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Hi, I have a question regarding NJC 2013 Prelim P1 Q14.
How to derive half life? Since it's a first order reaction, I know k = (ln2)/half-life.
I know that 10 mins into reaction, Pa + Pb = 600Pa,
And at the end of reaction, Pa + Pb = 400Pa.
What should I do with the data given?
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Originally posted by supercat:
Hi, I have a question regarding NJC 2013 Prelim P1 Q14.
How to derive half life? Since it's a first order reaction, I know k = (ln2)/half-life.
I know that 10 mins into reaction, Pa + Pb = 600Pa,
And at the end of reaction, Pa + Pb = 400Pa.
What should I do with the data given?
At end of reaction, partial pressure of B is 400 Pa. Hence initial partial pressure of A is 800 Pa. Hence, 1 half-life into the reaction, partial pressure of A is 400 Pa, and B is 200 Pa. That's a total pressure of 600 Pa. Hence, each half-life must be 10 min. Since half-life = ln 2 / k, hence k = ln 2 / half-life, which is calculated out to be 0.0693 min-1.For A level purposes, such questions will be kept mathematically simple (such as in this case), to avoid necessitating the use of calculus and integrated rate laws.
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for 2015 chem olympiad qn 3 on Ritalin,
for the structure of compounds,
for cpd F to ritalin, why isn't benzene ring reduced? and the imine reduce to secondary amine?
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Originally posted by Flying grenade:
for 2015 chem olympiad qn 3 on Ritalin,
for the structure of compounds,
for cpd F to ritalin, why isn't benzene ring reduced? and the imine reduce to secondary amine?
Aromaticity resists hydrogenation. For A level purposes, unless hinted by the question with extraordinarily high temperatures and pressures, you are to take it that the benzene ring does not get hydrogenated under normal reaction conditions required to hydrogenate or reduce other organic functional groups. -
Originally posted by UltimaOnline:
Aromaticity resists hydrogenation. For A level purposes, unless hinted by the question with extraordinarily high temperatures and pressures, you are to take it that the benzene ring does not get hydrogenated under normal reaction conditions required to hydrogenate or reduce other organic functional groups.from Internet, benzene ring gets hydrogenated to form cyclohexane, under similar conditions
but you're the most trustworthy source.
Thanks for alleviating our stress with your kind and trustworthy replies in this uncertain world, UltimaOnline !
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Originally posted by Flying grenade:
from Internet, benzene ring gets hydrogenated to form cyclohexane, under similar conditions
but you're the most trustworthy source.
Okay, thank you Ultima for your kind replies !
Read your CS Toh Adv Study Guide, compare the exact temperature and pressure required to hydrogenate benzene vs alkene vs alkyne vs ketone vs aldehyde vs nitrile vs amide etc. Don't need to post here, just read silently for yourself. -
what's the geometry of methyl radical?
trigonal pyramidal or quasi-trigonal planar?
for A levels, we draw trigonal pyramidal and write bond angle more than 109.5° or between 109.5 and 107.5° ?
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Originally posted by Flying grenade:
what's the geometry of methyl radical?
trigonal pyramidal or quasi-trigonal planar?
for A levels, we draw trigonal pyramidal and write bond angle more than 109.5° or between 109.5 and 107.5° ?
If CF3 radical, then trigonal pyramidal. If CH3 radical, then trigonal planar. Reasons for the difference are beyond the H2 syllabus (a hint for A grade students : ask yourself what possible thermodynamic advantage could a CH3 radical gain by adopting sp2 hybridization, versus what possible thermodynamic advantage could a CF3 radical gain by adopting sp3 hybridization, taking into consideration the contrasting natures of s and p orbitals), go ask your school teacher or private tutor if you're interested.Cambridge is reasonable. As long as you give chemically reasonable justifications for your answer, Cambridge (in most cases) will accept a variety of reasonable answers (eg. a range for bond angles, explanation & justification for either geometry for either radical), especially for beyond-syllabus questions such as these.
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larger electron cloud size , more polarisable electron cloud, easier to sublime/decompose, or more difficult??
e.g. AlCl3 to AlI3. i know from AlCl3 to AlI3 , larger electron cloud so have more extensive idid forces of attraction, and hence higher B.P.
for the weakening of intramolecular bond, does more polarisable e- cloud means easier to weaken the intramolecular bond(e.g. NO3- or CO32-) , or is it like easier to polarise/more polarisable hence stronger covalent bond formed between metal cation and the anion?
if larger and more polarisable/easier to polarise e- cloud hence easier to decompose, then why AlCl3 have higher propensity to sublime compared to AlI3 (or is it) ?
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yes aluminium halides are interesting, just only a little bit confusing, with their solid state, dimerisation, gaseous state, sublimation
https://en.m.wikipedia.org/wiki/Aluminium_chloride
https://en.m.wikipedia.org/wiki/Aluminium_bromide
https://en.m.wikipedia.org/wiki/Aluminium_iodide
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Alevel 2015 p1 qn 39
i know phenol in thymol can react with the OH- in alkaline KMnO4 , but can alkaline KMnO4 oxidise the benzylic carbon that contains the benzylic Hydrogen in Thymol?
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Originally posted by Flying grenade:
larger electron cloud size , more polarisable electron cloud, easier to sublime/decompose, or more difficult??
e.g. AlCl3 to AlI3. i know from AlCl3 to AlI3 , larger electron cloud so have more extensive idid forces of attraction, and hence higher B.P.
for the weakening of intramolecular bond, does more polarisable e- cloud means easier to weaken the intramolecular bond(e.g. NO3- or CO32-) , or is it like easier to polarise/more polarisable hence stronger covalent bond formed between metal cation and the anion?
if larger and more polarisable/easier to polarise e- cloud hence easier to decompose, then why AlCl3 have higher propensity to sublime compared to AlI3 (or is it) ?
No. It looks like you've quite a number (I count at least 3) misconceptions here. Go ask your school teacher or private tutor to go through point by point. -
Originally posted by Flying grenade:
Alevel 2015 p1 qn 39
i know phenol in thymol can react with the OH- in alkaline KMnO4 , but can alkaline KMnO4 oxidise the benzylic carbon that contains the benzylic Hydrogen in Thymol?
If heated under reflux, yes. -
N11/p1/26
is it possible for 1,2-butandiol to exist(and with only one chiral centre )
oxidised to 1-hydroxybut-2-one or 2-hydroxybutan-1-al
oxidised to butan-1,2-dione ? or is it too unstable
sorry my blunder.
butan-1,2-dione doesn't exist.
only 2-oxobutan-1-al (aldehyde and ketone in the same molecule)
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vicinal diol and vicinal diketone
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N09/1/25
is it because its warm, and not hot conditions, thus the C=C double bond in cortisone is not cleaved?
figured out : from other Cambridge's qns, Hot will result in oxidative cleavage of C=C bond, warm will not
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N07/1/24
why option B cannot? carboxylate salt not basic enough, cannot abstract H+ from water? -
Originally posted by Flying grenade:
N11/p1/26
is it possible for 1,2-butandiol to exist(and with only one chiral centre )
oxidised to 1-hydroxybut-2-one or 2-hydroxybutan-1-al
oxidised to butan-1,2-dione ? or is it too unstable
Yes, everything you mentioned is possible. But exactly which intermediate is favored as the major intermediate, depends on the identity (hence mechanism) of the specific oxidizing agent and conditions (eg. temperature, solvent, etc) used. -
Hi UltimaOnliine, for Raymond Chang question on Buffers, is my workings correct? Thanks!
https://www.instagram.com/p/BKBbf4eBl7Y/?taken-by=lolwerwdr
my answer is 1.83 moldm^-3
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Originally posted by Flying grenade:
N07/1/24
why option B cannot? carboxylate salt not basic enough, cannot abstract H+ from water?
Most carboxylate salts are basic enough, but here the 3 Cl atoms are collectively strongly electron-withdrawing by induction, resulting in the CCl3COO- ion being too weak a base to undergo significant hydrolysis. -
Cstoh A level solutions for N09/P3/qn 3a , writes P4 burns in O2 with a pale bluish green flame, not right, should be white flame, backed up by chemguide and Wikipedia
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Originally posted by MightyBiscuits:
Hi UltimaOnliine, for Raymond Chang question on Buffers, is my workings correct? Thanks!
https://www.instagram.com/p/BKBbf4eBl7Y/?taken-by=lolwerwdr
my answer is 1.83 moldm^-3
Incorrect. You need to consider Ksp and Kb separately, and work with both to arrive at the correct answer. -
Originally posted by Flying grenade:
Cstoh A level solutions for N09/P3/qn 3a , writes P4 burns in O2 with a pale bluish green flame, not right, should be white flame, backed up by chemguide and Wikipedia
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N13/1/20
can resonance occur in the straight chain of the molecule(and therefore throughout the whole molecule including the benzene ring) ? the region indicated by "z" in the qn
if yes, then that molecule shown in the qn, is one of the many resonance contributors?