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    Out of 250 questions, I am unsure of the following:

    1.For a given substance that exhibits liquid-crystalline properties, the transition from solid to liquid-crystal state occurs:
    a.over a range of temperatures that includes the melting point of the soild.
    b. at a well defined temperture above the melting point of the solid.
    c. over a range of temps between the melting point of the solid and the boiling point of the liquid.

    2. For a given substance that exhibits liquid-crystaline properties, the liquid-crystalline state exists:
    a. at one perticular temp above the melting point of the solid.
    b. in a range of temps above the melting point of the solid.

    3. The empirical formula of an addition polymer:
    a. is the same as that of the monomer from which it is formed.
    b. is the same as that of the monomer from which it is formed except that 2 H and 1 O have been added _or- subtracted.

    4. Which statement about polyethylene is false?
    a. it can be amorphous
    b. it is used to manufacture bottles

    5. The monomer that is polymerized to make natural rubber is?

    6. Photoionization processes (eg..N2 + hv--> N2+ + e-) remove UV of <150 nm. Which photoreaction is the prinicipal absorber of UV in the 150-200 nm range in the upper atmosphere?
    a. N2 + hv --> 2N
    b. O2 + hv --> 2O
    c. O3 + hv --> O2 + O
    d. N2 + O2 + hv --> 2NO
    e. NO + O2 + hv --> NO3

    7. The C-Cl and C-F bond dissociation energies in CF3Cl arw 339 kj/mol and 482 kj/mol, respectively. The max wavelength of radiation required to rupture these bonds are ________ and _____, respectively:
    a. 45.0 nm , 207 nm
    b. 742 nm, 654 nm
    c. 482 nm, 248 nm
    d. 353 nm, 248 nm
    e. 979 nm,, 953 nm

    8. Why does ozone not form in high concentrations in the atmosphere above 50 km?
    a. insufficient oxygen is available
    b. Atomic oxygen concentyration is too low at high altutudes.

    9. Why are CFC's so damaging to the ozone layer when they are such stable molecules?
    a. the radiation in the stratosphere dissociates them producing chlorine atoms that catalytically destraoy the ozone.
    b. they are greenhouse gases that raise the temp above the disociation temp of ozone.

    10 Cl atoms formed via phtolysis of C-Cl bonds of CFC's in the stratsphere are particularly effective in destroying ozone at these altitudes because:
    a. Ci atoms catalytically convert O3 to O2
    b. Cl atoms stoichiometrically convert O3 to O2.
    c. Cl atoms absorb UV, which generate O atoms to react with the O2 to produce ozone.
    Cl atoms react with H or N atoms, which catalyze conversion of O2 to O3.

    11. How many grams of sodium chloride are present in a 1-L sample of seawater that is 0.55 M in chloride and 0.47 M in sodium ion?
    a. 47
    b. 27
    c. 32
    d. 100
    e. 60

    12. Gasoline and water do not mix because gasoline is:
    a. less dense than water
    b. less viscous than water
    c. nonpolar and water is polar

    13.Which sunstance would be the MODT soluble in gasoline?
    a. NaNO3
    b. HCl
    c. hexane
    d. NaCl
    e. water

    14. Which statement about hydrocarbons is false?
    a. cyclic alkanes are structural isomers of alkanes
    b. alkanes are more reactive than alkenes
    c. alkanes can be produced by hydrogenating alkenes
    d. alkenes can be polymerized
    e. the smallest alkane ti have structural isomers has 4 carbon atoms.

    15. Benzene behaves diefferently from a hydrocarbon wich simply contains three C=C bonds in that the latter would be expected to react much more readily with:
    a. H2
    b. Cl2
    c. Br2
    d. HCl
    e. all of the above

    16. The general formula of an aldehyde is:
    a. R - CO - OH
    b. R - CHO
    c. R - CO - OR
    d. R - CO - R
    e. R - O - R

    Please help....Thanks...

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