Chem Midterm 3 April 23, 2009

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Arlene Quinn
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1 Chem Midterm 3 April 3, 009 Name All work must be shown on the exam for partial credit. Points will be taken off for incorrect or no units and for the incorrect number of significant figures. Only a non graphing calculator is allowed. On short problems you must show your work in order to receive credit for the problem. If your cell phone goes off during the exam you will have your exam removed from you. Page (of 1 possible) Page 3 (of 14 possible) Page 4 (of 11 possible) Page 5 (of 1 possible) Page 6 (of 1 possible) Multiple Choice (of 30 possible) Subtotal 1

2 1a) pts What is the Lewis Symbol for Sn? 1b) pts What is the Lewis Symbol for Ga? 1c) pts What is the Lewis Symbol for Ar? a) 3 pts What is the Ionic Lewis structure for NaCl? b) 3 pts What is the Ionic Lewis structure for SrBr? 3a) 3 pts What is the covalent Lewis structure for N H 4? 3b) 3 pts What is the covalent Lewis structure for C H 6? 3c) 3 pts What is the covalent Lewis structure for NCl 3?

3 4a) 3 pts What is the electronic shape, molecular shape, and bond angle of H S? Electron shape: tetrahedral Molecular shape: bent Angle: a) 3 pts What is the electronic shape, molecular shape, and bond angles of NH 3? Electron shape: tetrahedral Molecular shape: Trigonal pyramidal Angle: a) 4 pts Is C 3 O polar or nonpolar? You must show work to get credit. non polar 5a) 4 pts Is CH 3 F polar or nonpolar? You must show work to get credit. polar 3

4 6a) pts Temperature is a measure of the average_ of the molecules in a sample of gas. speed 6b) pts When the volume of a gas is decreased, the pressure of the sample of gas. (at constant temperature) increases 7) 4 pts If a 45.0 ml sample of gas at 6.5 C is heated to 55. C, what is the new volume of the gas sample (at constant pressure)? T1 6.5 C K V1 45.0mL T1 55. C K V? V1 V T1 T 45.0mL V 99.7K 38.4K V 49.3mL units 8) 3 pts A sample of oxygen gas is saturated with water vapor at 7 C. The total pressure of the mixture is 77 torr, and the vapor pressure of water is 6.7 torr at 7 C. What is the partial pressure of oxygen? P P + P P P 77torr P P tot tot H O O O 77torr 6.7torr O 745torr H O + 6.7torr units 4

5 9) 5 pts A sample of gas has a mass of g. Its volume is 4 ml at a temperature 55 C and a pressure of 886 torr. Find the molar mass of the gas. PV nrt PV n RT m mrt M n PV T 55 C K 1L V 4mL 0.4L 1000mL 1atm P 886torr 1.17atm 760torr m g M mpv RT Latm molk ( g) ( 38K ) 3.98 ( 1.17atm)( 0.4L) mol g units 10) 3 pts How much heat is required to melt 37.4 g of ice at 0 C? H fus 6.0 KJ/mol H O(s) + heat H O(l) H fus 6.0 KJ/mol 1molH O 6.0KJ 37.4gH O 1. 5KJ 18.0gH O 1molH O units 11) pts What intermolecular forces are present in H S? Dispersion, and dipole-dipole 1) pts What intermolecular forces are present in CO? Dispersion 5

6 13) pts Which has larger intermolecular forces solids, liquid, or gases? Solids 14) 3 pts A soft drink contains 45 g of sugar in 309 g of H O. What is the concentration of sugar in the soft drink in mass percent? 45g mass % 100% 13% 45g + 309g units 15) 4 pts If 4.5 g of CaBr is dissolved in enough water to make15 ml of solution, what is the molarity of the solution? 1molCaBr.5gCaBr.014molCaBr 199gCaBr n 0.014mol M.171M V 0.15L 4 units 16) 3 pts Calculate the volume of M HCl that we should use to prepare 100. ml of M HCl. V M V 1 1 V M 1L 100. ml.100l 100mL VM V1 M 1 4 ( 0.100L)( M ).00337L M units 6

7 Multiple Choice Questions CIRCLE THE CORRECT ANSWER 1) 3 pts Which term matches the definition: The ability of an element to attract electrons within a covalent bond. A) coulombic attraction B) dipole moment C) polar covalent D) nonpolar covalent E) electronegativity Answer: E ) 3 pts Which set of conditions reflect STP? A) 98 K, 1 atm B) 5 C, 14.7 psi C) 373 K, 760 torr D) 73 K, 1 Pa E) 73 K, 760 mm Hg Answer: E 3) 3 pts Suppose you had a balloon containing 1 mole of helium at STP and a balloon containing 1 mole of oxygen at STP. Which statement is true? A) The balloons will have the same volume. B) The balloons will have the same mass. C) Both A) and B) are true. D) Neither A) nor B) are true. E) not enough information Answer: A 4) 3 pts Increasing the intermolecular forces of a liquid will do which of the following? A) increase the viscosity B) decrease the evaporation rate C) increase the surface tension D) decrease the vapor pressure E) all of the above Answer: E 7

8 5) 3 pts Rank the compounds NH3, CH4, and PH3 in order of increasing boiling point. A) NH3 < CH4< PH3 B) CH4< NH3 < PH3 C) NH3 < PH3< CH4 D) CH4 < PH3 < NH3 E) PH3< NH3 < CH4 Answer: D 6) 3 pts Which intermolecular force found in CCl H is the strongest? A) dispersion force B) dipole-dipole force C) hydrogen bonding D) X-force E) none of the above Answer: B 7) 3 pts Dry ice (solid CO ) is which type of solid? A) molecular solid B) ionic solid C) covalent atomic solid D) nonbonding atomic solid E) metallic atomic solid Answer: A 8) 3 pts Which of the following substances is not a solution? A) homogenized milk B) bronze C) sea water D) soda E) All of the above are solutions. Answer: E 9) 3 pts Which of these compounds would you expect to be least soluble in water? A) CH3OH B) NaCl C) N D) NH3 E) not enough information Answer: C 8

9 10) 3 pts The solubility of gases in water: A) is independent of temperature. B) increases with increasing temperature. C) decreases with increasing temperature. D) gases are not soluble in water. E) none of the above Answer: C 9

States of Matter. The Solid State. Particles are tightly packed, very close together (strong cohesive forces) Low kinetic energy (energy of motion)

States of Matter. The Solid State. Particles are tightly packed, very close together (strong cohesive forces) Low kinetic energy (energy of motion) States of Matter The Solid State Particles are tightly packed, very close together (strong cohesive forces) Low kinetic energy (energy of motion) Fixed shape and volume Crystalline or amorphous structure