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Posts posted by anthropos

  1. "Treatment of 3-methylcyclohexene with HCl yields 2 products, 1-chloro-3-methylcyclohexane and 1-chloro-1-methylcyclohexane. Draw a mechanism to explain the result."


    I can't really figure out one can arrive at 1-chloro-1-methylcyclohexane, how did the positive charge manage to shift to the CH3 position?


    Also, I read another textbook, and it features a question which states that "reaction of HBr with 3-methylcyclohexene yields a mixture of four products:

    cis- and trans-1-bromo-3-methylcyclohexane and cis- and trans-1-bromo-2-methylcyclohexane". Then shouldn't the HCl reaction yield products of similar structure?


    Thank you.

  2. Q: The central mechanical component in automobile engine is a piston-cylinder assembly, which allows the working fluid to function properly. Consider such an assembly with air as working fluid. The cross-sectional area of the piston is 0.1 m2. Initially the piston is at 1 bar and 25 C, 10 cm above the base of the cylinder. In this state, the spring exerts no force on the piston. The system is then reversibly heated to 100 C. As the spring is compressed (the spring is connected to the top of the piston), it exerts a force on the piston proportional to -kx, where k = 50000 N/m and x is the displacement from its uncompressed position. Air is assumed to behave as ideal gas. The atmospheric pressure is 1 bar. Determine the work done. (-166 J)


    I would like to ask, how is the heating "reversible"? The pressure of the system (gas) should increase, since the spring is being compressed, that means the force of the spring exerted on the piston is increasing and thus so should the counter force from the gas pressure. Here the temperature also increases, and so does the volume of the system. So it's not isobaric, isothermal, isochoric, right? I am stuck. i don't understand how it can be reversible, and what equations I can write out to start out solving the problem.


    Also the heat to the system, does it equate to work done by gas and heat lost? SInce the second law states that you can't convert all heat to work.


    Please explain thanks!

  3. I have difficulty understanding the Pxy diagram of a binary system (e.g. an ideal benzene-toulene mixture) and some facts in general, have been stuck there for hours, reading notes and everything but never seem to find or understand it.


    1) Why is the bubble point line the line that indicates the total pressure of the system (partial pressure of benzene and toulene vapours)?


    2) Why is the dew point curve and how do I derive it, because I really have no idea.


    3) When I say a liquid is saturated, it means it's in equilibrium with the vapor, or is it 100% liquid. Then this means the vapor is saturated as well? But there is a graph with P against specific volume that depicts a maximum curve, one of the two sides being the saturated liquid line, and the other being the saturated vapour line and they are not together.


    Gah please help thanks, I am dying to know. :confused:

  4. The MATLAB website states that "the number of arguments is negative if the function has a variable number of arguments" when I use nargin to test such functions.


    So when I enter nargout ode45, I get -5. But why is the absolute value 5, does that mean it's the maximum number of outputs that ode45 can release? It is not a random number because I keep getting the same result after typing in.


    Does anyone know why this is happening? Thank you :D

  5. Haha, actually I am a bit confused by what you have said. But I sorta guessed you meant something like configuring, and I didn't know how to configure my compiler until i accidentally went to some website and i solved the problem. Thanks a lot :D!!!


    And yes I think I am that sort of person who will find programming fun!

  6. I wrote the following program 01.cpp:


    //My first program

    #include <iostream>


    int main()


    std: :cout << "Welcome to C++! \n";

    return 0;



    The file iostream.h is under C:\Borland\bcc55\Include\iostream.h, while the program is saved under C:\Borland\bcc55. I thought an .exe file was created after doing the following in Command Prompt on Windows.


    See Picture.



    cpp32.exe is under C:\Borland\bcc55\Bin\. I included C:\Borland\bcc55\Bin\cpp32.exe under Path in the Environment Variables under Advnaced section of COntrol Panel, so I can call it out anytime.


    But my exe file is not created. Instead I get an .I file, and I don't know what it is :doh: What happened? What went wrong?


    Sorry this is my first attempt at learning programming, so the way I describe the program may not sound appropriate. Sorry.


    Thanks in advance!

  7. A bucket of water is swung in a vertical circle. Explain qualitatively why the water in the bucket does not fall out.


    My model answer then explained that


    If the speed of the rotation is high enough, the weight of the water alone in the bucket is not enough to provide for the centripetal force required. A force will be exerted by the bottom of the bucket on the water for the water in the bucket to continue to move in a circle. By Newton's third Law, the water pushes against the bottom of the bucket and thus stays in the bucket.


    What does the bold text really mean? So what happens if the weight of teh water alone in the bucket is just enough? And if my speed is not high enough, the water flows of the bucket, and what does that mean? Sorry I am really confused. Can somebody clear my confusion? :confused:


    Thanks :D

  8. I was looking for some old stuff for my mum through the mess in my storeroom when my finger was drenched in what I later found to be 2-year-old battery leakage. And my finger had an open wound. I washed it off immediately. Will it pose any hazard to my health? Because my mum's uh freaking out a bit lol.:doh:

  9. Initially these blocks of each mass m are at rest. The tabletop and pulley does not induce friction. So when the system moves, does it accelerate at g? Do both blocks have an acceleration of g? Does the weight of the top block affect the acceleration or exert a force on the bottom block? My book says 5 ms-2 and i am puzzled.



  10. easiest to hardest: physics, chem, bio


    i hate the deducing questions in chem -.- The question can assume a compound with carboxylic, amide and all kinds of functional groups and then state the observations seen after dunking them into a dozen respective chemicals and tell you to deduce the unknown compound from all the observations made. It kills -.-


    i think physics is relatively easy but still i get Bs all the time.


    i never take bio. anything you don't study will seem daunting lol.

  11. hello. I am deciding on a major. My A-level subjects are physics, chemistry, math (and chinese literature LOL) and my chem is in the A-B range. But i never went for any research programme, so will it be hard to cope if i take chem engineering?


    um, and which ChemEng programme is better, Cambridge or UCL?


    Thank you.

  12. Im having a hard time deciding on a major. ... I wanna be in a field of invention and creation. ... I'm not talking like creating a better q-tip , I mean building the impossible...


    That sounds ... well ... impossible.


    ... or creating something never thought of before.


    I can almost assure you that the number of people thinking about improving q-tips is way lower than the number of people fantazising about black-hole based time machines.


    Haha. I thought that was rather amusing. In the end most agree that he should be in engineering, like mechanical engineering. I agree too. :D

  13. um in US and UK are there any universities that are relatively good in chemical engineering? (I know universities like Purdue and Columbia are renowned for its engineering faculties but I am not very confident if I can get in because I don't expect much from my SAT and A-levels).


    uh, and one side question, is the uinversity of chicago selective?


    thanks. =) I am a bit clueless.

  14. I managed to solve the problem by using a Venn diagram. How do you do it by the Baye's Theorem? I tried but I keep getting the same equations. :confused:


    Thanks for your help! :) Haha I need somebody to help my Probability and P and C. I tend to um be rather bad at the logic stuff.

  15. Two friends Jane and Mary often do their shopping on Saturday afternoons. If Mary goes shopping, the probability that Jane also goes is 0.96. If Jane goes, the probability that Mary also goes is 0.8. The probability that neither goes is 0.07. Find the probability that both go shopping.


    How do I approach the question? I tried to do conditional probability by doing all the fractions with eg. R(Jane goes intersect Mary goes)/P(Mary goes) = 0.96 and a couple of these but didn't really work.

  16. 1) Out of 90 tins, 24 contained corns, 12 contained beans, 36 contained peas and the rest conatined mushrooms. Find the probability that Sean will have to open more than 2 tins before he finds one which does not contain baby corns.


    I am not very sure how to tackle this question. I thought of using complement, but I don't know what is the eact opposite of this situation. Actually I don't really understand what the question means.

    The answer was 0.069.


    2) A box contains 6 black balls, 4 red balls and 2 yellow balls. 3 are drawn with replacement. Calculate the probability that all 3 balls are of the same colour.


    Why isn't it (0.5)^3 x (1/3)^3?

    The correct answer was 1/6.


    3) What is the probability of getting all three cards being red out of a ordinary pack of 52 playing cards?


    Why isn't it (26/52)x(25/51)x(24/50)?

    The correct answer was 0.125.


    Please help me understand where I am wrong! I have been constantly making mistakes like that :doh:, but I don't know what is my error in thinking. Thank you!

  17. When phenol reacts with liquid bromine, three products, 2-bromophenol, 4-bromophenol and hydrogen bromide are formed.


    When phenol reacts with aqueous bromine, 2,4,6-tribromophenol and hydrogen bromide are formed.


    So what is the role of water in the second reaction of creating a trisubstituted phenol? Is there something to do with intermolecular hydrogen bonding between the OH of the phenol and the water? Why is it not usually included when drawing chemical equations for the second reaction?


    Thank you. =)

  18. What properties do sulfur particles possess that allow them to reflect the sun's rays back to space, like those in the 1991 Pinatubo eruption? I couldn't find websites that have this information =.=. (Must have been my very bad research skills)


    Is black carbon another aerosol that can reflect light besides acting as cloud condensation nuclei? Many sources keep citing sulfate particles without black carbon particles as aerosols that can encourage global dimming.


    Please help me out here! Thank you =).

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