Chem 1721 Review Exam 1

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1 Chem 1721 Review Exam 1 Given below are rough outlines of chapters 10 (partial) 12. These are the major concepts with which you should be wellacquainted. As this is just an outline, it is not meant to be a substitute for your notes or for the text. You are responsible for all material covered in lecture and in the textbook. Chapter 10: Molecular Geometry and Chemical Bonding Theory (partial) VSEPR Theory, Molecular Geometry, and Dipole Moments use to predict electron region and molecular geometries and bond angles use to predict preferred lone pair arrangement in trigonal bipyramidal and octahedral geometries effect of lone pairs or multiple bonds on bond angles in compounds use to predict compound polarity based on geometry (as opposed to bond polarity) Valence Bond Theory interpretation of covalent bond formation in terms of atomic orbital overlap hybridization mixing of a specific number of s, p, or d orbitals to form hybrid orbitals understand how many hybrid orbitals form from atomic orbital mixing, what they look like, the bond angles between the hybrid orbitals, and the molecular geometries that correspond to sp, sp 2, sp 3, sp 3 d, and sp 3 d 2 hybridization of the central atom σ vs π bonds understand the difference in regions of electron density concentration and orbital overlap (which orbitals overlap? and where do they overlap?), and the relationship between σ, π and multiple bonds you should be able to look at a molecule and give a complete description of its bonding including: identification of the hybridization of each atom, geometry around the central atom, bond angles between atoms, what orbital overlap is responsible for each bond, and an accounting of the total number of σ and π bonds in the molecule Chapter 11: States of Matter; Liquids and Solids Solids vs. Liquids vs. Gases characteristics of the 3 physical states relative arrangement and order of particles in each state kinetic energy of particles relative to intermolecular forces of attraction Intermolecular Forces 4 types of intermolecular forces: ion-dipole forces (mostly in solutions of ionic compound dissolved in polar solvent) and van der Waal s forces which include dipole-dipole forces, London dispersion forces and hydrogen bonding understand when the different forces are present and their relative strengths flow chart for determining which types of intermolecular forces are present in substances Liquids viscosity; how does viscosity change with strength of intermolecular forces and temperature? surface tension; how does surface tension relate to capillary action and cohesive and adhesive forces within a liquid? Phase Changes ΔH associated with physical state changes heating and cooling curves what happens when a substance is heated or cooled? ΔT or phase change (at mp or bp)? and associated calculations critical temperature and pressure superheating and supercooling Vapor Pressure pressure exerted by vapor of substance when liquid and vapor phases are in dynamic equilibrium understand relationship between vapor pressure, boiling point and volatility dependence of vapor pressure on temperature given by the Clausius-Clapeyron equation Phase Diagrams interpretation of phase diagram including correct identification of regions (s, l, or g), curves or lines separating regions, and critical and triple points

2 Solids crystalline vs. amorphous solids crystal structures defined by a crystal lattice and corresponding unit cell (see tables below) calculations based on unit cell of substance to determine percent occupied volume and density types of solids and their characteristic bonding and properties: ionic, molecular, covalent-network, and metallic crystal lattice unit cell # of spheres per unit cell % space occupied simple cubic primative cubic 1 52% body centered cubic (bcc) body centered cubic 2 68% cubic close-packed (ccp) ABC face centered cubic (fcc) 4 74% ABC layer pattern hexagonal close-packed (hcp) AB AB AB layer pattern hexagonal prismatic 6 74% sphere location in unit cell shared between how many cells? corner 8 face 2 edge 4 within cell 0 Chapter 12: Solutions Process of Solution Formation thermodynamic considerations of solution formation: process may be endothermic or exothermic but always proceeds with an increase in entropy (disorder) Factors that Affect Solubility nature of solute and solvent interactions like dissolves like nonpolar solutes tend to be more soluble in nonpolar solvent polar solutes tends to be more soluble in polar solvents temperature in general, the solubility of most solids will increase with increasing temperature the solubility of a gas will decrease with increasing temperature pressure the solubility of liquids and solids is not generally affected by changes in pressure the solubility of a gas will increase as pressure increases; relationship given by Henry's Law Expressions of Solution Composition you should know the definition of the following terms, and be able to do calculations to determine the various relationships: mass percent composition parts per million (ppm) parts per billion (ppb) mole fraction (χ) molality (or molal concentration, m) molarity (or molar concentration, M) Properties of Solutions vapor pressure the addition of a nonvolatile solute to a solvent will result in a solution with a lower vapor pressure than the vapor pressure of the pure solvent Raoult's Law: P soln = χ solv Pº solv if a solution is composed of 2 volatile components, each component will follow Raoult's Law freezing point depression the freezing point of a solution is lower than the freezing point of the pure solvent ΔT f = K f m

boiling point elevation the boiling point of a solution is higher than the boiling point of the pure solvent ΔT b = K b m osmotic pressure osmosis is the net movement of solvent molecules through a

3 boiling point elevation the boiling point of a solution is higher than the boiling point of the pure solvent ΔT b = K b m osmotic pressure osmosis is the net movement of solvent molecules through a semi-permeable membrane from a region of lower concentration to a region of higher concentration the osmotic pressure is the pressure required to to osmosis Π = MRT properties of solutions can be used to determine the molar masses of solutes you should understand the different behavior of electrolyte vs. nonelectrolyte solutes - particularily in terms of conentration and the effet on solution properties Some review problems: The purpose of these review problems is simply to provide you with extra practice. In no way should you interpret these problems to be a representation of the exam. In other words... DO NOT EXPECT THE EXAM TO LOOK LIKE THIS!! 1. Explain the bonding in the each of the following compounds. Identify the hybridization of the central atom, the bond angles, and the orbitals that overlap for bond formation. + a. AsH 3 b. BeF 3 c. BrF 3 d. AsCl 5 e. ClF 4 f. PF 5 g. C 2 H 4 2. Consider the following reaction: BF 3 + NH 3 F 3 B-NH 3. Describe any changes in hybridization (if any) of the B and N atoms as a result of this reaction. 3. What hybrid orbitals are used by nitrogen atoms in the following species? a. NH 3 b. H 2 N-NH 2 c. NO 3 4. The allene molecule H 2 C=C=CH 2 is linear with the 3 carbon atoms lie in a straight line. What is the hybridization of each carbon atom? Draw diagrams to show the formation of sigma and pi bonds in allene. 5. How many sigma and pi bonds are in each of the following molecules? 6. Identify the most important type of intermolecular force present in each of the following: a. BaSO 4 g. H 2 O b. H 2 S h. C 6 H 6 c. Xe i. CH 3 Cl d. C 2 H 6 j. PF 3 e. CsI k. CS 2 f. P 4 7. Predict which substance in each of the following pairs would have the greatest intermolecular forces: a. PF 3 or PF 5 b. SF 2 or SF 6 c. SO 3 or SO 2 8. Rationalize the difference in normal boiling points for each of the following pairs of substances: a. dimethyl ether, CH 3 OCH 3 bp = 25 C and ethanol, CH 3 CH 2 OH, bp = 79 C b. HF, bp = 20 C and HCl, bp = 85 C c. HCl, bp = 85 C and LiCl, bp = 1360 C d. n-pentane, CH 3 CH 2 CH 2 CH 2 CH 3 bp = 36.2 C and n-propane, CH 3 CH 2 CH 3 bp = 42 C e. n-propane, CH 3 CH 2 CH 3 bp = 42 C and dimethyl ether, CH 3 OCH 3 bp = 25 C

4 9. Cobalt has a cubic close packed structure and an atomic radius of 125 pm. Calculate the density (in g/cm 3 ) of Co. 10. Calculate the total energy required to convert kg of ice at 20 C to steam at 250 C. For water: molar mass = g/mol, ΔH fus = 6.02 kj/mol, ΔH vap = 40.7 kj/mol, mp = 0 C, bp = 100 C, s for H 2 O (s) = 2.1 J/g C, s for H 2 O (l) = 4.18 J/g C, s for H 2 O (g) = 2.0 J/g C. 11. Classify each of the following solids as ionic, molecular, metallic, or covalent-network. a. CO 2 f. I 2 b. SiO 2 g. KBr c. Si h. H 2 O d. CH 4 i. NaOH e. Ru j. PH Explain the term polarizeability. What kind of molecules tend to have high polarizeabilities? What is the relationship between polarizeability and intermolecular forces? 13. The compounds Br 2 and ICl have the same number of e s, but Br 2 melts at 7.2 C and ICl melts at 27.2 C. Explain. 14. If you lived in Alaska, which of the following natural gases would you keep in an outdoor storage tank in winter? methane (CH 4 ), propane (C 3 H 8 ), or butane (C 4 H 10 )? Explain why. 15. Which of the following species are capable of intermolecular hydrogen bonding? C 2 H 6, HI, KF, BeH 2, or CH 3 COOH 16. Arrange the following in order of increasing boiling point: RbF, CO 2, CH 3 OH, CH 3 Br 17. a. Which of the following will have the higher boiling point? O 2 or Cl 2 b. Which of the following will have the lower melting point? HF or HI c. Which of the following will have the highest vapor pressure? CH 4 or Cl 2 d. Which of the following will have the lower boiling point? Ne or Xe 18. What is viscosity? What is the relationship between viscosity and intermolecular forces? What is the relationship between viscosity and temperature? 19. Predict which of the following liquids has greater surface tension: ethanol (CH 3 CH 2 OH) or dimethyl ether (CH 3 OCH 3 ). 20. Crystalline silicon has a cubic structure. The unit cell edge length is 543 pm. The density of the solid is 2.33 g/cm 3. Calculate the number of Si atoms in one unit cell. 21. a. A solid is hard, brittle, and electrically nonconducting. Its melt (liquid form of the substance) and aqueous solution containing the substance conduct electricity. Classify the solid. b. A solid is soft and has a low melting point (below 100 C). The solid, its melt, and an aqueous solution containing the substance are all nonconductors of electricity. Classify the solid. c. A solid is very hard and has a high melting point. Neither the solid or its melt conduct electricity. Classify the solid. 22. Use any one of the phase changes to explain what is meant by the term dynamic equilibrium. 23. a. What can you learn about the strength of intermolecular forces of attraction in a substance by it molar enthalpy of vaporization? b. True or False: The greater the molar heat of vaporization of a liquid the greater its vapor pressure. 24. The molar heats of fusion and sublimation of molecular iodine are kj/mol and kj/mol respectively. Estimate the molar heat of vaporization of liquid iodine. 25. The vapor pressure or benzene is 40.1 mmhg at 7.6 C. What is the vapor pressure of benzene at 60.6 C? For benzene, C 6 H 6, ΔH vap = 31.0 kj/mol. 26. Estimate ΔH vap of a liquid whose vapor pressure doubles when the temperature is raised from 85 C to 95 C.

5 27. The normal boiling point and normal freezing point of sulfur dioxide are 10 C and 72.7 C respectively. The triple point is 75.5 C and 1.65 x 10 3 atm, and its critical point is 157 C and 78 atm. Use this information to sketch the phase diagram of SO Which of the following properties indicates very strong intermolecular forces? a. low surface tension b. low critical temperature c. low boiling point d. low vapor pressure 29. What is the vapor pressure of mercury at its normal boiling point (357 C)? 30. Which has a greater density - crystalline SiO 2 or amorphous SiO 2? Explain. 31. Br 2 is much more soluble in CCl 4 than in water. Explain why. 32. Why do ionic compounds wtih higher lattice energies tend to be less soluble in water than substances with lower lattice energies? 33. Ethanol (CH 3 CH 2 OH) is miscible with water at 20ºC, but pentanol (CH 3 CH 2 CH 2 CH 2 CH 2 OH) is soluble in water only to the extent of 2.7 g per 100 ml. Explain. 34. Propranolol (C 16 H 21 NO 2 ), a beta-blocker that is used for the treatment of high blood pressure, is effective at a blood plasma concentration of 50 ng/l. Express this concentration in the following units: a. parts per billion (assume a plasma density of g/ml) b. molarity 35. Residues of the herbicide atrazine (C 8 H 14 ClN 5 ) in water can be detected at concentrations as low as µg/l. Express this concentration in the following units: a. parts per million (assume a solution density of g/ml) b. molarity 36. a. Determine the mass (in g) of glucose (C 6 H 12 O 6 ) required to prepare ml of a M solution. b. Determine the mass (in g) of CaBr 2 required to prepare ml of a solution with [Br ] = M. c. Determine the mass (in g) of benzoic acid (C 7 H 6 O 2 ) required in combination with 775 g chloroform (CHCl 3 ) to prepare a m solution. 37. Determine the mass percent of solute in each of the following solutions: a mol citric acid (C 6 H 8 O 7 ) dissolved in 1.00 kg water. b. 135 mg KBr dissolved in 5.00 ml of water (d = 1.00 g/ml). c g aspirin (C 9 H 8 O 4 ) dissolved in 145 g dichloromethane (CH 2 Cl 2 ). 38. Determine the molal concentration of each solution described in question 37 above. 39 a. What is the molality of a solution prepared by dissolving 25.0 g H 2 SO 4 in 1.30 L water (d = 1.00 g/ml)? b. What is the mole fraction of each component in a solution prepared by dissolving 2.25 g nicotine (C 10 H 14 N 2 ) in 80.0 g CH 2 Cl 2? 40. The density of a 16.0 mass % solution of sulfuric acid in water is g/ml. Determine the molar concentration of this solution. 41. Ethylene glycol(c 2 H 6 O 2 ) is the principal constituent of automobile anti-freeze. If the density of a 40.0 mass % solution of ethylene glycol in water is g/ml, determine the molarity of the solution. 42. Vinyl chloride (H 2 CCHCl) is the starting material from which PVC polymer is made. The Henry's law constant for vinyl chloride is mol/l atm at 25ºC. Determine the concentration of dissolved vinyl chloride in water at 25ºC and partial pressure of 0.75 atm.

6 43. What is the vapor pressure in torr of the following solutions? For water at 45ºC, vapor pressure = torr. a. a solution of 10.0 g urea (CH 4 N 2 O - a nonvolatile, nonelectrolyte solute) in g water at 45ºC b. a solution of 10.0 g LiCl (a nonvolatile solute) in g water at 45ºC; assume that LiCl is completely dissociated 44. Determine the vapor pressure (in torr) of a solution prepared by dissolving 16.0 g glucose (C 6 H 12 O 6 - a nonvolatile, nonelectrolyte solute) in 80.0 g methanol (CH 3 OH) at 27ºC. The vapor pressure of pure methanol at this temperature is 140 torr. 45. Acetone (C 3 H 6 O) and ethyl acetate (C 4 H 8 O 2 ) are volatile organic liquids frequently used as solvents. At 30ºC the vapor pressure of acetone is 285 torr, and the vapor pressure of ethyl acetate is 118 torr. Determine the vapor pressure of a solution (in torr) composed of 25.0 g acetone and 25.0 g ethyl acetate. 46. A solution is prepared by dissolving 5.00 g aspirin (C 9 H 8 O 4 ) in 215 g chloroform (CHCl 3 ). The boiling point of the solution is elevated by 0.47ºC over the bp of pure chloroform. Determine the value of K b for CHCl A solution of an unknown molecular substance in water at 300 K has an osmotic pressure of 4.85 atm. Determine the molar concentration of the solution. 48. Cellobiose is a sugar obtained by the degradation of cellulose. If ml of an aqueous solution containing g of cellobiose at 25ºC has an osmotic pressure of torr, what is the molar mass of cellobiose? 49. Elemental analysis of beta-carotene, a dietary soruce of vitamin A, shows that it is composed of 10.51% H and 89.49% C by mass. Dissolving g of β-carotene in 1.50 g of camphor gives a freezing point depression of 1.17ºC. Determine the molar mass and molecular formula of β-carotene. For camphor, K f = 37.7ºC/m. 50. Determine the mass (in g) of ethylene glycol (C 2 H 6 O 2 ) that must be dissolved in 3.55 kg of water to lower the freezing point of water in an automobile radiator to 22.0 ºC. For water, K f = 1.86ºC/m.

7 Chem 1721: Review Exam 1 Answers 1. a. sp 3 ; σ bonds As sp 3 /H 1s; <109.5 b. sp 2 ; σ bonds Be sp 2 /F sp 3 ; 120 c. sp 3 d; σ bonds Br sp 3 d/f sp 3 ; 90 and 120 d. sp 3 d; σ bonds; As sp 3 d/cl sp 3 ; 90 and 120 e. sp 3 d; σ bonds; Cl sp 3 d/f sp 3 ; 90 and 120 f. sp 3 d; σ bonds; P sp 3 d/f sp 3 ; 90 and 120 g. sp 2 ; σ bonds C sp 2 /C sp 2 and C sp 2 /H 1s, and 1 π bond C p/c p; B sp 2 sp 3 ; N sp 3 throughout 3. a. sp 3 b. sp 3 c. sp σ bonds, 3 π bonds; 9 σ bonds, 9 π bonds; 13 σ bonds, 3 π bonds 6. a. ionic f. London dispersion forces b. dipole-dipole g. hydrogen bonding c. London dispersion forces h. London dispersion forces d. London dispersion forces i. dipole-dipole forces e. ionic j. dipole-dipole forces k. London dispersion forces 7. a. PF 3 because it is polar b. SF 2 because it is polar c. SO 2 because it is polar 8. a. CH 3 CH 2 OH can hydrogen bond; CH 3 OCH 3 has only dipole-dipole forces b. HF can hydrogen bond; HCl has only dipole-dipole forces c. LiCl is ionic d. both are non-polar; n-pentane is larger and will have stronger London dispersion forces e. CH 3 OCH 3 has dipole-dipole forces; n-propane has only London dispersion forces 9. d = 8.85 g/cm q tot = 1700 kj (2 sig figs) 11. a. molecular f. molecular b. covalent-network g. ionic c. metallic or covalent-network h. molecular d. molecular i. ionic e. metallic j. molecular

8 12. polarizeability ability of an atom s electron cloud to be distorted; generally larger (higher molar mass) species have greater polarizeability; the more polarizeable the substance the stronger the London dispersion forces 13. Br 2 is non-polar, London dispersion forces only; ICl is polar, dipole-dipole forces + LDF 14. CH 4 because it is smaller and will have the weakest London dispersion forces and therefore the lowest freezing point (will be liquid to a lower T) 15. CH 3 COOH 16. CO 2 < CH 3 Br < CH 3 OH < RbF 17. a. Cl 2 ; both non-polar but Cl 2 has stronger LDF b. HI; both polar but HF can hydrogen bond c. CH 4 ; both non-polar but CH 4 has weaker LDF and lower bp d. Ne; both non-polar but Ne has weaker LDF 18. viscosity resistance to flow; viscosity increases as strength of intermolecular forces increases; viscosity decreases as temperature increases 19. CH 3 CH 2 OH because it can hydrogen bond and therefore has stronger intermolecular forces Si atoms per unit cell 21. a. ionic b. molecular c. covalent-network 22. dynamic equilibrium process occurs in both forward and reverse direction at equal rate; the net population (number of particles) in each phase remains constant once equilibrium is reached 23. a. higher ΔH vap means that more energy is required to cause l g change, i.e. stronger intermolecular forces of attraction b. False higher ΔH vap suggests fewer particles in gas phase (because the energy cost to get there is high), and therefore lower vapor pressure kj/mol mmhg (331 Torr) kj/mol 27.

9 28. d lower vapor pressure correlates to low volatility and higher bp, i.e. stronger intermolecular forces Torr or 1 atm 30. crystalline SiO 2 atoms in more ordered structure therefore the structure is more condensed and the solid has higher density 31. Br 2 is nonpolar and so it is more soluble in nonpolar CCl 4 than in polar H 2 O. 32. Lattice energy is a measure of the strength of the force holding ions together as an aggregate unit in the solid state. The higher the lattice energy, the harder it will be to separate or dissociate the ions, therefore water solubility will be lower. 33. Ethanol is more polar and will be miscible with water. Pentanol has a much bigger nonpolar hydrocarbon component and is therefore less polar and has lower solubility in water. 34. a ppb b. 1.9 x M 35. a. 5.0 x 10 5 ppm b. 2.3 x M 36. a g glucose b g CaBr 2 c g benzoic acid 37. a. 11.9% citric acid by mass b. 2.63% KBr by mass c. 3.65% aspirin by mass 38. a m b m c m 39. a m b. χ C10H14N2 = χ CH2Cl2 = M M mol/l 43. a torr b torr torr torr 46. K b = 3.6 ºC/m M g/mol g/mol; C 40 H x 10 3 g C 2 H 6 O 2

PX-III Chem 1411 Chaps 11 & 12 Ebbing

PX-III Chem 1411 Chaps 11 & 12 Ebbing 1. What is the name for the following phase change? I 2 (s) I 2 (g) A) melting B) condensation C) sublimation D) freezing E) vaporization 2. Which of the following