| Name _______________________________________ | Gen Chem II Lecture |
| Exam 3 | 27MAR98 | 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. |
Nitrobenzene [C6H5NO2 ; MW = 123.16]is a good solvent for many organic compounds. Nitrobenzene has a normal boiling point of 210.88 °C with a kb of 5.24 and a normal freezing point of 5.70 °C and a kf of 7.00. Reserpine is a natural product that has been used as a tranquilizer. The freezing point of a solution containing 3.00 g of resperine (a nonelectrolytic, nonvolatile solute) in 25.0 g of nitrobenzene is 4.32 °C. Calculate the molecular weight of resperine. [10] |
| 2. | 0.0404 grams of O2 will dissolve in 1.00 L of water at 25 °C when the partial pressure of oxygen is 1.00 atm. What is the solubility of oxygen gas in water, at 25 °C, when the partial pressure of oxygen is 159 mm Hg? [8] |
| 3. | Please explain why oil and water are not miscible. [5] |
| 3. | Please explain why oil and water are not miscible. [5] |
| 4. | A mass of sucrose [C12H22O11], was completely dissolved in a mass of H2O and solution resulted. The resulting solution has a density of 1.10 g/mL and a molality of 0.638. The vapor pressure of water at 20.0°C is 17.54 torr. Calculate the following concentration units. [please define each concentration unit.] |
| [a] the wt-wt % C12H22O11 | |
| [15] | [b] the mole fraction of C12H22O11 |
| [c] the molarity of the solution ... M |
| 5. | Consider the following equations: |
| [1] MX2(s) Æ M2+(g) + 2 X-(g) E1 = 345 kJ | |
| [10] | [2] M2+(g) + 2 X-(g) + xs H2O (l) Æ M2+(aq) + 2 X-(aq) E2 = -625 kJ |
| Using this data explain how and why the solubility of MX2(s) will be effected by an increase in temperature. The solubility will INCREASE or DECREASE [circle one] because ___________ |
| 6. | 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] | Le Chatelier's Principle | |
| [2] | interstitial solid solution | |
| [3] | supersaturated solution | |
| [4] | molecularity | |
| [5] | ideal solution | |
| [6] | heterolytic bond cleavage | |
| 7. | FeCl3 dissolves in water
according to the following equation: FeCl3(aq) + H2O(l) Æ Fe3+(aq) + 3 Cl-(aq) A solution is prepared by dissolving 1.89 g of FeCl3 in enough water to yield 250.0 mL of solution. The osmotic pressure of this solution was determined to be 4.22 atm at 27.0°C. Calculate i and the apparent percentage ionization of the FeCl3 solution.[13] |
| 8. | Write the rate expression for the following reaction: 4 Cl2(g) + 4 H2O(g) Æ 8 HCl(g) +2 O2(g) [3] _______________________________________________________________________________ |
| 9. | What are the four factors that influence the rate of a chemical reaction? [4] |
| ___________________________________ and _______________________________________ | |
| ___________________________________ and _______________________________________ |
| 10. | A certain reaction is first order in reactant A and third order in reactant B. If the concentrations of both reactants are doubled, what happens to the reaction rate? [3] |
| 11. | If you are given a four step mechanism with which to explain an overall reaction, what information must you be given in order to write the rate expression for the reaction? [3] |
| 12. | The observed rate law expression for the reaction
. . . 2 NO2(g) + Cl2(g) Æ 2 NO2Cl(g) is . . . Rate = k[NO2]Cl2] Please state what this rate expression indicates about the reaction . . . . [4] |
| 13. | For the following reaction: x A(g) +y B(g) + z C(g) Æ Products, the data presented was obtained in the laboratory. On the basis of this data determine the |
| [a] order with respect to A ______________ [c] order with respect to C ______________ | |
| [b] order with respect to B ______________ [d] value of rate constant ______________ |
|
EXP. NO. |
[A] |
[B] |
[C] |
RATE |
|
|
1 |
0.0125 |
0.0456 |
0.0253 |
0.3618 |
|
|
2 |
0.0250 |
0.0456 |
0.0253 |
1.4474 |
|
|
3 |
0.0250 |
0.0456 |
0.0886 |
62.1610 |
|
|
4 |
0.0375 |
0.0872 |
0.0886 |
139.8600 |
| Extra Credit . . . if you like |
|
The vapor pressure of benzene [C6H6; M.W. =78.11 g/mol] is 94.4
torr at 25 °C. 156.2 grams of benzene is mixed with 122.6 grams of the unknown volatile nonelectrolytic solute. The vapor pressure of the resulting solution is 207.4 torr at 25 °C. Calculate the molecular weight of the unknown solute. [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 = 106 points |