| Name _______________________________________ | Gen Chem II Lecture |
| Exam 2 | 27FEB98 | Dr. L. J. Rivela |
| 1. YOU MUST
SHOW ALL EQUATIONS, LOGIC, AND CALCULATIONS IN ORDER TO RECEIVE
ANY CREDIT ! 2. ALL NUMERICAL ANSWERS MUST HAVE THE PROPER NUMBER OF SIGNIFICANT FIGURES AND BE EXPRESSED IN SCIENTIFIC NOTATION WHERE NECESSARY. |
| 1. | A sample of gas occupies 3425 mL at 22.5 psi and 37.2 °C. Please calculate the pressure [in atmospheres] of 1.500 L of this gas at 37.2 °C. [10] |
| 2. | Calculate the temperature of methane gas, CH4, which has a density of 1.83 g/L at 725 torr. [10] |
| 3. |
A mixture of gases consists of 6.0 g of H2,
12.0 g of He, and 24.0 g of N2.
At 25 °C in a particular container the mixture exerts a pressure
of 1488 torr. [18] [b] Calculate the volume of the container. |
| 4. | Propane gas, C3H8, will react with oxygen gas to form carbon dioxide gas and water vapor. What volume of propane at 255 °C and 748 torr would combine with 125 liters of oxygen at 255 °C and 748 torr? [10] |
| 5. | An ice cube weighing 275.0 g, at a temperature of -37.0°C, was added to an unknown mass of liquid water at 75.0°C. The ice cube completely melted and the resulting liquid was found to have a temperature of 22.0°C. Calculate the mass of the original liquid water.[12] |
| 6. | Heavy water [deuterium oxide; D2O; MW = 20.03g/mol] is an isotopic modification of common water; H2O . At the normal boiling point (101.41°C), the heat of vaporization of heavy water is 41.606 kJ/mol. Calculate the vapor pressure of heavy water at 80.00°C. [10] |
| 7. | A 140. mL sample of heptane gas, contained in a vessel at 50.0°C, has a pressure of 75.0 torr. Calculate the pressure inside the vessel, if its volume is changed to 65.0 mL at 50.0°C. The vapor pressure of heptane at 50.0°C is 143 torr. [10] |
| 8. | Hydrogen cyanide, HCN, is a lethal vapor which can be released when an ionic cyanide comes in contact with acid solution. |
| [a] Draw the Lewis electron dot structure for the hydrogen cyanide molecule. | |
| [20] |
[b] What type of hybridization does carbon use in this compound ? [c] What type of hybridization does nitrogen use in this compound ? |
| [d] Show how carbon's and nitrogen's atomic orbitals hybridize in di-imide [i.e. . . . g.s. · e.s.· h.s.] | |
| [e] Draw appropriate diagrams to show how the hybrid and atomic orbitals overlap, in hydrogen cyanide , to form its bonds. Please label your diagrams clearly and completely. |
| 9. |
Indicate the type(s) of intermolecular forces that the following substances possess. [12] CF4 , CH3OH , CH2Cl2 |
| 10. | Please define 4 [four] of the following terms in SHORT, CONCISE STATEMENTS. [12] |
| Draw a line through the term not defined and please write clearly. If you do not delete those questions that you choose not to answer, then the first four questions will be graded ! |
| [1] | liquid crystal | |
| [2] | condensation polymerization reaction | |
| [3] | superconductivity | |
| [4] | ceramics | |
| [5] | piezoelectric | |
| [6] | amorphous solid | |
| 11. | A sample of unknown gas flows through the wall of a porous cup in 39.9 min. An equal volume of hydrogen, measured under the same temperature and pressure, flows through in 9.75 min. What is the molecular weight of the unknown gas? [10] |
| 12. | Please draw a clearly labeled PHASE diagram for water. [12] |
| Extra Credit . . . if you like |
| A fellow student comes to you with this problem: " I looked up the vapor pressure of water in a table; it is 26.7 torr at 300. K and 92,826 torr at 600. K. That means that when the absolute temperature doubles, the vapor pressure is multiplied by 3477. But I thought the pressure was proportional to the absolute temperature, P = nRT/V. Why doesn't the pressure just double? " How would you help the student? [10] |
| DATA: | R = 0.08206 L atm / mol K | NA = 6.0220453 x 1023 particles/mol | |
| 1 atm = 760 mm Hg | 1 atm = 14.7 psi | ||
| 1 atm = 101.325 kPa | 1 liter = 1000 mL | ||
| vp of H2O @ 24°C = 22.38 mm Hg |
| Total points = 158 points |