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General Chemistry - Solutions & Intermolecular Forces (HW Help)

  1. Jul 14, 2007 #1
    Hi,

    I need some help with my homework. I have three questions which I'm not quite sure which answer it is, though I give it my best try. If any one can help, it'll be much appreciated. Thanks in advance...

    Question One:
    Which of the following substances will have hydrogen bonds between molecules?
    a) (CH3)3N
    b) CH3-O-CH3
    c) CH3CH2-OH
    d) CH3CH2-F
    e) HI

    ** (e) cant be the answer becuz it doesnt have any Hydrogen Bonds (N,O,F)
    ** (a) cant be the answer becuz the N atom is by itself. H atom is attached to C atom and therefore cant bond with the N atom. Same with letter (d)

    I think the answer is c... Plez correct me if I'm wrong.

    Question Two:
    Which of the following should have the highest boiling point?
    a) CF4
    b) CCl4
    c) CBr4
    d) CI4
    e) CH4

    ** I think the answer if (a) becuz of the Hydrogen Bonding forces being the strongest of all forces and therefore has highest boiling point. Plez tell me know if this is the right answer or not and explain why - (if possible)

    Question Three
    A solution of Sucrose (sugar) in water in in equilibrium with solid sucrose. If more solid sucrose is now added, with stirring,
    a) the concentration of the solution will increase
    b) the concentration of the solution will decrease
    c) the concentration of the solution will remain same
    d) the volume of solution will increase
    e) a supersaturated solution will be produced.

    ** (c) cant be the answer becuz something is being added so it has to change - cannot remain same. I took a guess on this one and I think its letter (a). Again plz tell me if im wrong or correct. and explain if possible.


    Answers to any one or all of these questions will be greatly appreciated. Need this 3 hw probs. done by tomorrow. Again, thanks in advance.

    Regards,
    Katrina
     
  2. jcsd
  3. Jul 15, 2007 #2
    Hello again,

    Sorry to bump up this thread but plz anyone out there that can help me with this 3 or any one question(s)?
     
  4. Jul 15, 2007 #3
    I agree that the best answer for #1 seems like C. Requirement for H bonding is that there's an electronegative atom (NOF) and a H bonded to an electronegative atom... so only answer choice C has an electronegative atom (O) and a hydrogen bonded to an electronegative atom (in the OH group)
     
  5. Jul 15, 2007 #4
    And for #3, if I understood the question correctly, looking at the definition of supersaturated solution may help:

    http://www.chem.purdue.edu/gchelp/gloss/supersatsoln.html

    supersaturated solution: a solution that contains more solute than it would if the dissolved solute were in equilibrium with the undissolved solute
     
  6. Jul 15, 2007 #5

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    2: think molecular mass. 3: "equilibrium with solid sucrose" --- think, what color is George Washington's white horse?
     
  7. Jul 15, 2007 #6
    btw, for #2, in the given answer choices, there's no hydrogen bonding present.
     
  8. Jul 16, 2007 #7
    #2 the molecules are neither polar nnor possess hydrogen bonding.... van der waal forces exist as attractive forces between them......

    what does the strength of van der waal forces depend on?? from this you will be able to determine the substance with higher bp....
     
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