _______ the pressure of the gas above it. A liquid with strong intermolecular attractions will have a _______ vapor pressure and a higher boiling point Correct Answer: The boiling point of a liquid is the temperature at which its vapor pressure is equal to the pressure of the gas above it. A liquid with strong intermolecular attractions will have a low vapor pressure and a higher boiling point. What is the strongest intermolecular force in an aqueous sodium chloride solution? Correct Answer: The strongest intermolecular force in an aqueous sodium chloride solution is ion-dipole. The oxygen of water is partially negative and attracted to the positively charged sodium ions. The hydrogen atoms of water have a partially positive charge, which is attracted to the negatively charged chloride ions. The intermolecular force between the water and the ions in solution is stronger than the intermolecular force between two water molecules. The presence of the solute (NaCl) will cause the vapor pressure to ______ and will ______ the boiling point. Correct Answer: The intermolecular force between the water and the ions in solution is stronger than the intermolecular force between two water molecules. The presence of 20 the solute (NaCl) will cause the vapor pressure to decrease and will increase the boiling point of the solution. Given that water's freezing point is 0.00ºC and the freezing point depression constant (Kf) is 1.86 ºC･kg/mol, calculate the freezing point depression for a 3.00 molal solution (moles/kg) of NaCl in water. Assume ideal behavior of the ions. Correct Answer: The following solution may contain one or more values that are different from the problem provided to you, however, the steps to solve the problem are the same. ΔT = i × Kf × m i = number of dissociated ions Kf = 1.86° m = 3.00 molal solution The boiling point of a liquid is the temperature at which its vapor pressure is _______ the pressure of the gas above it. Correct Answer: The boiling point of a liquid is the temperature at which its vapor pressure is equal to the pressure of the gas above it. Which of the following substances would have the greatest dispersion forces? 21 Correct Answer: Dispersion forces arise from instantaneous changes in electron density, so compounds with more electrons tend to have greater dispersion forces. Since I₂ has the most electrons of the options given, it has the greatest dispersion forces. Which of the following would exhibit hydrogen bonding in a pure substance? Correct Answer: Hydrogen bonding results when a hydrogen atom is covalently bonded to the highly electronegative N, O, or F atoms, resulting in a large partial positive charge on the H atom. Since CH₃CH₂OH is the only option with H bonded directly to one of these atoms (O), it would exhibit hydrogen bonding. immiscible Correct Answer: liquids that are not soluble in each other (ex: oil and water) miscible Correct Answer: Describes two liquids that are soluble in each other Dispersion forces are due to Correct Answer: temporary dipoles Polarizability refers to Correct Answer: the ease with which the electron cloud of an atom or molecule can be distorted 22 For a molecule to exhibit dipole-dipole interactions, it must Correct Answer: have a permanent dipole moment Which combination of properties would be expected to lead to the most viscous liquid? Correct Answer: Viscosity is defined as a liquid's resistance to flowing, so compounds with stronger intermolecular forces will have higher viscosities. High temperature provides molecules with enough energy to overcome attractive forces, therefore, low temperatures lead to more viscous liquids. Molality equation Correct Answer: moles of solute/kg of solvent (mol/kg) Clausius-Clapeyron Equation Correct Answer: The equation below can be used with just two measurements of vapor pressure and temperature Raoul's Law Correct Answer: a law stating that the partial pressure of a solvent over a solution, Pa, is given by the vapor pressure of the pure solvent, POa, times the mole fraction of a solvent in the solution, Xa: Pa = XaPOa