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  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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    8,572 posts since May '05
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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    8,572 posts since May '05
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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    8,572 posts since May '05
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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    8,572 posts since May '05
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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    8,572 posts since May '05
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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    8,572 posts since May '05
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    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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    • [Malaysia] - Sultan of Johor, Sultan Ibrahim Sultan Iskandar, tells Dr Mahathir to "keep his mouth shut" about criticizing "Bangsa Johor".

      The Sultan said Dr Mahathir was “not qualified” to talk about unity.

      “He is going around dividing the people including the Malays, while I am uniting Malaysians of all races including the Malays,” he said.

      https://sg.news.yahoo.com/sultan-johor-tells-dr-m-073605405.html

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    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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    • Originally posted by Flying grenade:

      is the reactant CH3CH(OH)COOH?

      what does the addn of water H2O do after generating PBr3 in situ ???


      Obviously. If you don't add water, your final product will be different (hint : also look at the other parts of the molecule lah! wah biangz).

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    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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    • Originally posted by Nikkilyx:

      Hi i need some help...

      Which of the following will not reduce random errors in your experimental measurements?

      a) double the weight of magnesium used to a calorimetry experiment

      b) use a thermometer with a smaller scale

      c) use activated and finer magnesium granules

      d) use a larger calorimeter with the same volume of solution

      i am thinking the answer is d since the rest will lead me to a more precise answer


      Correcto.

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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    • [Singapore] - Singapore Ambassador-at-large Bilahari Kausikan shared the following Singaporean cloak-&-dagger story of political espionage.

      "I was then pretending to study in the University of Singapore. I did something that could potentially have had serious ramifications — what I am never going to say, so don’t bother to ask. Nobody knew what I did except my fellow conspirators — or so I fondly believed — but things began to go pear-shaped and I thought I’d better come clean before everything crashed.

      I telephoned my father, then (Singapore’s Ambassador) in Moscow. Before I could say anything on a line that like all Embassy lines was obviously tapped, my father said he knew about it and told me to tell Mr Chia. I dutifully called Mr Chia. Again before I could say anything he said he knew about it, and told me to go and meet Mr Nathan at Ministry of Foreign Affairs (MFA) which was then in City Hall, now our National Gallery.

      With more than a little trepidation, I made my way to City Hall and was tremblingly admitted into Mr Nathan’s presence. He wasn’t then working in MFA. He must have just borrowed an office in MFA to meet me as he was then in a department whose very existence a callow youth should not know about let alone visit. Again he already knew all about what in the innocence of youth I had thought was secret. Why did you do it, he demanded. I answered the best I could. Mr Nathan sat in grim faced silence, apparently pondering what I said.

      Who else was involved, he suddenly barked at me. No one I said. Don’t lie. No one, I insisted. Again he pondered in silence. I sat before him nervously for what seemed an eternity.

      Will you take responsibility, he finally asked. Exasperation momentarily overcame fear. That’s what I’ve been trying to do, I snapped.

      What’s the worst that can happen to you, Mr Nathan snapped back. I don’t know, I replied, puzzled. Will you be hanged, he asked.

      I don’t think so, I hope not, I replied, by this time thoroughly discombobulated, which I now realise was his intention.

      Mr Nathan broke into a smile — and those of you who know him should know he had a very charming smile — So what are you worried about? You did what you thought was right, it was stupid, but you won’t be hanged. Go, he said.

      I got up and made for the door. He called me back. Good that you are willing to take responsibility for what you thought was right, he said. Never evade responsibility, but if you want to play such games again, ask someone who knows how, he said. I fled."

      - Bilahari Kausikan.

      Someone commented, "I know exactly what Bilahari Kausikan did but I'm not going into details either. At the time there was a cloak-&-dagger battle of wits going on between the Pyramid club and USSU. USSU spies had caught the Pyramid club spies while they were doing some dastardly deed in the dead of night. Bila and his team got away with it because they were agents of the PAP establishment in the first place. Nathan's "magnanimity" had nothing to do with the outcome. Had the tables been turned (ie. had he been anti-PAP spying on PAP), the consequences would have been severe. I've said all there is to know about the episode. A crime was committed and he was not prosecuted. The pattern repeats itself."

      Edited by UltimaOnline 25 Aug `16, 2:48PM
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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    • Originally posted by Flying grenade:

      page 455

      example 11.14

      what's the first reaction? substitution of Br from H in Alkane?


      Typo error in the reactant. Mixing P4 and Br2 simply generates PBr3 in situ.

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    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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    • Originally posted by Flying grenade:

      page 455 

      part f

      so like proteins are soluble in water, and that's about it? wouldn't polar water "interfere with the H bonding between R groups" , as ethanol would? 


      It 'interferes' until you get your current desired configuration of proteins, supporting life specifically in aqueous environments only. Billions of years of evolution, yo.

      Of course, both Creationism and Darwinism are oversimplified and incomplete. The truth is more akin to Interventionism, and evolution continues hand-in-hand with higher guidance, at all levels. Just as human geneticists would biotechnologically intervene in the genomes of other species for various purposes of genetic modification and even creation, likewise on a macroscopic level across planetary civilizations and beyond.

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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    • Originally posted by Flying grenade:

      page 453

      addition of polar organic solvents will denature proteins

      how about inorganic solvents like water?


      Then you die liao lor. All the proteins in your body kena denature liao.

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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    • Originally posted by Fxwhy:

      MJC 2015 Prelims Paper 2 

      1e) For the safety hazard, can I write chemical reagents like ethanal are corrosive when it is in contact with the skin and eyes? 

      3a) Where did the ans get 2/4 from? I am also quite weak at approaching this type of qns where do you start?

      3d) Why doesnt the ans include bond length? How do you know when the ans requires you the write bond length or bond energy? 

      Will I be penalised if I write PCl5 at rtp instead of anhydrous PCl5 at rtp?


      Q1e) Ethanal is toxic and carcinogenic, not corrosive.
      https://en.wikipedia.org/wiki/Acetaldehyde#Toxicity

      Q3a) Instead of blindly memorizing and applying a mathematical formula, use common sense. For a uninegatively charged species : when mass is 37g, deflection is merely -1 degrees. Hence when mass is 1g (ie. much lighter), deflection should concordantly be -37 degrees (ie. larger magnitude deflected). Since mass of He is 4g, hence deflection should be -9.25 degrees (if uninegatively charged). Since He nuclei is dipositively charged, hence deflection should be +18.5 degrees.

      Q3d) Bond length here is only indirectly relevant (since bond length is inversely proportional to bond strength, ceteris paribus). It is bond strength which is directly relevant. Hence, there is no need to (ie. no marks awarded for) mentioning bond length.

      Q4ai) It's ok if you don't specify "anhydrous", as long as you do *NOT* specify aqueous (aq) (which would be marked wrong).

      Same for all reagents which need to be anhydrous, eg. LiAlH4 reducing agent, acyl halides for nucleophilic acyl substitution, Grignard nucleophilic & reducing reagents, AlCl3 or FeBr3 Lewis acid catalysts for halogenation via electrophilic aromatic substitution and for Friedel-Crafts alkylation & acylation, etc.

      Edited by UltimaOnline 25 Aug `16, 12:19AM
  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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    • Originally posted by Fxwhy:

      MJC 2015 Prelims Paper 2 

      1e) For the safety hazard, can I write chemical reagents like ethanal are corrosive when it is in contact with the skin and eyes? 

      3a) Where did the ans get 2/4 from? I am also quite weak at approaching this type of qns where do you start?

      3d) Why doesnt the ans include bond length? How do you know when the ans requires you the write bond length or bond energy? 

      Will I be penalised if I write PCl5 at rtp instead of anhydrous PCl5 at rtp?


      Q1e) Ethanal is toxic and carcinogenic, not corrosive.
      https://en.wikipedia.org/wiki/Acetaldehyde#Toxicity

      Q3a) Instead of blindly memorizing and applying a mathematical formula, use common sense. For a uninegatively charged species : when mass is 37g, deflection is merely -1 degrees. Hence when mass is 1g (ie. much lighter), deflection should concordantly be -37 degrees (ie. larger magnitude deflected). Since mass of He is 4g, hence deflection should be -9.25 degrees (if uninegatively charged). Since He nuclei is dipositively charged, hence deflection should be +18.5 degrees.

      Q3d) Bond length here is only indirectly relevant (since bond length is inversely proportional to bond strength, ceteris paribus). It is bond strength which is directly relevant. Hence, there is no need to (ie. no marks awarded for) mentioning bond length.

      Q4ai) It's ok if you don't specify "anhydrous", as long as you do *NOT* specify aqueous (aq) (which would be marked wrong).

      Same for all reagents which need to be anhydrous, eg. LiAlH4 reducing agent, acyl halides for nucleophilic acyl substitution, Grignard nucleophilic & reducing reagents, AlCl3 or FeBr3 Lewis acid catalysts for halogenation via electrophilic aromatic substitution and for Friedel-Crafts alkylation & acylation, etc.

      Edited by UltimaOnline 25 Aug `16, 12:19AM
  • Moderator
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    • Originally posted by Flying grenade:

      both CH3 and Cl are ortho para directors

       

      now the Cl connected to CH2 and then connected to Benzene. can't figure out overall if CH2Cl is e- donating or withdrawing. 

      dun think Cl will be that powerful as to manage to withdraw e- from benzene through one CH2 unit.

      hence my guess is overall CH2Cl is weakly activating ,and hence act as an ortho para director


      Ask your school teacher or private tutor, move on. Edart sterces.

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    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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    • Originally posted by Flying grenade:

      does zwitterion only occur at isoelectric points only? or zwitterions occur at any pH, just that the amount of zwitterions at isoelectric points is the greatest? 

       


      What do you think? Isn't it obvious?!? (well maybe not to Singapore JC H2 students).

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    • Originally posted by Flying grenade:

      thanks for yr reply

       

      page 392

      Esub of NO2+ to chloromethylbenzene, the NO2 can sub at any position??


      No. You have to decide for yourself (based on understanding) if CH2Cl is ortho-para or meta director, unlike Singapore JC students (based on blind memorization).

      Ask your school teacher or private tutor, move on. Edart sterces.

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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  • Moderator
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    • Originally posted by Flying grenade:

      page 377

      will the Ring in Atropine exhibit aromaticity?  it has alternating single and double bonds

      if required to draw in exams, can i draw a circle, representing delocalised pi e- cloud, like benzene? 

      should benzene be included as a functional group, as asked by the qn to name all functional groups present? 

      thanks


      Yes. Yes. Yes.

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    • Originally posted by Flying grenade:

      page 367

      for delocalisation of e- into b.ring, the hybridisation of N atom can be , or is, between sp2 and sp3?

      or is it must be sp2 like C atom?


      image

      Go ask your school teacher or private tutor. Edart sterces.

  • Moderator
    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
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