Gen Chem Dat?

Discussion in 'Pre-Dental' started by Beagle, Aug 2, 2002.

  1. Beagle

    Beagle Meet BEAGLE
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    Hey Everyone
    Wondering if anyone could help me out. I am having a very rough time in G CHEM

    1. Which of the following 0.15m aqueous solitions has the lowest freezing point?
    A. KCL
    B. AL2(SO4)3
    C. CH3OH
    D. C2H5OH
    E. NAOH

    The answer is B...anyone know why?

    2. The number of electrons that can have the quantum number n=4, 1=2 in a certain atom is
    A. 2
    B. 4
    C. 6
    D. 10
    E. 32

    The answer is D??? I thought it was E? can somene explain?


    3. Mg reacts with a certain element to form a compound with the general formula MgX. What would the most likely formula be for the compound formed between potassium and element X?
    A. K2X
    B. KX2
    C. K2X3
    D. K3X2
    E.KX

    The answer is A......??????? Anyone?

    4. Which gives the most basic solution when dissolved in water?
    A. H3PO4
    B. NaH2PO4
    C. P2O5
    D. N2NO3
    E. P2O5Na3PO4

    The answer is E...????

    And Sorry...one more...

    5. How many liters of 5.0 molar ethyl alcohol can be prepared by dissolving 460 grams of ethyl alcohol in water?
    A. 0.5
    B. 10
    C. 2.0
    D. 50
    E. 5.0

    The answer is A....

    Ok sorry for asking so many ?s...I am just a nervous wreck because my test is in less than two weeks..
    Thanks
    BEAGLE
     
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  3. vixen

    vixen I like members
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    ill look at them this weekend...they're making me feel sick looking at them....i hate gen chem.
     
  4. Dentalstu02

    Dentalstu02 Member
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    For #1, use Tf=Kf*m*i
    m=molality
    i=number of dissociated ions

    choice b) dissociates into the most ions (5), and the kf (constant)and m (.15) are the same for all of them. SO, since the Tf value is highest for b), the value of 0 degrees Celsius minus the Tf value will be the lowest value for b).

    For #2,

    For any n value the maximum number of electrons will be 2n^2. So this is 32 for n=4. But since L=2 also, the easy way is solve 4L+2. Which is 10. Another way to look at this is that for n=4, L will be in the range of 0, n-1. So. 0,1,2, and 3. The magnetic spin is defined as -L to L. So since L=2, ML=-2,-1,0,1,2. And lastly, each orbital has two spin orientations, +1/2 and -1/2, so there will be twice as many electrons. SO 5*2 = 10.

    I hope that these answers make sense. I can look at the others later.....
     
  5. UBTom

    UBTom Class '04 official geezer
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    Right off the top of my head, I think I can answer #3 and #5. The rest will require me to whip out my old chem textbook and review, and and I'm sure someone will have posted answers for those before I'm done. :D

    Anyway, #3 looks straightforward. If you look at the Periodic Table of Elements, you will see Mg is a Group-II element and needs two more electrons to complete its outer shell. K is a Group-I element and needs only 1 more electron to complete its outer shell. Therefore, if only 1 atom of Element X is needed to form an ionic compound with Mg, it would have two electrons to give. Since each K atom can accept only 1 more valence electron, it means you will need two K atoms to form a stable ionic-bond compound with Element X, so the answer is A: K2X.

    On to #5.... The given answer looks kind of strange. What I'm thinking is that the chemical formula for ethyl alcohol is CH3CH2OH. That means 1 mole of CH3CH2OH would weigh 46 grams. So if you make 1 liter of solution with 460 grams of EtOH, you will get a 10-molar solution. A 5-molar solution using 460grams of EtOH would then be 2 liters so my answer would be C. If the right answer is A then I need to review and see what I missed. :p
     
  6. crimson

    crimson What up Smokey!
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    For 2, know that total number of electrons for a given L is (4L+2), i.e. 10. Another way to do this is knowing that m(l) for a given L is between -L and +L. So yo have 5 orbitals with m(l) numbers -2, -1, 0, 1, 2. Now there are only 2 electrons per orbital, so you have 5X2=10 electrons.
     

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