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2018 H2 Chemistry JC students post your questions here

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    H2 Chemistry @ BedokFunland JC (near VJC & TJC)
    UltimaOnline's Avatar
    14,494 posts since May '05
    • Originally posted by UltimaOnline:

      The following MCQ is a Cambridge A level MCQ, used in both the UK and Singapore papers.

      When iron reacts with aqueous iron(III) ions, iron(II) ions are formed as the only product. A final mixture, after the reaction has taken place, contains equal numbers of moles of Fe2+(aq) and Fe3+(aq). Assuming the reaction has gone to completion, how many moles of Fe(s) and Fe3+(aq) were in the starting mixture?

      I remember coming across a Singapore JC Prelim / Tutorial MCQ which used this MCQ and gave it a twist to make it tougher. I searched for it but can't find it. If anyone recognizes the Singapore JC Prelim / Tutorial MCQ I'm referring to, please post the JC and year, or the MCQ itself, thanks.


      The modified Prelim / Tutorial MCQ could be that the final amount of Fe2+(aq) and Fe3+(aq) were in the molar ratio of 2:1 or 1:2 (or any ratio you like), instead of 1:1. But such a slightly modified MCQ would still be considered easy (to be honest).

      I seem to recall the modified Prelim / Tutorial MCQ being a tad more interesting (students would say 'sadistic') than this, but a pity I forget the exact modification. Anyone recognizes the modified Prelim / Tutorial MCQ I'm referring to, please share it here, thanks.

      Edited by UltimaOnline 13 Jan `18, 9:57PM
    • Came across this in a 2017 Singapore JC Prelim Paper, which shall remain unnamed.

      Marker’s comment : There are still some students who drew mechanism like A --> B --> C --> D, the correct way to draw is A --> B, B --> C, C --> D.

      No, that is just totally wrong. Although Cambridge will accept either way for A level purposes, the correct (ie. University) way, and indeed the way preferred by Cambridge markers at A levels, is to draw A --> B --> C --> D.

      To draw A --> B, B --> C, C --> D is a terribly inefficient and childish way, which Cambridge tolerates but discourages, even at A levels.

      Here's an example of how we draw mechanisms at University levels, and thus also the recommended way for competent (not childish) A level students :

      image

      https://en.wikipedia.org/wiki/Benzoin_condensation

    • image

      [Singapore] - A young woman scholar from the Agency for Science, Technology and Research (A*Star) was suspected to have taken her own life at a laboratory early Tuesday (Jan 16 2018) morning. Colleagues of Katarina Chlebikova, working at the Institute of Molecular and Cell Biology (IMCB), said that the 26-year-old Slovakian had been troubled over work and relationship issues before her death. In response to media queries, the police said that they were alerted to the case at 10.44am on Tuesday. Her body was found on the eighth storey of 61 Biopolis Drive, where the institute is located. “A 26-year-old woman was found motionless and was pronounced dead by paramedics at scene. Police are investigating the unnatural death,” they added. TODAY understands that Chlebikova left behind a note suggesting that she killed herself via nitrogen poisoning.

      http://www.todayonline.com/singapore/astar-scholar-found-dead-lab

      BedokFunland JC's comments on the chemistry involved :

      Nitrogen gas itself is physiologically inert and non-toxic, unlike carbon monoxide. However, deliberately pumping into a room excess nitrogen gas, displaces all other gases from the room, including oxygen. This results in asphyxiation and death from oxygen deprivation, as would occur with carbon monoxide poisoning.

      That this method can be used, and has been used, to carry out covert assassinations, is known to agents of intelligence agencies such as the CIA, Mossad, MI6, KGB, etc. In the case of the 26-year-old Slovakian young woman in Singapore, she used this method for committing suicide.

      Spiritually and karmically, the state of emotional and psychological distress that drove her to commit suicide, will accompany her into the afterlife, and will pose some difficulty in releasing her consciousness from her post-mortem emotional pain and psychosis, and she may need some time to herself before willing to accept and experience love and forgiveness, for sufficient healing of her psychological trauma to occur, before she can move forward vibrationally, onto the intermissive period proper, where further healing, life review and preparation for her next physical incarnation can occur. She will be supported by her guides & helpers at every step of the way, even if she may not be aware of it through her emotional pain. Rest in peace now, Miss Katarina Chlebikova.

      image

      Photo : https://sg.news.yahoo.com/duke-nus-medical-school-student-found-dead-biopolis-laboratory-051706805.html

      Edited by UltimaOnline 17 Jan `18, 4:09PM
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