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  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    7,760 posts since May '05
    • Originally posted by Flying grenade:

      One of my teacher  say that the reason why H- cannot reduce alkene is because alkene C=C bond is neutral(i.e. not polar)

      All along i was under this impression. 

      Today,  another different teacher say the reason is because the lone pair on H- repels with the pi e-cloud of C=C bond

      :/ i am flustered 


      See if you're intelligent enough to see how the following Singaporean link explains the answer to this H2 Chemistry question.

      http://mothership.sg/2016/05/wear-white-movement-to-be-held-on-the-same-day-as-pink-dot-yet-again/

      Whether you get it or not, don't post further on this topic on this forum, don't spoil the fun for others! *evil laugh*

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    7,760 posts since May '05
    • Originally posted by Flying grenade:

      Why is Mno4- a stronger oxidising agent compared to Cr2O72-?


      Because of a complex combination of reasons, which you needn't worry about for A levels. Most relevantly, the oxidation state of the heteroatom in the oxidizing agent (ie. +7 versus +6), but also the electronegativity, the charge density, the electron affinity enthalpy, hydration enthalpy, electron configuration, reaction mechanism, etc.

      So when you explore these issues at Uni level, you'll realize there are no longer any short, simple answers (those are the O level days of naivety), but a beautifully complex balance of separate (and oftentimes opposing factors). A levels is a transition state or intermediate between naively simplistic O levels, and beautifully complex Uni levels.

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    7,760 posts since May '05
    • Originally posted by Flying grenade:

      Pang cheng cheong's book and my school cher say reaction of carbonyl cpds with 2,4dnph is at r.t. , but cs toh book say heat, and making sense's reagent and conditions say need warm!

      How??? These reagents and conditions makes me damn f**king agitated!

      Idk but this is one of my thought 24dnph reaction(condensation/nu sub) can be carried out under r.t. But perhaps warm, accelerates the reaction , right? So both are acceptable. My doubt, would cambridge mark both correct?? If i write heat will they know cos i know the reaction will be quicker? Or will they think i am dumb , the reaction requires heat to overcome Ea of reaction? So write 24dnph, r.t. more safe is it?


      Allow BedokFunland JC to enlighten thee :

      As far as 2,4-DNPH is concerned, Cambridge doesn't give a flying f**k whether you write "room temperature" or "warm" or "heat" or even if you don't specify the temperature at all.

      However, don't mistake Cambridge's kind reasonable tolerance for weak bochup nonchalance : between PCl3 and PCl5, you *must* specify "heat" for 1 of these reagents, or Cambridge will penalize you. If Cambridge asks you to explain why this difference, do you know how to answer?

      (let's hope for more such out-of-the-box questions for this year's and all future Singapore H2 Chemistry papers, shall we? That will shut up those armchair critics who take perverse pleasure in criticizing the entire Singapore education system to be all about blind memorization without deeper understanding... such criticism applies more for PSLE, N and O levels, but less so for A levels and certainly not Uni levels; and among A level subjects, such criticism is even less valid for Chemistry than other A level subjects, hopefully Cambridge will continue this trend for Singapore's H2 Chemistry).

      Edited by UltimaOnline 24 May `16, 5:29PM
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    7,760 posts since May '05
    • Originally posted by Flying grenade:

      One of my teacher  say that the reason why H- cannot reduce alkene is because alkene C=C bond is neutral(i.e. not polar)

      All along i was under this impression. 

      Today,  another different teacher say the reason is because the lone pair on H- repels with the pi e-cloud of C=C bond

      :/ i am flustered 


      See if you're intelligent enough to see how the following Singaporean link explains the answer to this H2 Chemistry question.

      http://mothership.sg/2016/05/wear-white-movement-to-be-held-on-the-same-day-as-pink-dot-yet-again/

      Whether you get it or not, don't post further on this topic on this forum, don't spoil the fun for others! *evil laugh*

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    7,760 posts since May '05
    • Originally posted by Flying grenade:

      Why is Mno4- a stronger oxidising agent compared to Cr2O72-?


      Because of a complex combination of reasons, which you needn't worry about for A levels. Most relevantly, the oxidation state of the heteroatom in the oxidizing agent (ie. +7 versus +6), but also the electronegativity, the charge density, the electron affinity enthalpy, hydration enthalpy, electron configuration, reaction mechanism, etc.

      So when you explore these issues at Uni level, you'll realize there are no longer any short, simple answers (those are the O level days of naivety), but a beautifully complex balance of separate (and oftentimes opposing factors). A levels is a transition state or intermediate between naively simplistic O levels, and beautifully complex Uni levels.

  • lucyll's Avatar
    10 posts since Nov '14
    • It's always the case that you or the person who borrows your phone might have pressed the delete button inadvertently or you could have made it happen by squeezing the phone when laying it inside your pocket. There're also strong possibilities that your text messages have been erased by erroneous operation of the system itself, your phone has been formatted or attacked by unknown, severe viruses, you have restored the factory settings, or your messages have been replaced by new ones due to the phone's capacity of containing only a limited number of messages.

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      Watch this youtube video to know more:

      https://www.youtube.com/watch?v=44anBzJHRp0

  • Dustydress's Avatar
    2 posts since May '16
    • Thousands of candles can be lighted from a single candle, and the life of the candle will not be shortened. Happiness never decreases by being shared. - Buddha

  • SBS3004X's Avatar
    2,428 posts since Jan '14
    • Originally posted by SBS8478D:

      Cameo 23/5
      SBS7433P 168(BNDEP 196)

      SBS7433P is not in BNDEP.

  • SBS3004X's Avatar
    2,428 posts since Jan '14
    • Originally posted by SBS6853S:

      not always true leh... for serangoon, newbie services are not 315 and 317, but however are 103 and 158

      315 trips always very long... The bus sometimes takes 10 full minutes to loop at Serangoon North Ave 4/5 in AM Peak!

  • Flying grenade's Avatar
    365 posts since May '15
  • Flying grenade's Avatar
    365 posts since May '15
    • Idk but this is one of my thought 

      24dnph reaction(condensation/nu sub) can be carried out under r.t.

      But perhaps warm, accelerates the reaction , right?

       

      So both are acceptable. 

      My doubt,  would cambridge mark both correct??

      If i write heat will they know cos i know the reaction will be quicker? Or will they think i am dumb , the reaction requires heat to overcome Ea of reaction? 

       

      So write 24dnph, r.t. more safe is it? 

  • SBS3004X's Avatar
    2,428 posts since Jan '14
  • Flying grenade's Avatar
    365 posts since May '15
  • Flying grenade's Avatar
    365 posts since May '15
    • Pang cheng cheong's book and my school cher say reaction of carbonyl cpds with 2,4dnph is at r.t. , but cs toh book say heat, and making sense's reagent and conditions say need warm 

       

      How??

       

      These reagents and conditions makes me agitated !

  • Dustydress's Avatar
    2 posts since May '16
    • We are shaped by our thoughts; we become what we think. When the mind is pure, joy follows like a shadow that never leaves. -Buddha

       

       

  • Teronyongzhi's Avatar
    1 post since May '16
  • Queen of sgForums
    驚世駭俗醜不啦嘰 moderatress
    FireIce's Avatar
    257,170 posts since Dec '99
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    113,578 posts since Dec '03
  • Queen of sgForums
    驚世駭俗醜不啦嘰 moderatress
    FireIce's Avatar
    257,170 posts since Dec '99
    • Get a free beverage when you download and install the free McCafe Devotee App till 20 June 2016

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  • lemon1974's Avatar
    8,374 posts since Dec '04
  • DiscoPiggy's Avatar
    4 posts since May '16
    • Yeah totally possible.  I got 10 days for Epilasik, a week for chicken pox and 3 days for wisdom tooth extraction.

      But if you are referring to more 'common' ailments, generally you gotta ask the doctor for it. Have done so for gastric flu and very bad food poisoning, and the doc was kind enough to grant my request :)

  • DiscoPiggy's Avatar
    4 posts since May '16
    • On a daily basis - indulge in some sports (i.e. running, swimming, cycling, yoga), play video games, take a nap, watching anime/drama... at no cost.

      Occasional treats to myself - deep tissue massage ($50), facial ($60), overseas trip ($-varies depends location & duration)

  • DiscoPiggy's Avatar
    4 posts since May '16
  • DiscoPiggy's Avatar
    4 posts since May '16
    • 1 million?  Your are talking about SGD right?  USD or Euro, even better!

      There was a time that I'd say no way I'm gonna give up playing WoW no matter how much you pay me... but now that I'm (slightly) older, with more "responsibilities", I'd say yes.  I can do alot with S$1m.  Actually I would take S$5k even, if it were offered to me, to ditch my favorite game for a year.

      That doesn't mean I can't play other games, right? 

  • TPS Timothy Mok's Avatar
    669 posts since Aug '07
    • SBS Transit 68

      Pasir Ris Drive 3

      Pasir Ris Central

      Pasir Ris Drive 8

      Tampines Avenue 12

      Tampines Avenue 9

      Tampines Avenue 7

      Tampines Central 7

      Tampines Avenue 6

      Tampines Avenue 9

      Tampines Avenue 10

      Tampines Avenue 5

      Tampines Avenue 8

      Tampines Avenue 3

      Tampines Avenue 4

      Bedok Reservoir Road

      Bedok North Avenue 3

      Bedok North Street 1

      Chai Chee Street

      Chai Chee Drive

      New Upper Changi Road

      Chai Chee Road

      Chai Chee Street

      (and return back to the normal routing)

      - to bypass Tampines MRT and Bedok MRT.

      - to provide connectivity to Tampines West MRT & Bedok Reservoir MRT.