Homework and study help thread

Discussion in 'The Pavilion' started by pak_fan_4_life, Feb 19, 2013.

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  1. hussain.r97
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    hussain.r97 Youngsta Beauty

    May 29, 2013
    391
    Quick math question. Partial fractions.

    When you have a partial fraction with a quadratic on both top and bottom, what's the general rule?

    I thought it's just A/(x-a) + B/(x-b).

    However the mark-scheme thought differently, and added in a constant. So it looked like this -

    A + B/(x-a) +C/(x-b)

    Help?
     
  2. SOPL
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    SOPL Talented

    Jun 4, 2013
    2,706
    What's the exact equation?
     
  3. PakistanZindabad!
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    PakistanZindabad! Cornered Tiger

    Sep 29, 2012
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    Lool we just did them today. Not hard at all
     
  4. Donal Cozzie
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    Donal Cozzie Tracer Bullet

    Nov 4, 2014
    7,204
    Literally the only thing I liked about chemistry was the s,p,d orbital sections.

    Everything else was unforgivably awful and hateful, screw chemistry,
     
  5. PakistanZindabad!
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    PakistanZindabad! Cornered Tiger

    Sep 29, 2012
    10,448
    Chemistry is the best subject along with Maths. English and History are insufferable
     
  6. Don Corleone
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    Don Corleone Kaptaan

    Jul 20, 2012
    29,473
    Give me English(Norwegian in my case) and History over Chemistry, Maths and Physics any day. Can get a good grade with my eyes closed on the former, have to work for the latter :p
     
  7. PakistanZindabad!
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    PakistanZindabad! Cornered Tiger

    Sep 29, 2012
    10,448
    Complete opposite for me, I had to suffer through hours of work for history to get an A. English was Allah's blessings lol, but sciences and maths were much easier for me
     
  8. hussain.r97
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    hussain.r97 Youngsta Beauty

    May 29, 2013
    391
    A level chemistry

    Can someone help me out with electrophiles and nucleophiles?

    Could I have a good definition of both, and please tell me how to identify each.

    Why are Br- and Cl- electrophiles rather than nucleophiles?

    I kind of get it, but I need to confirm.
     
  9. hussain.r97
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    hussain.r97 Youngsta Beauty

    May 29, 2013
    391
    Sorry, for late reply. I understand it now. Do you still want the question? ;)
     
  10. Reverse Swing
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    Reverse Swing Talented

    Jul 30, 2013
    1,559
    I only did this about 15 months ago but trust me I hardly remember a single thing.

    Electrophile is an electron lover...thats all I remember.

    By the way for definitions I think the specifications may help.
     
  11. hussain.r97
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    hussain.r97 Youngsta Beauty

    May 29, 2013
    391
    Did this last year too, it's part of A2 as well as AS, but I need to refresh myself.
     
  12. SOPL
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    SOPL Talented

    Jun 4, 2013
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    An electrophile is a species which is electron-deficient and thus attracted to electrons. Contrastingly, a nucleophile is one which is attracted to positively-charged species and one which is an electron pair donor, with which it can donate a lone pair to form a bond.

    And as far as I know Br- and Cl- are nucleophiles, rather than electrophiles. They are electron pair donors.
     
  13. hussain.r97
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    hussain.r97 Youngsta Beauty

    May 29, 2013
    391
    Apparently bromine can be an electrophile too?

    http://www.chemguide.co.uk/mechanisms/eladd/symbr2tt.html

    From what I get, Bromine is easily polarized, and thus, has the ability to form electrophiles too.

    How is it easily polarised?
     
  14. SOPL
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    SOPL Talented

    Jun 4, 2013
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    The negatively-charged Br- ion which is formed during the intermediate stage is not a electrophile; it contains a lone pair of electrons with which it can form a bond with an electron-deficient atom.

    But, the positively-charged Br+ ion which is effectively formed during the initial stage of an electrophilic addition reaction is indeed an electrophile, as it has an electron-deficiency.

    Basically, when the Br-2 (sorry, no subscript possible) molecule approaches the double bond of an alkane, the electrons in the pi bond repel the electrons in the bond between the two Bromine atoms in the Br-2 molecule, such that one Br atom becomes slightly (delta) positively-charged and the other slightly (delta) negatively-charged.

    In effect a dipole-dipole bond is induced (bond in which one atom has a greater attraction to the electrons to the other) and from there the electrons in the pi bond can attract the slightly-positively charged Br atom.

    Did I explain it well enough?
     
  15. PakistanZindabad!
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    PakistanZindabad! Cornered Tiger

    Sep 29, 2012
    10,448
    I have a question where the equation was
    f(x)=2x^2-6x+5
    And I needed it in form
    a(x+b)+c
    So I did that and it was
    2(x-3/2)^2+1/2
    And that's right according to the answers, but how do I deduce the minimum value from this? It's 1/2 but idk why, is it just the value of C?
    @SOPL @Reverse Swing
     
  16. SOPL
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    SOPL Talented

    Jun 4, 2013
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    @PakistanZindabad!

    2*(x-3/2)^2 + 1/2 is the right answer.

    You probably know that the minimum value of an x^2 graph occurs when x = 0 (think about it, both negative and positive values equate to positive values when squared).

    To get the bracketed squared part of the equation to be 0 (the lowest value possible for square numbers as both -ve and +ve numbers are >1 when squared), you'd need to input a value of x = 3/2 in this case. 0^2 *2 is still 0 and therefore the minimum value must be 1/2 because that 0 +1/2 = 1/2.

    Understand?
     
  17. Momo
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    Momo Emerging Player

    Mar 2, 2012
    557
    The minimum value is not 1/2. It's 3/2. You get it by differentiating the original equation, putting it equal to zero and solving for x.
     
  18. SOPL
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    SOPL Talented

    Jun 4, 2013
    2,706
    I think he meant the minimum value for the y-coordinate rather than the x.
     
  19. Momo
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    Momo Emerging Player

    Mar 2, 2012
    557
    Yes that is 1/2 indeed. Putting x=3/2 (obtained from the differentiation) into the original equation would yield f(x)=1/2.
     
  20. SOPL
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    SOPL Talented

    Jun 4, 2013
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    What degree did you undertake at Uni (if you attended and don't mind me asking), @Momo? Your posts come across as a history/classical studies/philosophy kind of guy.
     
  21. PakistanZindabad!
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    PakistanZindabad! Cornered Tiger

    Sep 29, 2012
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    Awesome, thanks! Thanks @Momo too
     
  22. Reverse Swing
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    Reverse Swing Talented

    Jul 30, 2013
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    Sorry I'm not ignoring you...for some reason I don't receive a notification when I'm tagged.
     
  23. PakistanZindabad!
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    PakistanZindabad! Cornered Tiger

    Sep 29, 2012
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    Lool np it's all good
     
  24. hussain.r97
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    hussain.r97 Youngsta Beauty

    May 29, 2013
    391
    Thanks! I got it. So basically, the double bond in an alkene is electron rich, and hence repels electrons in Br2, polarizing it, making it act as an electrophile when it splits?
     
  25. SOPL
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    SOPL Talented

    Jun 4, 2013
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    Essentially, yes. Because of how the pi bond is formed (less secure than the sigma/single bond), it repels the electrons in the bond between the two bromine atoms in Br-2 to one side of the atom, giving the close (if you imagine the Br-2 atom approaching vertically to the vertically aligned alkene) a delta positive charge and the other a delta negative charge.

    The delta positive charge is thus attracted to the electron-rich area and one carbon (observing Markovnikov's Rule - not sure if it's on your spec) therefore uses both electrons from its pi bond to bond with the delta positively charged bromine atom. The fully negatively-charged Br- ion that is formed during the intermediate stage is a nucleophile as it has a lone pair of electrons and is attracted to positive spheres of charge due to it's negative charge.

    Sorry for the long post, lol.
     
  26. hussain.r97
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    hussain.r97 Youngsta Beauty

    May 29, 2013
    391
    Hey. If anyone has the time, could you take a look at this Classical Studies practice essay I wrote. Just give me some comments, and a mark out of 25. Would be much appreciated, thanks.
    It follows this Mark Scheme in case you're curious - (see page 3) - http://papers.xtremepapers.com/CIE/C..._w13_ms_11.pdf

    @Don Duckman

    Does Alexander deserve to be called Alexander ‘the Great’?

    Greatness is something that has been attributed to many people over the course of history; many of these people were great enough to be titled ‘the Great’. All of these people are great for one reason or another, but they all have one thing in common, they have a legacy that has lasted for eternity. Of all the ‘Greats’, deservingly or not, Alexander III of Macedon is the most celebrated.

    Alexander is most renowned for his conquest of the Achaemenid Persian Empire, the greatest empire known to man, an undoubtedly tremendous feat. However, his empire only lasted for as long as he lived, it fell apart upon his death. This did not destroy his legacy, for centuries after his death his territory was ruled by various Greek states, bringing the influence of Greek culture to Asia throughout the Hellenistic age and beyond.

    Although indirectly; Alexander had a massive influence on the course of Iranian and Egyptian history for centuries after his death. The fact that his actions were still influencing the world so far after his death is indeed remarkable. His influence did not stop there; many rulers and generals over the course of history have looked at Alexander for inspiration, even 1000 years after his death. This included rules such as Napoleon Bonaparte.

    What really made Alexander stand out was the fact that he was not just a conqueror. Many people in history have been conquerors; great military leaders and strategists who knew exactly what to do on the battlefield, but had little knowledge of how to functionally run a country. Alexander was different. He was a brilliant military commander, strategist, and soldier; which is proven throughout all four of his major battles, where he was vastly outnumbered by the enemy, but he won due to sheer leadership and strategic thinking, Alexander had the ability to read the situation extremely well. On top of this, he knew how to run his empire, and keep his people happy. Alexander knew that the only way forward was through unity.

    Alexander was not new to this idea of uniting his nation; after the death of Philip, the Greek states under the league of Corinth rose up for independence. Alexander successfully reunited and calmed the Greeks through war and diplomacy. He destroyed Thebes, which while sounding barbaric, actually sent a message to the rest of Greece. His treatment of Athens was however very different. When Athens refused to hand over leaders of the revolt to Alexander, instead of destroying or fighting Athens, Alexander let them be. This is a display of Alexander’s intellect and cunning. Making Athens his enemy would make Greece his enemy, and Alexander did the smart thing by working towards bringing Athens on his side, and continuing to please them throughout his campaigns.

    Throughout his campaigns, Alexander does many acts in a bid to unite and please his subjects. In Asia Minor, he instates democracy; while in Egypt and Babylon he orders the rebuilding of temples and also sacrifices to the Apis bull in the former. All these acts are to keep his subjects happy, and on his side, a very intelligent move, and something a ‘warmonger’ wouldn’t even consider. The only issue with Alexander’s administration was the fact that he was away campaigning for so long that everything he set up fell apart, because he was not there to run his own empire.

    Alexander went further than just pleasing his subjects, in a bid to bridge the gap between Eastern and Western cultures, he introduced the policy of fusion. This involved intermarriage, wearing Iranian clothing, and adopting Iranian culture. This included the controversial ‘proskynesis’. Overall, fusion was another smart move by Alexander, as this would theoretically increase tolerance and unity amongst the people. However, introducing proskynesis to the Macedonians and Greeks was unwise due to the fact that people of Greek origin view prostration as something only done in front of gods, while Persians thought differently. Prostration was completely against Greek ideology, and caused outrage among many of Alexander’s companions.

    Though Alexander achieved much greatness, he was not without his flaws, and he committed many acts that are not associated with a great, honourable man. Especially towards the end of his life, Alexander development a serious drinking problem, this often led to anger, rage, and loss of control. He ended up killing Cleitus the Black, one of his best friends, in drunken rage, which is a truly despicable act. What is more worrying is the fact that when he tried drawing his sword, someone had already taken it off him, which shows that this was a recurring issue. It is said by Diodorus that Alexander burnt down the palace of Persepolis, drunk, because he was spurred on by a woman in his court who said it would be his greatest achievement. Whether it is true or not, burning down the palace of Persepolis was an unwise and dishonourable act.

    Despite his developing bad habits, and increase in status, Alexander never ceased to look at his men as equals, and he always interacted with them the same way he always did. The greatness of Alexander is comparable to Cyrus the Great, the founder of the Acheamenid Persian Empire. Cyrus is very similar to Alexander in every positive way. Cyrus united Iran, conquered Babylonia and Lydia, and is known for his work in human rights. He is seen as a liberator of people, and he holds a high place among Jews, even appearing in the Old Testament. Among all these similarities, both of them have a legacy that will last for eternity.

    Alexander the Great has undoubtedly tremendous achievements. Conquering the greatest empire known to man is no small feat. Alexander certainly had his flaws, but he was a human being, and no human is without their flaws. His brilliant military ability and his bridging of Eastern and Western cultures is what defines him; it is what allows him to leave his legacy. The fact that he has an everlasting legacy; and his influence reached people millennia after his death is testament to the fact that he is Alexander ‘the Great’, and deserves to be so.
     
  27. Don Duckman
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    Don Duckman Tracer Bullet

    Apr 7, 2014
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    It's good. Try not repeating words (many, throughout,...) and maybe mention more about his military genius (eg the hammer and anvil technique).
     
  28. hussain.r97
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    hussain.r97 Youngsta Beauty

    May 29, 2013
    391
    Thanks! So what would you give it out of 25?
     
  29. hussain.r97
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    hussain.r97 Youngsta Beauty

    May 29, 2013
    391
    Could someone go through this with me. A Level Chemistry, thanks!

    [​IMG]
     
  30. hussain.r97
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    hussain.r97 Youngsta Beauty

    May 29, 2013
    391
    ^ I got (i) and (ii)

    Not quite sure how to do the rest though.
     
  31. hussain.r97
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    hussain.r97 Youngsta Beauty

    May 29, 2013
    391
    ^Uhhh, actually nevermind, I got it all now. :D
     
  32. Munna
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    Munna Moderator-e-Aala

    Oct 4, 2014
    28,487
    Dayumn... even after more than a decade, Chemistry still makes me nauseous :confused:
     
  33. Passionate Pakistani
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    Passionate Pakistani The Don

    Jun 10, 2011
    68,367
    It was very annoying for me to memorize all those reactions lol and tbh I dont understand the need of studying chemistry, physics etc subjects when you aren't going to take them as a career.

    Thank God the trend is changed now.. before it was either medical or engineering or you would be consider a failure in life. People from south asia, in particular Pakistan and India have this obsession with medical subjects/doctors and are automatically considered as superior to others.. Pathetic classification of society on the basis of subjects you study.. and then the grading system.. that is even more pathetic
     
  34. Don Corleone
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    Don Corleone Kaptaan

    Jul 20, 2012
    29,473
    I thought Physics was worse.

    I wasted so much time and resources on Chemistry and Physics when I never had any use of them and replaced them later anyway lol
     
  35. Munna
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    Munna Moderator-e-Aala

    Oct 4, 2014
    28,487
    For me, any grading system is overrated. Good grades don't necessarily exemplify a person's intelligence.

    Esp as you said in Pakistan, all parents are expecting their children to become doctors or engineers, so majority of them don't even follow their natural instincts and talents. Then there is a big chunk of them who don't even realize what are they actually good at. Its majorly about opening the book, memorizing and cramming whatever text is in front of them, take the damn test and pray for a week to get high grades just to save face in front of their rishtedaar.
     
  36. SOPL
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    SOPL Talented

    Jun 4, 2013
    2,706
  37. PakistanZindabad!
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    PakistanZindabad! Cornered Tiger

    Sep 29, 2012
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    Chemistry=Maths>Biology>>>>>>>other subjects
     
  38. SwingNSeam
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    SwingNSeam Boom Boom

    Sep 12, 2010
    24,759
    Sthu. Bio over any/everything
     
  39. PakistanZindabad!
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    PakistanZindabad! Cornered Tiger

    Sep 29, 2012
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    Hell no, bio is too much memorising, chem is way more interesting
     
  40. SwingNSeam
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    SwingNSeam Boom Boom

    Sep 12, 2010
    24,759
    You gotta make sense out of it man. Don't need to memorize alot.
     

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