Professor Bunsen Honeydew

 

 

Chemistry 141 Problem Session 2

 

  1. Calculate the values of pH, pOH, [H3O+] and [OH-] for a solution that is 2.863 x 10-5 M in sulfuric acid.

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  2. 372 mL of 0.8265 M hydrochloric acid are mixed with 722 mL of 0.2019 M barium hydroxide. Calculate the pH of the resulting solution.

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  3. A primary acid standard is prepared by dissolving 1.2977 grams of oxalic acid dihydrate to a total volume of 500.0 mL. 25.00 mL of this solution reacts completely with 42.66 mL of a sodium hydroxide solution. If 3.8772 grams of an unknown diprotic acid are neutralized by 31.85 mL of the NaOH solution, what is the molecular mass of the unknown acid?

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  4. Define the following terms:
    1. octet rule
    2. antibonding molecular orbital
    3. delocalization
    4. bond angle
    5. bonding electron pair
    6. bond length
    7. bond order
    8. covalent bond
    9. electronegativity
    10. formal charge
    11. hybrid atomic
    12. Lewis structure
    13. lone pair electrons
    14. molecular orbital theory
    15. pi bond
    16. polar covalent bond
    17. resonance hybrid
    18. sigma bond
    19. Coordinate covalent bond
    20. electron affinity
    21. valence bond theory

     

  5. A photon with a wavelength of 415 nm strikes a metal surface ejecting an electron with a velocity of 9.0 x 105 m/sec. What is the threshold frequency of the metal? (kinetic energy = 1/2mv2, J = kg· m2/sec2)

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  6. Draw the orbitals associated with the following quantum numbers.

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    1. n = 4, l = 0, m = 0

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    2. n = 2, l = 1, m = 0

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    3. n = 3, l = 2, m = -2

     

     

     

     

     

  7. Consider the following levels of a hypothetical atom:

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    E8 0 J

     

    E4 - 1.0 x 10- 19

     

    E3 - 5.0 x 10- 19

     

    E2 - 10 x 10- 19

     

    E1 - 15 x 10- 19

     

    1. An electron in the E1 energy level will jump to a higher energy level when excited by light with a wavelength of 190 nm. Calculate the energy of the light beam.

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    2. Predict the energy level to which the electron will jump upon excitation by 190 nm light.

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    3. How many different emission lines would you predict as electrons fall from the E4 state back to the ground state by all possible routes. (Draw the possible transitions on the diagram using arrows.)

     

     

     

     

     

     

  8. Write the complete and shorthand electronic configuration for the following atoms and ions.

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    1. Si

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    2. Mg+2

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    3. S-2

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    4. V

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    5. Mn

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    6. Ni+2

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    7. W

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    8. Am

     

     

  9. Arrange the following from left to right in order of increasing size:

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    1. As, Br, Ga, Kr

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    2. Mg, Ba, Sr, Be

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    3. F- , Ne, F, O2-

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    4. K, K+, Ca+2, Sc+3

     

  10. The first ionization energy of gallium is greater than that of aluminum and the first ionization energy of thallium is greater than that of indium. Suggest a possible explanation based on effective nuclear charge.

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  11. Given the following ionization energy data:

    1. Explain why there is an increase in ionization energy from Al to Ar.

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    2. Explain the slight decrease in ionization energy from P to S.

     

     

     

     

     

     

     

  12. For each of the following pairs of ionic compounds circle the compound that has the higher lattice energy. Explain your choice in each case. (Remember that Elattice = k Q+Q- /d where k is a constant, Q’s are the ion charges and d is the distance between ions.)

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    1. LiF or LiBr

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    2. Mg3N2 or NaCl

     

     
  13. Tabun is a chemical warfare agent
    1. How many pi bonds are there in tabun?

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    2. How many sigma bonds are there in tabun?

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    3. Give the hybridization of each carbon, nitrogen and oxygen in the molecule.

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    4. Which is the shortest C- N bond in the molecule?

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    5. What is the P- C- N bond angle?

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    6. What is the C- N- C bond angle?

     

     

     

  14. Complete the following table

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    Molecule

    Lewis Diagram

    Orbital

    geometry

    molecular

    geometry

    Hybridization

    BrF5

     

     

     

     

     

     

    		    

    Br

    SiO3-2

    (show formal charges on atoms and any resonance structures)

     

     

     

     

     

     

    		    

    Si

     

    XeO3

     

     

     

     

     

     

    		    

    Xe

    PCl3

     

     

     

     

     

     

    		    

    P

     

     

  15. Draw the best resonance structure for each possible structure and assign formal charges to determine whether the connectivity in dinitrogen oxide is NNO or NON. Identify the more stable structure and explain your reasoning.

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  16. Draw the compounds XeF3+ and CH2O. Explain the bonding in terms of valence bond theory. That is show the atomic orbitals on the central atom, describe any electron promotion necessary, and show the orbitals involved in both sigma and pi bonding.

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  17. (22 points) Answer the questions for the structure shown below. Note that the molecule was drawn to fit the imagination of the instructor and may not faithfully represent the geometry of the molecule. All bonds and lone pairs are shown.

 

    1. What are the molecular and orbital geometries around Xenon?

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      Molecular _____________________ Orbital ____________________

       

    2. What is the hybridization of the nitrogen atom?

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    3. What is the formal change on the fluorine atom?

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    4. What is the hybridization of carbon? Charge on carbon?

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    5. What are the orbital and molecular geometries around iodine?

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      Molecular _____________________ Orbital ____________________

       

    6. What is the hybridization of the bromine atom?

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    7. What are the orbital and molecular geometries around oxygen?

 

Molecular _____________________ Orbital ____________________