CHM101, Section 5, Fall 2000
Final exam, Thursday 21 December 2000
Chapters 1–12

Instructions:
      Read over the entire exam first. Begin with the questions you feel most confident about. Pace yourself so that you will have time enough to try everything. If you don’t know how to get all the way to an answer, go as far as you can and state how you would approach the rest. And keep your handwriting neat! Use the back of the sheets if necessary.

Definitions (2 points each; 20 points total)

      1. Polar molecule
      2. Sigma (s) bond
      3. Hydrogen bonding
      4. Sublimation
      5. Molality
      6. Formal charge
      7. Bond order
      8. Transition metal
      9. Principal shell
      10. Charles’s law

Short answers (4 points each; 40 points total)

      1. Use orbital diagrams (the sets of little boxes) and the concept of hybridization to explain why carbon can bond to more than two other atoms at once.
      2. A beaker of water is placed into a bell jar that contains dry air. Explain what happens at the surface of the water as the vapor pressure of water in the air approaches and eventually reaches equilibrium.
      3. Draw the Lewis structure for ammonia (NH₃) and use the result to describe its molecular shape.
      4. Draw the Lewis structure for water. What is its molecular shape? Why is the H–O–H angle a few degrees smaller than predicted?
      5. Why are there such things as water droplets in the atmosphere? Why don’t the molecules simply disperse?
      6. When beginning to draw the Lewis structure of the molecule CH₃NH₂, how do we know which atom to place at the center of its structure?
      7. Name each of these elements: V ______________________ Ti_____________________ Be ______________ Br _____________
      8. Round of these numbers as directed:

            (a) 123 to 2 sig. figs. ___________ (b) 0.018 to 1 sig. fig. _________ (c) 535 to 2 sig. figs ___________ (d) 9.218x10⁴ to 3 sig. figs. _________

      9. Use the periodic table to predict the most common oxidation number for the elements listed below. Give the reason for each answer.

      (a) Be ________ (b) Sc _________ (c) Se _________ (d) I ________

      10. Give the electronic configurations for each of these elements:

            (a) Y ________________________________________
            (b) As _______________________________________

Longer answers (10 points each; 40 points total)

      1. Draw the phase diagram of a typical substance and show the zones where gas, liquid, solid, and supercritical fluid are found.
      2. Show in detail (with a drawing) why groups of atoms cannot rotate about double or triple bonds.
      3. Explain why hydrogen bonding in water makes possible life on earth as we know it.
      4. Draw the temperature-density diagram for water and ice below about 10 ºC and use it to show why (a) ice floats; (b) the coldest water of a pond is found at the top during winter; and (c) there are pairs of temperatures of water with the same density.

Problems (10 points each; 100 points total)

Planck’s constant h = 6.626x10^-34 J s         c = 3.00x10⁸ m s^-1
R = 0.082058 L atm K^-1 mol^-1                 1 atm = 101.325 kPa = 760 Torr = 760 mmHg

      1. Show the orbitals that make up the single and double bonds in ethylene, C₂H₄.
      2. Draw the 3-D Lewis structure for BF₃ and describe its shape.
      3. Draw the 3-D Lewis structure for PCl₅ and describe its atomic shape. How can more than four atoms be bonded to the P?
      4. Draw the Lewis structure or resonance structures for SO₂ and describe its atomic shape.
      5. Sodium tetrathionate is 17.01% Na, 47.46% S, and 35.52% O by mass. Its formula mass is 270 u. What is its molecular formula?
      6. Toluene and nitric acid are used to produce trinitrotoluene, the infamous explosive TNT:

C₇H₈ + HNO₃ → C₇H₅N₃O₆ + H₂O
(not balanced)

      How many grams of TNT can be made when 829 g of toluene reacts with excess nitric acid?
      7. Balance this redox equation and show your work:

BiO₃^- + Mn²⁺ + H⁺ → Bi³⁺ + MnO₄^- + H₂O

      8. The atmosphere at the surface of Mars has an average temperature of –48 ºC and an average pressure of 8 mmHg. What is the molar volume of gases there?
      9. Explain how and why atomic radii vary from left to right across a row and down a column of the periodic table.
      10. A NMR (Nuclear Magnetic Resonance) spectrometer uses electromagnetic radiation at a frequency of 200 MHz. What wavelength, in meters, does this correspond to?

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