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Kap #4

Discussion in 'MCAT Discussions' started by xoomn, Aug 7, 2002.

  1. xoomn

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    I just took this things and man was it tough. I was wonder if anyone is welling to answer a few question i had in the PS section.

    Q84. How did they come with the answer?
    Q95. How do you do this thing. I have totally had gone blank on this one. I mean, I did not know where to start.
    Q98. Is this info we have to know which I don't or is it in the passage and I'm not able to decipher?
    PVI. I got only Q100 correct and missed the rest. How do you solve these problems?

    Q109. Is there a formula for Potential Engery and separation distance b/c if there is I don't know of any.
    Q112. Did not follow there logic. How can they conclude that the length would decrease.

    Q118. How can the structure of SO2 and NO2- be the same? I just dont' get this.
    PIX. I just did not understand this passages and missed half the question.
    Q129,130. Some please explain why and how they came up with these answers.

    I know that I am asking a lot but you don't have to be very detail. Just a line or two would greatly help. Thankx... :clap:
     
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  3. conure

    conure Master Distiller

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    I will take a stab at this but you should review the answers and explanations at the test center or online

    84: not to sure someone else can get this one.

    95: Pretty straight forward. Take the final AgCl obtained and divide by MW (144). This gives you moles of AgCl and b/c its 1:1 then this is also the moles of Cl. (.0027) take this and multiply by the MW of Cl- (35) this gives you the moles of Cl- obtained. Now divide this by tthe original mass of the sample (.20) and multiply by 100 to get %. (43%)

    98: I figured this was b/c solid silver is gray and this makes sense with the photodecomp info given. Also all of the other answers are way out there or are totally unfounded or unknowable.

    PVI is all about torque, most of this can be answered using concepts and no calcs. necc.

    101 if the M becomes - then the restoring force tips the boat up side down. Its not D although I think this is tempting because at torques is a minimum then M is 0 b/c theta is 90. But its not upsidedown.

    102 take equation 1 and the buoyant force equals the weight of the water displaced (mg) substitute this in and solve for water mass and you get answer B.

    103: I missed it but it makes sense. Newtons third law (equal and opposite reactions) coupled with the gravitation law. Gives anser C. the earth attracts the boat, the boat attracts the earth.

    104 if you draw out a free body diagram I'm sure you will see that the restoring force opposes the net force (C) so the answer is B.

    109: No equation neccessary. This is the potential energy graph for any two molecules coming together or separating. PE drops to the lowest at the optimal bond length and then approaches zero as separation increases.

    112: Not totally sure but I think its as the speed decreases and the frequency stays the same then the wavelength must decrease. As a result the length decreases? No I'm not sure on this.

    118: Ah yes. Well draw lewis structure for SO2 with 18 electrons the S has no formal charge and an expanded octet of ten this gives a bent geometry. NO2- also has 18 electrons with a lone pair on N with three bonds (no formal charge). A double bond to an O and single bond to the other O (-1 formal charge) gives a bent structure.

    PXI I didn't get this passage either. other than 122, mostly I left this passage to the end and didn't have time to get to it. I have no desire to do it now either. 122 is application of the right hand rule but because it is an electron all is reversed.

    129: Is similar to 95 in that its just dimensional analysis. the answer is D 4:1. 1mole of O2 ( in reaction 2) gives 2 moles of MnO(OH)2. 1mole of MnO(OH)2 to 1mole of Mn(SO4)2. 1 Mn(SO4)2 to 1 mole of I2. Finally 1mole of I2 to 2 moles of S2O3. This is how I did it you could do it backwards or whatever, someone else may know a quicker way.

    130: This is tough I went through every reaction to find one that gave me a positive EMF (galvanic cell). To do this you must find 2 half reactions for each answer and determine EMF luckily the answer is A so you find it pretty quick. But boy was this a sh&&tty take on electrochem.

    All in all I thought the physical science on this test sucked. I didn't do to well because I ran out of time and panicked. If you look at the scoring chart curve for test 4 and test 3 you will see that the raw score differences between the two are 3-4. This indicates it is a harder test. Make sense?

    Take care.
     

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